Amiga Plus 1995 #2/Amiga Plus CD - 1995 - No. 2.iso/internet/faq/englisch/unix

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Archive-name: unix-faq/faq/contents
Version: $Id: contents,v 2.5 1994/04/28 19:25:03 tmatimar Exp tmatimar $

The following seven articles contain the answers to some Frequently Asked
Questions often seen in comp.unix.questions and comp.unix.shell.
Please don't ask these questions again, they've been answered plenty
of times already - and please don't flame someone just because they may
not have read this particular posting.  Thank you.

This collection of documents is Copyright (c) 1994, Ted Timar, except
Part 6, which is Copyright (c) 1994, Pierre Lewis and Ted Timar.
All rights reserved.  Permission to distribute the collection is
hereby granted providing that distribution is electronic, no money
is involved, reasonable attempts are made to use the latest version
and all credits and this copyright notice are maintained.
Other requests for distribution will be considered.  All reasonable
requests will be granted.

All information here has been contributed with good intentions, but
none of it is guaranteed either by the contributors or myself to be
accurate.  The users of this information take all responsibility for
any damage that may occur.

Many FAQs, including this one, are available on the archive site
rtfm.mit.edu in the directory pub/usenet/news.answers.
The name under which a FAQ is archived appears in the "Archive-Name:"
line at the top of the article.  This FAQ is archived as
"unix-faq/faq/part[1-7]".

These articles are divided approximately as follows:

      1.*) General questions.
      2.*) Relatively basic questions, likely to be asked by beginners.
      3.*) Intermediate questions.
      4.*) Advanced questions, likely to be asked by people who thought
           they already knew all of the answers.
      5.*) Questions pertaining to the various shells, and the differences.
      6.*) An overview of Unix variants.
      7.*) An comparison of configuration management systems (RCS, SCCS).

The following questions are answered:

      1.1)  Who helped you put this list together?
      1.2)  When someone refers to 'rn(1)' or 'ctime(3)', what does
              the number in parentheses mean?
      1.3)  What does {some strange unix command name} stand for?
      1.4)  How does the gateway between "comp.unix.questions" and the
              "info-unix" mailing list work?
      1.5)  What are some useful Unix or C books?
      1.6)  What happened to the pronunciation list that used to be
              part of this document?

      2.1)  How do I remove a file whose name begins with a "-" ?
      2.2)  How do I remove a file with funny characters in the filename ?
      2.3)  How do I get a recursive directory listing?
      2.4)  How do I get the current directory into my prompt?
      2.5)  How do I read characters from the terminal in a shell script?
      2.6)  How do I rename "*.foo" to "*.bar", or change file names
              to lowercase?
      2.7)  Why do I get [some strange error message] when I
              "rsh host command" ?
      2.8)  How do I {set an environment variable, change directory} inside a
              program or shell script and have that change affect my
              current shell?
      2.9)  How do I redirect stdout and stderr separately in csh?
      2.10) How do I tell inside .cshrc if I'm a login shell?
      2.11) How do I construct a shell glob-pattern that matches all files
            except "." and ".." ?
      2.12) How do I find the last argument in a Bourne shell script?
      2.13) What's wrong with having '.' in your $PATH ?
      2.14) How do I ring the terminal bell during a shell script?
      2.15) Why can't I use "talk" to talk with my friend on machine X?
      2.16) Why does calendar produce the wrong output?

      3.1)  How do I find the creation time of a file?
      3.2)  How do I use "rsh" without having the rsh hang around
              until the remote command has completed?
      3.3)  How do I truncate a file?
      3.4)  Why doesn't find's "{}" symbol do what I want?
      3.5)  How do I set the permissions on a symbolic link?
      3.6)  How do I "undelete" a file?
      3.7)  How can a process detect if it's running in the background?
      3.8)  Why doesn't redirecting a loop work as intended?  (Bourne shell)
      3.9)  How do I run 'passwd', 'ftp', 'telnet', 'tip' and other interactive
              programs from a shell script or in the background?
      3.10) How do I find the process ID of a program with a particular
            name from inside a shell script or C program?
      3.11) How do I check the exit status of a remote command
            executed via "rsh" ?
      3.12) Is it possible to pass shell variable settings into an awk program?
      3.13) How do I get rid of zombie processes that persevere?
      3.14) How do I get lines from a pipe as they are written instead of
            only in larger blocks.

      4.1)  How do I read characters from a terminal without requiring the user
              to hit RETURN?
      4.2)  How do I check to see if there are characters to be read without
              actually reading?
      4.3)  How do I find the name of an open file?
      4.4)  How can an executing program determine its own pathname?
      4.5)  How do I use popen() to open a process for reading AND writing?
      4.6)  How do I sleep() in a C program for less than one second?
      4.7)  How can I get setuid shell scripts to work?
      4.8)  How can I find out which user or process has a file open or is using
            a particular file system (so that I can unmount it?)
      4.9)  How do I keep track of people who are fingering me?
      4.10) Is it possible to reconnect a process to a terminal after it has
            been disconnected, e.g. after starting a program in the background
            and logging out?
      4.11) Is it possible to "spy" on a terminal, displaying the output
            that's appearing on it on another terminal?

      5.1)  Can shells be classified into categories?
      5.2)  How do I "include" one shell script from within another
            shell script?
      5.3)  Do all shells have aliases?  Is there something else that
            can be used?
      5.4)  How are shell variables assigned?
      5.5)  How can I tell if I am running an interactive shell?
      5.6)  What "dot" files do the various shells use?
      5.7)  I would like to know more about the differences between the
            various shells.  Is this information available some place?

      6.1)  Disclaimer and introduction.
      6.2)  A very brief look at Unix history.
      6.3)  Main Unix flavors.
      6.4)  Unix Standards.
      6.5)  Identifying your Unix flavor.
      6.6)  Brief notes on some well-known (commercial/PD) Unices.
      6.7)  Real-time Unices.
      6.8)  Unix glossary.
      6.9)  Acknowledgements.

      7.1)  RCS vs SCCS:  Introduction
      7.2)  RCS vs SCCS:  How do the interfaces compare?
      7.3)  RCS vs SCCS:  What's in a Revision File?
      7.4)  RCS vs SCCS:  What are the keywords?
      7.5)  What's an RCS symbolic name?
      7.6)  RCS vs SCCS:  How do they compare for performance?
      7.7)  RCS vs SCCS:  Version Identification.
      7.8)  RCS vs SCCS:  How do they handle with problems?
      7.9)  RCS vs SCCS:  How do they interact with make(1)?
      7.10) RCS vs SCCS:  Conversion.
      7.11) RCS vs SCCS:  Support
      7.12) RCS vs SCCS:  Command Comparison
      7.13) RCS vs SCCS:  Acknowledgements
      7.14) Can I get more information on configuration management systems?

      If you're looking for the answer to, say, question 2.5, look in
      part 2 and search for the regular expression "^2.5)".

While these are all legitimate questions, they seem to crop up in
comp.unix.questions or comp.unix.shell on an annual basis, usually
followed by plenty of replies (only some of which are correct) and then
a period of griping about how the same questions keep coming up.  You
may also like to read the monthly article "Answers to Frequently Asked
Questions" in the newsgroup "news.announce.newusers", which will tell
you what "UNIX" stands for.

With the variety of Unix systems in the world, it's hard to guarantee
that these answers will work everywhere.  Read your local manual pages
before trying anything suggested here.  If you have suggestions or
corrections for any of these answers, please send them to to
[e-mail].

--
Ted Timar - [e-mail]
ISG Technologies Inc., 6509 Airport Road, Mississauga, Ontario, Canada L4V 1S7
Archive-name: unix-faq/faq/part1
Version: $Id: part1,v 2.5 1994/04/28 19:25:03 tmatimar Exp tmatimar $

These seven articles contain the answers to some Frequently Asked
Questions often seen in comp.unix.questions and comp.unix.shell.
Please don't ask these questions again, they've been answered plenty
of times already - and please don't flame someone just because they may
not have read this particular posting.  Thank you.

This collection of documents is Copyright (c) 1994, Ted Timar, except
Part 6, which is Copyright (c) 1994, Pierre Lewis and Ted Timar.
All rights reserved.  Permission to distribute the collection is
hereby granted providing that distribution is electronic, no money
is involved, reasonable attempts are made to use the latest version
and all credits and this copyright notice are maintained.
Other requests for distribution will be considered.  All reasonable
requests will be granted.

All information here has been contributed with good intentions, but
none of it is guaranteed either by the contributors or myself to be
accurate.  The users of this information take all responsibility for
any damage that may occur.

Many FAQs, including this one, are available on the archive site
rtfm.mit.edu in the directory pub/usenet/news.answers.
The name under which a FAQ is archived appears in the "Archive-Name:"
line at the top of the article.  This FAQ is archived as
"unix-faq/faq/part[1-7]".

These articles are divided approximately as follows:

      1.*) General questions.
      2.*) Relatively basic questions, likely to be asked by beginners.
      3.*) Intermediate questions.
      4.*) Advanced questions, likely to be asked by people who thought
           they already knew all of the answers.
      5.*) Questions pertaining to the various shells, and the differences.
      6.*) An overview of Unix variants.
      7.*) An comparison of configuration management systems (RCS, SCCS).

This article includes answers to:

      1.1)  Who helped you put this list together?
      1.2)  When someone refers to 'rn(1)' or 'ctime(3)', what does
              the number in parentheses mean?
      1.3)  What does {some strange unix command name} stand for?
      1.4)  How does the gateway between "comp.unix.questions" and the
              "info-unix" mailing list work?
      1.5)  What are some useful Unix or C books?
      1.6)  What happened to the pronunciation list that used to be
              part of this document?

If you're looking for the answer to, say, question 1.5, and want to skip
everything else, you can search ahead for the regular expression "^1.5)".

While these are all legitimate questions, they seem to crop up in
comp.unix.questions or comp.unix.shell on an annual basis, usually
followed by plenty of replies (only some of which are correct) and then
a period of griping about how the same questions keep coming up.  You
may also like to read the monthly article "Answers to Frequently Asked
Questions" in the newsgroup "news.announce.newusers", which will tell
you what "UNIX" stands for.

With the variety of Unix systems in the world, it's hard to guarantee
that these answers will work everywhere.  Read your local manual pages
before trying anything suggested here.  If you have suggestions or
corrections for any of these answers, please send them to to
[e-mail].

----------------------------------------------------------------------

Subject: Who helped you put this list together?
Date: Thu Mar 18 17:16:55 EST 1993

1.1)  Who helped you put this list together?

      Happy Birthday Unix FAQ.  The Unix FAQ is now over 5 years old!
      Everyone who ever contributed to this FAQ is encouraged to go out
      and have a piece of birthday cake.  Unfortunately, I can't distribute
      the cake by email, so you'll have to make your own.  :-)

      This document was one of the first collections of Frequently Asked
      Questions.  It was originally compiled in July 1989.

      I took over the maintenance of this list.  Almost all of the work
      (and the credit) for generating this compilation was done by
      Steve Hayman.

      We also owe a great deal of thanks to dozens of Usenet readers who
      submitted questions, answers, corrections and suggestions for this
      list.  Special thanks go to Maarten Litmaath, Guy Harris and
      Jonathan Kamens, who have all made many especially valuable
      contributions.

      Part 5 of this document (shells) was written almost entirely by
      Matthew Wicks <[e-mail]>.

      Part 6 of this document (Unix flavours) was written almost entirely by
      Pierre (P.) Lewis <[e-mail]>.

      Where possible the author of each question and the date it was last
      updated is given at the top.  Unfortunately, I only started this
      practice recently, and much of the information is lost.  I was also
      negligent in keeping track of who provided updates to questions.
      Sorry to those who have made valuable contributions, but did not
      receive the credit and recognition that they legitimately deserve.

      I make this document available in *roff format (ms and mm macro
      packages).  Andrew Cromarty has also converted it into Texinfo format.

------------------------------

Subject: When someone refers to 'rn(1)' ...  the number in parentheses mean?
Date: Thu Mar 18 17:16:55 EST 1993

1.2)  When someone refers to 'rn(1)' or 'ctime(3)', what does
      the number in parentheses mean?

      It looks like some sort of function call, but it isn't.  These
      numbers refer to the section of the "Unix manual" where the
      appropriate documentation can be found.  You could type
      "man 3 ctime" to look up the manual page for "ctime" in section 3
      of the manual.

      The traditional manual sections are:

        1       User-level  commands
        2       System calls
        3       Library functions
        4       Devices and device drivers
        5       File formats
        6       Games
        7       Various miscellaneous stuff - macro packages etc.
        8       System maintenance and operation commands

      Some Unix versions use non-numeric section names.  For instance,
      Xenix uses "C" for commands and "S" for functions.  Some newer
      versions of Unix require "man -s# title" instead of "man # title".

      Each section has an introduction, which you can read with "man #
      intro" where # is the section number.

      Sometimes the number is necessary to differentiate between a
      command and a library routine or system call of the same name.
      For instance, your system may have "time(1)", a manual page about
      the 'time' command for timing programs, and also "time(3)", a
      manual page about the 'time' subroutine for determining the
      current time.  You can use "man 1 time" or "man 3 time" to
      specify which "time" man page you're interested in.

      You'll often find other sections for local programs or even
      subsections of the sections above - Ultrix has sections 3m, 3n,
      3x and 3yp among others.

------------------------------

Subject: What does {some strange unix command name} stand for?
Date: Thu Mar 18 17:16:55 EST 1993

1.3)  What does {some strange unix command name} stand for?

      awk = "Aho Weinberger and Kernighan"

        This language was named by its authors, Al Aho, Peter
        Weinberger and Brian Kernighan.

      grep = "Global Regular Expression Print"

        grep comes from the ed command to print all lines matching a
        certain pattern

                    g/re/p

        where "re" is a "regular expression".

      fgrep = "Fixed GREP".

        fgrep searches for fixed strings only.  The "f" does not stand
        for "fast" - in fact, "fgrep foobar *.c" is usually slower than
        "egrep foobar *.c"  (Yes, this is kind of surprising. Try it.)

        Fgrep still has its uses though, and may be useful when searching
        a file for a larger number of strings than egrep can handle.

      egrep = "Extended GREP"

        egrep uses fancier regular expressions than grep.  Many people
        use egrep all the time, since it has some more sophisticated
        internal algorithms than grep or fgrep, and is usually the
        fastest of the three programs.

      cat = "CATenate"

        catenate is an obscure word meaning "to connect in a series",
        which is what the "cat" command does to one or more files.  Not
        to be confused with C/A/T, the Computer Aided Typesetter.

      gecos = "General Electric Comprehensive Operating System"

        When GE's large systems division was sold to Honeywell,
        Honeywell dropped the "E" from "GECOS".

        Unix's password file has a "pw_gecos" field.  The name is a
        real holdover from the early days.  Dennis Ritchie has reported:

            "Sometimes we sent printer output or batch jobs
             to the GCOS machine.  The gcos field in the password file
             was a place to stash the information for the $IDENT card.
             Not elegant."

      nroff = "New ROFF"
      troff = "Typesetter new ROFF"

        These are descendants of "roff", which was a re-implementation
        of the Multics "runoff" program (a program that you'd use to
        "run off" a good copy of a document).

      tee       = T

        From plumbing terminology for a T-shaped pipe splitter.

      bss = "Block Started by Symbol"

        Dennis Ritchie says:

            Actually the acronym (in the sense we took it up; it may
            have other credible etymologies) is "Block Started by
            Symbol." It was a pseudo-op in FAP (Fortran Assembly [-er?]
            Program), an assembler for the IBM 704-709-7090-7094
            machines.  It defined its label and set aside space for a
            given number of words.  There was another pseudo-op, BES,
            "Block Ended by Symbol" that did the same except that the
            label was defined by the last assigned word + 1.  (On these
            machines Fortran arrays were stored backwards in storage
            and were 1-origin.)

            The usage is reasonably appropriate, because just as with
            standard Unix loaders, the space assigned didn't have to be
            punched literally into the object deck but was represented
            by a count somewhere.

      biff = "BIFF"

        This command, which turns on asynchronous mail notification,
        was actually named after a dog at Berkeley.

            I can confirm the origin of biff, if you're interested.
            Biff was Heidi Stettner's dog, back when Heidi (and I, and
            Bill Joy) were all grad students at U.C. Berkeley and the
            early versions of BSD were being developed.   Biff was
            popular among the residents of Evans Hall, and was known
            for barking at the mailman, hence the name of the command.

        Confirmation courtesy of Eric Cooper, Carnegie Mellon University

      rc (as in ".cshrc" or "/etc/rc") = "RunCom"

        "rc" derives from "runcom", from the MIT CTSS system, ca. 1965.

            'There was a facility that would execute a bunch of
            commands stored in a file; it was called "runcom" for "run
            commands", and the file began to be called "a runcom."

            "rc" in Unix is a fossil from that usage.'

        Brian Kernighan & Dennis Ritchie, as told to Vicki Brown

        "rc" is also the name of the shell from the new Plan 9
        operating system.

      Perl = "Practical Extraction and Report Language"
      Perl = "Pathologically Eclectic Rubbish Lister"

        The Perl language is Larry Wall's highly popular
        freely-available completely portable text, process, and file
        manipulation tool that bridges the gap between shell and C
        programming (or between doing it on the command line and
        pulling your hair out).  For further information, see the
        Usenet newsgroup comp.lang.perl.

      Don Libes' book "Life with Unix" contains lots more of these
      tidbits.

------------------------------

Subject: How does the gateway between "comp.unix.questions" ... work ?
Date: Thu Mar 18 17:16:55 EST 1993

1.4)  How does the gateway between "comp.unix.questions" and the
      "info-unix" mailing list work?

      "info-unix" and "unix-wizards" are mailing list versions of
      comp.unix.questions and comp.unix.wizards respectively.
      There should be no difference in content between the
      mailing list and the newsgroup.

      To get on or off either of these lists, send mail to
      [e-mail] or [e-mail].
      Be sure to use the '-Request'.  Don't expect an immediate response.

      Here are the gory details, courtesy of the list's maintainer,
      Bob Reschly.

      ==== postings to info-UNIX and UNIX-wizards lists ====

      Anything submitted to the list is posted; I do not moderate
      incoming traffic -- BRL functions as a reflector.  Postings
      submitted by Internet subscribers should be addressed to the list
      address (info-UNIX or UNIX- wizards);  the '-request' addresses
      are for correspondence with the list maintainer [me].  Postings
      submitted by USENET readers should be addressed to the
      appropriate news group (comp.unix.questions or
      comp.unix.wizards).

      For Internet subscribers, received traffic will be of two types;
      individual messages, and digests.  Traffic which comes to BRL
      from the Internet and BITNET (via the BITNET-Internet gateway) is
      immediately resent to all addressees on the mailing list.
      Traffic originating on USENET is gathered up into digests which
      are sent to all list members daily.

      BITNET traffic is much like Internet traffic.  The main
      difference is that I maintain only one address for traffic
      destined to all BITNET subscribers. That address points to a list
      exploder which then sends copies to individual BITNET
      subscribers.  This way only one copy of a given message has to
      cross the BITNET-Internet gateway in either direction.

      USENET subscribers see only individual messages.  All messages
      originating on the Internet side are forwarded to our USENET
      machine.  They are then posted to the appropriate newsgroup.
      Unfortunately, for gatewayed messages, the sender becomes
      "news@brl-adm".  This is currently an unavoidable side-effect of
      the software which performs the gateway function.

      As for readership, USENET has an extremely large readership - I
      would guess several thousand hosts and tens of thousands of
      readers.  The master list maintained here at BRL runs about two
      hundred fifty entries with roughly ten percent of those being
      local redistribution lists.  I don't have a good feel for the
      size of the BITNET redistribution, but I would guess it is
      roughly the same size and composition as the master list.
      Traffic runs 150K to 400K bytes per list per week on average.

------------------------------

Subject: What are some useful Unix or C books?
Date: Thu Mar 18 17:16:55 EST 1993

1.5)  What are some useful Unix or C books?

      Mitch Wright ([e-mail]) maintains a useful list of Unix
      and C books, with descriptions and some mini-reviews.  There are
      currently 167 titles on his list.

      You can obtain a copy of this list by anonymous ftp from
      ftp.rahul.net (192.160.13.1), where it's "pub/mitch/YABL/yabl".
      Send additions or suggestions to [e-mail].

      Samuel Ko ([e-mail]) maintains another list of Unix books.
      This list contains only recommended books, and is therefore
      somewhat shorter.  This list is also a classified list, with
      books grouped into categories, which may be better if you are
      looking for a specific type of book.

      You can obtain a copy of this list by anonymous ftp from
      rtfm.mit.edu, where it's "pub/usenet/news.answers/books/unix".
      Send additions or suggestions to [e-mail].

      If you can't use anonymous ftp, email the line "help" to
      "[e-mail]" for instructions on retrieving
      things via email.

------------------------------

Subject: What happened to the pronunciation list ... ?
Date: Thu Mar 18 17:16:55 EST 1993

1.6)  What happened to the pronunciation list that used to be part of this
      document?

      From its inception in 1989, this FAQ document included a
      comprehensive pronunciation list maintained by Maarten Litmaath
      (thanks, Maarten!).  It was originally created by Carl Paukstis
      <[e-mail]>.

      It has been retired, since it is not really relevant to the topic
      of "Unix questions".  You can still find it as part of the
      widely-distributed "Jargon" file (maintained by Eric S. Raymond,
      [e-mail]) which seems like a much more appropriate
      forum for the topic of "How do you pronounce  /* ?"

      If you'd like a copy, you can ftp one from ftp.wg.omron.co.jp
      (133.210.4.4), it's "pub/unix-faq/docs/Pronunciation-Guide".

------------------------------

End of unix/faq Digest part 1 of 7
**********************************

--
Ted Timar - [e-mail]
ISG Technologies Inc., 6509 Airport Road, Mississauga, Ontario, Canada L4V 1S7
Archive-name: unix-faq/faq/part2
Version: $Id: part2,v 2.5 1994/04/28 19:25:03 tmatimar Exp tmatimar $

These seven articles contain the answers to some Frequently Asked
Questions often seen in comp.unix.questions and comp.unix.shell.
Please don't ask these questions again, they've been answered plenty
of times already - and please don't flame someone just because they may
not have read this particular posting.  Thank you.

This collection of documents is Copyright (c) 1994, Ted Timar, except
Part 6, which is Copyright (c) 1994, Pierre Lewis and Ted Timar.
All rights reserved.  Permission to distribute the collection is
hereby granted providing that distribution is electronic, no money
is involved, reasonable attempts are made to use the latest version
and all credits and this copyright notice are maintained.
Other requests for distribution will be considered.  All reasonable
requests will be granted.

All information here has been contributed with good intentions, but
none of it is guaranteed either by the contributors or myself to be
accurate.  The users of this information take all responsibility for
any damage that may occur.

Many FAQs, including this one, are available on the archive site
rtfm.mit.edu in the directory pub/usenet/news.answers.
The name under which a FAQ is archived appears in the "Archive-Name:"
line at the top of the article.  This FAQ is archived as
"unix-faq/faq/part[1-7]".

These articles are divided approximately as follows:

      1.*) General questions.
      2.*) Relatively basic questions, likely to be asked by beginners.
      3.*) Intermediate questions.
      4.*) Advanced questions, likely to be asked by people who thought
             they already knew all of the answers.
      5.*) Questions pertaining to the various shells, and the differences.
      6.*) An overview of Unix variants.
      7.*) An comparison of configuration management systems (RCS, SCCS).

This article includes answers to:

      2.1)  How do I remove a file whose name begins with a "-" ?
      2.2)  How do I remove a file with funny characters in the filename ?
      2.3)  How do I get a recursive directory listing?
      2.4)  How do I get the current directory into my prompt?
      2.5)  How do I read characters from the terminal in a shell script?
      2.6)  How do I rename "*.foo" to "*.bar", or change file names
              to lowercase?
      2.7)  Why do I get [some strange error message] when I
              "rsh host command" ?
      2.8)  How do I {set an environment variable, change directory} inside a
              program or shell script and have that change affect my
              current shell?
      2.9)  How do I redirect stdout and stderr separately in csh?
      2.10) How do I tell inside .cshrc if I'm a login shell?
      2.11) How do I construct a shell glob-pattern that matches all files
            except "." and ".." ?
      2.12) How do I find the last argument in a Bourne shell script?
      2.13) What's wrong with having '.' in your $PATH ?
      2.14) How do I ring the terminal bell during a shell script?
      2.15) Why can't I use "talk" to talk with my friend on machine X?
      2.16) Why does calendar produce the wrong output?

If you're looking for the answer to, say, question 2.5, and want to skip
everything else, you can search ahead for the regular expression "^2.5)".

While these are all legitimate questions, they seem to crop up in
comp.unix.questions or comp.unix.shell on an annual basis, usually
followed by plenty of replies (only some of which are correct) and then
a period of griping about how the same questions keep coming up.  You
may also like to read the monthly article "Answers to Frequently Asked
Questions" in the newsgroup "news.announce.newusers", which will tell
you what "UNIX" stands for.

With the variety of Unix systems in the world, it's hard to guarantee
that these answers will work everywhere.  Read your local manual pages
before trying anything suggested here.  If you have suggestions or
corrections for any of these answers, please send them to to
[e-mail].

----------------------------------------------------------------------

Subject: How do I remove a file whose name begins with a "-" ?
Date: Thu Mar 18 17:16:55 EST 1993

2.1)  How do I remove a file whose name begins with a "-" ?

      Figure out some way to name the file so that it doesn't begin
      with a dash.  The simplest answer is to use

            rm ./-filename

      (assuming "-filename" is in the current directory, of course.)
      This method of avoiding the interpretation of the "-" works with
      other commands too.

      Many commands, particularly those that have been written to use
      the "getopt(3)" argument parsing routine, accept a "--" argument
      which means "this is the last option, anything after this is not
      an option", so your version of rm might handle "rm -- -filename".
      Some versions of rm that don't use getopt() treat a single "-"
      in the same way, so you can also try "rm - -filename".

------------------------------

Subject: How do I remove a file with funny characters in the filename ?
Date: Thu Mar 18 17:16:55 EST 1993

2.2)  How do I remove a file with funny characters in the filename ?

      If the 'funny character' is a '/', skip to the last part of this
      answer.  If the funny character is something else, such as a ' '
      or control character or character with the 8th bit set, keep reading.

      The classic answers are

        rm -i some*pattern*that*matches*only*the*file*you*want

        which asks you whether you want to remove each file matching
        the indicated pattern;  depending on your shell, this may not
        work if the filename has a character with the 8th bit set (the
        shell may strip that off);

      and

        rm -ri .

        which asks you whether to remove each file in the directory.
        Answer "y" to the problem file and "n" to everything else.
        Unfortunately this doesn't work with many versions of rm.  Also
        unfortunately, this will walk through every subdirectory of ".",
        so you might want to "chmod a-x" those directories temporarily
        to make them unsearchable.

        Always take a deep breath and think about what you're doing and
        double check what you typed when you use rm's "-r" flag or a
        wildcard on the command line;

      and

        find . -type f ... -ok rm '{}' \;

      where "..." is a group of predicates that uniquely identify the
      file.  One possibility is to figure out the inode number of the
      problem file (use "ls -i .") and then use

        find . -inum 12345 -ok rm '{}' \;

      or
        find . -inum 12345 -ok mv '{}' new-file-name \;

      "-ok" is a safety check - it will prompt you for confirmation of
      the command it's about to execute.  You can use "-exec" instead
      to avoid the prompting, if you want to live dangerously, or if
      you suspect that the filename may contain a funny character
      sequence that will mess up your screen when printed.

      What if the filename has a '/' in it?

      These files really are special cases, and can only be created by
      buggy kernel code (typically by implementations of NFS that don't
      filter out illegal characters in file names from remote
      machines.)  The first thing to do is to try to understand exactly
      why this problem is so strange.

      Recall that Unix directories are simply pairs of filenames and
      inode numbers.  A directory essentially contains information
      like this:

        filename  inode

        file1     12345
        file2.c   12349
        file3     12347

      Theoretically, '/' and '\0' are the only two characters that
      cannot appear in a filename - '/' because it's used to separate
      directories and files, and '\0' because it terminates a filename.

      Unfortunately some implementations of NFS will blithely create
      filenames with embedded slashes in response to requests from
      remote machines.  For instance, this could happen when someone on
      a Mac or other non-Unix machine decides to create a remote NFS
      file on your Unix machine with the date in the filename.  Your
      Unix directory then has this in it:

        filename  inode

        91/02/07  12357

      No amount of messing around with 'find' or 'rm' as described
      above will delete this file, since those utilities and all other
      Unix programs, are forced to interpret the '/' in the normal way.

      Any ordinary program will eventually try to do
      unlink("91/02/07"), which as far as the kernel is concerned means
      "unlink the file 07 in the subdirectory 02 of directory 91", but
      that's not what we have - we have a *FILE* named "91/02/07" in
      the current directory.  This is a subtle but crucial distinction.

      What can you do in this case?  The first thing to try is to
      return to the Mac that created this crummy entry, and see if you
      can convince it and your local NFS daemon to rename the file to
      something without slashes.

      If that doesn't work or isn't possible, you'll need help from
      your system manager, who will have to try the one of the
      following.  Use "ls -i" to find the inode number of this bogus
      file, then unmount the file system and use "clri" to clear the
      inode, and "fsck" the file system with your fingers crossed.
      This destroys the information in the file.  If you want to keep
      it, you can try:

        create a new directory in the same parent directory as the one
        containing the bad file name;

        move everything you can (i.e. everything but the file with the
        bad name) from the old directory to the new one;

        do "ls -id" on the directory containing the file with the bad
        name to get its inumber;

        umount the file system;

        "clri" the directory containing the file with the bad name;

        "fsck" the file system.

      Then, to find the file,

        remount the file system;

        rename the directory you created to have the name of the old
        directory (since the old directory should have been blown away
        by "fsck")

        move the file out of "lost+found" into the directory with a
        better name.

      Alternatively, you can patch the directory the hard way by
      crawling around in the raw file system.  Use "fsdb", if you
      have it.

------------------------------

Subject: How do I get a recursive directory listing?
Date: Thu Mar 18 17:16:55 EST 1993

2.3)  How do I get a recursive directory listing?

      One of the following may do what you want:

        ls -R                   (not all versions of "ls" have -R)
        find . -print           (should work everywhere)
        du -a .                 (shows you both the name and size)

      If you're looking for a wildcard pattern that will match all ".c"
      files in this directory and below, you won't find one, but you
      can use

        % some-command `find . -name '*.c' -print`

      "find" is a powerful program.  Learn about it.

------------------------------

Subject: How do I get the current directory into my prompt?
Date: Thu Mar 18 17:16:55 EST 1993

2.4)  How do I get the current directory into my prompt?

      It depends which shell you are using.  It's easy with some
      shells, hard or impossible with others.

      C Shell (csh):
        Put this in your .cshrc - customize the prompt variable the
        way you want.

            alias setprompt 'set prompt="${cwd}% "'
            setprompt           # to set the initial prompt
            alias cd 'chdir \!* && setprompt'

        If you use pushd and popd, you'll also need

            alias pushd 'pushd \!* && setprompt'
            alias popd  'popd  \!* && setprompt'

        Some C shells don't keep a $cwd variable - you can use
        `pwd` instead.

        If you just want the last component of the current directory
        in your prompt ("mail% " instead of "/usr/spool/mail% ")
        you can use

            alias setprompt 'set prompt="$cwd:t% "'

        Some older csh's get the meaning of && and || reversed.
        Try doing:

            false && echo bug

        If it prints "bug", you need to switch && and || (and get
        a better version of csh.)

      Bourne Shell (sh):

        If you have a newer version of the Bourne Shell (SVR2 or newer)
        you can use a shell function to make your own command, "xcd" say:

            xcd() { cd $* ; PS1="`pwd` $ "; }

        If you have an older Bourne shell, it's complicated but not
        impossible.  Here's one way.  Add this to your .profile file:

                LOGIN_SHELL=$$ export LOGIN_SHELL
                CMDFILE=/tmp/cd.$$ export CMDFILE
                # 16 is SIGURG, pick a signal that's not likely to be used
                PROMPTSIG=16 export PROMPTSIG
                trap '. $CMDFILE' $PROMPTSIG

        and then put this executable script (without the indentation!),
        let's call it "xcd", somewhere in your PATH

                : xcd directory - change directory and set prompt
                : by signalling the login shell to read a command file
                cat >${CMDFILE?"not set"} <<EOF
                cd $1
                PS1="\`pwd\`$ "
                EOF
                kill -${PROMPTSIG?"not set"} ${LOGIN_SHELL?"not set"}

        Now change directories with "xcd /some/dir".

      Korn Shell (ksh):

        Put this in your .profile file:
                PS1='$PWD $ '

        If you just want the last component of the directory, use
                PS1='${PWD##*/} $ '

      T C shell (tcsh)

        Tcsh is a popular enhanced version of csh with some extra
        builtin variables (and many other features):

            %~          the current directory, using ~ for $HOME
            %/          the full pathname of the current directory
            %c or %.    the trailing component of the current directory

        so you can do

            set prompt='%~ '

      BASH (FSF's "Bourne Again SHell")

        \w in $PS1 gives the full pathname of the current directory,
        with ~ expansion for $HOME;  \W gives the basename of
        the current directory.  So, in addition to the above sh and
        ksh solutions, you could use

            PS1='\w $ '
        or
            PS1='\W $ '

------------------------------

Subject: How do I read characters from the terminal in a shell script?
Date: Thu Mar 18 17:16:55 EST 1993

2.5)  How do I read characters from the terminal in a shell script?

      In sh, use read.  It is most common to use a loop like

            while read line
            do
                    ...
            done

      In csh, use $< like this:

            while ( 1 )
                set line = "$<"
                if ( "$line" == "" ) break
                ...
            end

      Unfortunately csh has no way of distinguishing between a blank
      line and an end-of-file.

      If you're using sh and want to read a *single* character from the
      terminal, you can try something like

            echo -n "Enter a character: "
            stty cbreak         # or  stty raw
            readchar=`dd if=/dev/tty bs=1 count=1 2>/dev/null`
            stty -cbreak

            echo "Thank you for typing a $readchar ."

------------------------------

Subject: How do I rename "*.foo" to "*.bar", or change file names to lowercase?
Date: Thu Mar 18 17:16:55 EST 1993

2.6)  How do I rename "*.foo" to "*.bar", or change file names to lowercase?

      Why doesn't "mv *.foo *.bar" work?  Think about how the shell
      expands wildcards.   "*.foo" and "*.bar" are expanded before the
      mv command ever sees the arguments.  Depending on your shell,
      this can fail in a couple of ways.  CSH prints "No match."
      because it can't match "*.bar".  SH executes "mv a.foo b.foo
      c.foo *.bar", which will only succeed if you happen to have a
      single directory named "*.bar", which is very unlikely and almost
      certainly not what you had in mind.

      Depending on your shell, you can do it with a loop to "mv" each
      file individually.  If your system has "basename", you can use:

      C Shell:
        foreach f ( *.foo )
            set base=`basename $f .foo`
            mv $f $base.bar
        end

      Bourne Shell:
        for f in *.foo; do
            base=`basename $f .foo`
            mv $f $base.bar
        done

      Some shells have their own variable substitution features, so
      instead of using "basename", you can use simpler loops like:

      C Shell:

        foreach f ( *.foo )
            mv $f $f:r.bar
        end

      Korn Shell:

        for f in *.foo; do
            mv $f ${f%foo}bar
        done

      If you don't have "basename" or want to do something like
      renaming foo.* to bar.*, you can use something like "sed" to
      strip apart the original file name in other ways, but the general
      looping idea is the same.  You can also convert file names into
      "mv" commands with 'sed', and hand the commands off to "sh" for
      execution.  Try

        ls -d *.foo | sed -e 's/.*/mv & &/' -e 's/foo$/bar/' | sh

      A program by Vladimir Lanin called "mmv" that does this job
      nicely was posted to comp.sources.unix (Volume 21, issues 87 and
      88) in April 1990.  It lets you use

        mmv '*.foo' '=1.bar'

      Shell loops like the above can also be used to translate file
      names from upper to lower case or vice versa.  You could use
      something like this to rename uppercase files to lowercase:

        C Shell:
            foreach f ( * )
                mv $f `echo $f | tr '[A-Z]' '[a-z]'`
            end
        Bourne Shell:
            for f in *; do
                mv $f `echo $f | tr '[A-Z]' '[a-z]'`
            done
        Korn Shell:
            typeset -l l
            for f in *; do
                l="$f"
                mv $f $l
            done

      If you wanted to be really thorough and handle files with `funny'
      names (embedded blanks or whatever) you'd need to use

        Bourne Shell:

            for f in *; do
              g=`expr "xxx$f" : 'xxx\(.*\)' | tr '[A-Z]' '[a-z]'`
              mv "$f" "$g"
            done

      The `expr' command will always print the filename, even if it
      equals `-n' or if it contains a System V escape sequence like `\c'.

      Some versions of "tr" require the [ and ], some don't.  It
      happens to be harmless to include them in this particular
      example; versions of tr that don't want the [] will conveniently
      think they are supposed to translate '[' to '[' and ']' to ']'.

      If you have the "perl" language installed, you may find this
      rename script by Larry Wall very useful.  It can be used to
      accomplish a wide variety of filename changes.

        #!/usr/bin/perl
        #
        # rename script examples from lwall:
        #       rename 's/\.orig$//' *.orig
        #       rename 'y/A-Z/a-z/ unless /^Make/' *
        #       rename '$_ .= ".bad"' *.f
        #       rename 'print "$_: "; s/foo/bar/ if <stdin> =~ /^y/i' *

        $op = shift;
        for (@ARGV) {
            $was = $_;
            eval $op;
            die $@ if $@;
            rename($was,$_) unless $was eq $_;
        }

------------------------------

Subject: Why do I get [some strange error message] when I "rsh host command" ?
Date: Thu Mar 18 17:16:55 EST 1993

2.7)  Why do I get [some strange error message] when I "rsh host command" ?

      (We're talking about the remote shell program "rsh" or sometimes
      "remsh" or "remote"; on some machines, there is a restricted shell
      called "rsh", which is a different thing.)

      If your remote account uses the C shell, the remote host will
      fire up a C shell to execute 'command' for you, and that shell
      will read your remote .cshrc file.  Perhaps your .cshrc contains
      a "stty", "biff" or some other command that isn't appropriate for
      a non-interactive shell.  The unexpected output or error message
      from these commands can screw up your rsh in odd ways.

      Here's an example.  Suppose you have

        stty erase ^H
        biff y

      in your .cshrc file.  You'll get some odd messages like this.

        % rsh some-machine date
        stty: : Can't assign requested address
        Where are you?
        Tue Oct  1 09:24:45 EST 1991

      You might also get similar errors when running certain "at" or
      "cron" jobs that also read your .cshrc file.

      Fortunately, the fix is simple.  There are, quite possibly, a
      whole *bunch* of operations in your ".cshrc" (e.g., "set
      history=N") that are simply not worth doing except in interactive
      shells.  What you do is surround them in your ".cshrc" with:

            if ( $?prompt ) then
                    operations....
            endif

      and, since in a non-interactive shell "prompt" won't be set, the
      operations in question will only be done in interactive shells.

      You may also wish to move some commands to your .login file; if
      those commands only need to be done when a login session starts
      up (checking for new mail, unread news and so on) it's better to
      have them in the .login file.

------------------------------

Subject: How do I ... and have that change affect my current shell?
Date: Thu Mar 18 17:16:55 EST 1993

2.8)  How do I {set an environment variable, change directory} inside
      a program or shell script and have that change affect my
      current shell?

      In general, you can't, at least not without making special
      arrangements.  When a child process is created, it inherits a
      copy of its parent's variables (and current directory).  The
      child can change these values all it wants but the changes won't
      affect the parent shell, since the child is changing a copy of
      the original data.

      Some special arrangements are possible.  Your child process could
      write out the changed variables, if the parent was prepared to
      read the output and interpret it as commands to set its own
      variables.

      Also, shells can arrange to run other shell scripts in the
      context of the current shell, rather than in a child process, so
      that changes will affect the original shell.

      For instance, if you have a C shell script named "myscript":

        cd /very/long/path
        setenv PATH /something:/something-else

      or the equivalent Bourne or Korn shell script

        cd /very/long/path
        PATH=/something:/something-else export PATH

      and try to run "myscript" from your shell, your shell will fork
      and run the shell script in a subprocess.  The subprocess is also
      running the shell; when it sees the "cd" command it changes *its*
      current directory, and when it sees the "setenv" command it
      changes *its* environment, but neither has any effect on the
      current directory of the shell at which you're typing (your login
      shell, let's say).

      In order to get your login shell to execute the script (without
      forking) you have to use the "." command (for the Bourne or Korn
      shells) or the "source" command (for the C shell).  I.e. you type

        . myscript

      to the Bourne or Korn shells, or

        source myscript

      to the C shell.

      If all you are trying to do is change directory or set an
      environment variable, it will probably be simpler to use a C
      shell alias or Bourne/Korn shell function.  See the "how do I get
      the current directory into my prompt" section of this article for
      some examples.

      A much more detailed answer prepared by
      [e-mail] (Thomas Michanek) can be found at
      ftp.wg.omron.co.jp in /pub/unix-faq/docs/script-vs-env.

------------------------------

Subject: How do I redirect stdout and stderr separately in csh?
From: [e-mail] (Mark Brader)
Date: Mon, 26 Oct 1992 20:15:00 -0500

2.9)  How do I redirect stdout and stderr separately in csh?

      In csh, you can redirect stdout with ">", or stdout and stderr
      together with ">&" but there is no direct way to redirect stderr
      only.  The best you can do is

        ( command >stdout_file ) >&stderr_file

      which runs "command" in a subshell;  stdout is redirected inside
      the subshell to stdout_file, and both stdout and stderr from the
      subshell are redirected to stderr_file, but by this point stdout
      has already been redirected so only stderr actually winds up in
      stderr_file.

      If what you want is to avoid redirecting stdout at all, let sh
      do it for you.

        sh -c 'command 2>stderr_file'

------------------------------

Subject: How do I tell inside .cshrc if I'm a login shell?
Date: Thu Mar 18 17:16:55 EST 1993

2.10) How do I tell inside .cshrc if I'm a login shell?

      When people ask this, they usually mean either

        How can I tell if it's an interactive shell?  or
        How can I tell if it's a top-level shell?

      You could perhaps determine if your shell truly is a login shell
      (i.e. is going to source ".login" after it is done with ".cshrc")
      by fooling around with "ps" and "$$".  Login shells generally
      have names that begin with a '-'.  If you're really interested in
      the other two questions, here's one way you can organize your
      .cshrc to find out.

        if (! $?CSHLEVEL) then
                #
                # This is a "top-level" shell,
                # perhaps a login shell, perhaps a shell started up by
                # 'rsh machine some-command'
                # This is where we should set PATH and anything else we
                # want to apply to every one of our shells.
                #
                setenv      CSHLEVEL        0
                set home = ~username        # just to be sure
                source ~/.env               # environment stuff we always want
        else
                #
                # This shell is a child of one of our other shells so
                # we don't need to set all the environment variables again.
                #
                set tmp = $CSHLEVEL
                @ tmp++
                setenv      CSHLEVEL        $tmp
        endif

        # Exit from .cshrc if not interactive, e.g. under rsh
        if (! $?prompt) exit

        # Here we could set the prompt or aliases that would be useful
        # for interactive shells only.

        source ~/.aliases

------------------------------

Subject: How do I construct a ... matches all files except "." and ".." ?
Date: Thu Mar 18 17:16:55 EST 1993

2.11) How do I construct a shell glob-pattern that matches all files
      except "." and ".." ?

      You'd think this would be easy.

      *        Matches all files that don't begin with a ".";

      .*             Matches all files that do begin with a ".", but
             this includes the special entries "." and "..",
             which often you don't want;

      .[!.]*   (Newer shells only; some shells use a "^" instead of
             the "!"; POSIX shells must accept the "!", but may
             accept a "^" as well; all portable applications shall
             not use an unquoted "^" immediately following the "[")

             Matches all files that begin with a "." and are
             followed by a non-"."; unfortunately this will miss
             "..foo";

      .??*     Matches files that begin with a "." and which are
             at least 3 characters long.  This neatly avoids
             "." and "..", but also misses ".a" .

      So to match all files except "." and ".." safely you have to use
      3 patterns (if you don't have filenames like ".a" you can leave
      out the first):

        .[!.]* .??* *

      Alternatively you could employ an external program or two and use
      backquote substitution.  This is pretty good:

      `ls -a | sed -e '/^\.$/d' -e '/^\.\.$/d'`

        (or `ls -A` in some Unix versions)

      but even it will mess up on files with newlines, IFS characters
      or wildcards in their names.

------------------------------

Subject: How do I find the last argument in a Bourne shell script?
Date: Thu Mar 18 17:16:55 EST 1993

2.12) How do I find the last argument in a Bourne shell script?

      Answer by:
        Martin Weitzel <@mikros.systemware.de:[e-mail]>
        Maarten Litmaath <[e-mail]>

      If you are sure the number of arguments is at most 9, you can use:

        eval last=\${$#}

      In POSIX-compatible shells it works for ANY number of arguments.
      The following works always too:

        for last
        do
                :
        done

      This can be generalized as follows:

        for i
        do
                third_last=$second_last
                second_last=$last
                last=$i
        done

      Now suppose you want to REMOVE the last argument from the list,
      or REVERSE the argument list, or ACCESS the N-th argument
      directly, whatever N may be.  Here is a basis of how to do it,
      using only built-in shell constructs, without creating subprocesses:

        t0= u0= rest='1 2 3 4 5 6 7 8 9' argv=

        for h in '' $rest
        do
                for t in "$t0" $rest
                do
                        for u in $u0 $rest
                        do
                                case $# in
                                0)
                                        break 3
                                esac
                                eval argv$h$t$u=\$1
                                argv="$argv \"\$argv$h$t$u\""   # (1)
                                shift
                        done
                        u0=0
                done
                t0=0
        done

        # now restore the arguments
        eval set x "$argv"                                      # (2)
        shift

      This example works for the first 999 arguments.  Enough?
      Take a good look at the lines marked (1) and (2) and convince
      yourself that the original arguments are restored indeed, no
      matter what funny characters they contain!

      To find the N-th argument now you can use this:

        eval argN=\$argv$N

      To reverse the arguments the line marked (1) must be changed to:

        argv="\"\$argv$h$t$u\" $argv"

      How to remove the last argument is left as an exercise.

      If you allow subprocesses as well, possibly executing nonbuilt-in
      commands, the `argvN' variables can be set up more easily:

        N=1

        for i
        do
                eval argv$N=\$i
                N=`expr $N + 1`
        done

      To reverse the arguments there is still a simpler method, that
      even does not create subprocesses.  This approach can also be
      taken if you want to delete e.g. the last argument, but in that
      case you cannot refer directly to the N-th argument any more,
      because the `argvN' variables are set up in reverse order:

        argv=

        for i
        do
                eval argv$#=\$i
                argv="\"\$argv$#\" $argv"
                shift
        done

        eval set x "$argv"
        shift

------------------------------

Subject: What's wrong with having '.' in your $PATH ?
Date: Thu Mar 18 17:16:55 EST 1993

2.13) What's wrong with having '.' in your $PATH ?

      A bit of background: the PATH environment variable is a list of
      directories separated by colons.  When you type a command name
      without giving an explicit path (e.g. you type "ls", rather than
      "/bin/ls") your shell searches each directory in the PATH list in
      order, looking for an executable file by that name, and the shell
      will run the first matching program it finds.

      One of the directories in the PATH list can be the current
      directory "." .  It is also permissible to use an empty directory
      name in the PATH list to indicate the current directory.  Both of
      these are equivalent

      for csh users:

        setenv PATH :/usr/ucb:/bin:/usr/bin
        setenv PATH .:/usr/ucb:/bin:/usr/bin

      for sh or ksh users

        PATH=:/usr/ucb:/bin:/usr/bin export PATH
        PATH=.:/usr/ucb:/bin:/usr/bin export PATH

      Having "." somewhere in the PATH is convenient - you can type
      "a.out" instead of "./a.out" to run programs in the current
      directory.  But there's a catch.

      Consider what happens in the case  where "." is the first entry
      in the PATH.  Suppose your current directory is a publically-
      writable one, such as "/tmp".  If there just happens to be a
      program named "/tmp/ls" left there by some other user, and you
      type "ls" (intending, of course, to run the normal "/bin/ls"
      program), your shell will instead run "./ls", the other user's
      program.  Needless to say, the results of running an unknown
      program like this might surprise you.

      It's slightly better to have "." at the end of the PATH:

        setenv PATH /usr/ucb:/bin:/usr/bin:.

      Now if you're in /tmp and you type "ls", the shell will
      search /usr/ucb, /bin and /usr/bin for a program named
      "ls" before it gets around to looking in ".", and there
      is less risk of inadvertently running some other user's
      "ls" program.  This isn't 100% secure though - if you're
      a clumsy typist and some day type "sl -l" instead of "ls -l",
      you run the risk of running "./sl", if there is one.
      Some "clever" programmer could anticipate common typing
      mistakes and leave programs by those names scattered
      throughout public directories.  Beware.

      Many seasoned Unix users get by just fine without having
      "." in the PATH at all:

        setenv PATH /usr/ucb:/bin:/usr/bin

      If you do this, you'll need to type "./program" instead
      of "program" to run programs in the current directory, but
      the increase in security is probably worth it.

------------------------------

Subject: How do I ring the terminal bell during a shell script?
From: [e-mail] (Uwe Waldmann)
Date: Fri, 30 Apr 93 16:33:00 +0200

2.14) How do I ring the terminal bell during a shell script?

      The answer depends on your Unix version (or rather on the kind of
      "echo" program that is available on your machine).

      A BSD-like "echo" uses the "-n" option for suppressing the final
      newline and does not understand the octal \nnn notation.  Thus
      the command is

        echo -n '^G'

      where ^G means a _literal_ BEL-character (you can produce this in
      emacs using "Ctrl-Q Ctrl-G" and in vi using "Ctrl-V Ctrl-G").

      A SysV-like "echo" understands the \nnn notation and uses \c to
      suppress the final newline, so the answer is:

        echo '\007\c'

------------------------------

Subject: Why can't I use "talk" to talk with my friend on machine X?
From: [e-mail] (Ted Timar)
Date: Thu Mar 18 17:16:55 EST 1993

2.15) Why can't I use "talk" to talk with my friend on machine X?

      Unix has three common "talk" programs, none of which can talk with
      any of the others.  The "old" talk accounts for the first two types.
      This version (often called otalk) did not take "endian" order into
      account when talking to other machines.  As a consequence, the Vax
      version of otalk cannot talk with the Sun version of otalk.
      These versions of talk use port 517.

      Around 1987, most vendors (except Sun, who took 6 years longer than
      any of their competitors) standardized on a new talk (often called
      ntalk) which knows about network byte order.  This talk works between
      all machines that have it.  This version of talk uses port 518.

      There are now a few talk programs that speak both ntalk and one
      version of otalk.  The most common of these is called "ytalk".

------------------------------

Subject: Why does calendar produce the wrong output?
From: [e-mail] (Ted Timar)
Date: Thu Sep  8 09:45:46 EDT 1994

2.16) Why does calendar produce the wrong output?

      Frequently, people find that the output for the Unix calendar
      program, 'cal' produces output that they do not expect.

      The calendar for September 1752 is very odd:

               September 1752
             S  M Tu  W Th  F  S
                   1  2 14 15 16
            17 18 19 20 21 22 23
            24 25 26 27 28 29 30

      This is the month in which the US (the entire British Empire actually)
      switched from the Julian to the Gregorian calendar.

      The other common problem people have with the calendar program is
      that they pass it arguments like 'cal 9 94'.  This gives the calendar
      for September of AD 94, NOT 1994.

------------------------------

End of unix/faq Digest part 2 of 7
**********************************

--
Ted Timar - [e-mail]
ISG Technologies Inc., 6509 Airport Road, Mississauga, Ontario, Canada L4V 1S7
Archive-name: unix-faq/faq/part3
Version: $Id: part3,v 2.5 1994/04/28 19:25:03 tmatimar Exp tmatimar $

These seven articles contain the answers to some Frequently Asked
Questions often seen in comp.unix.questions and comp.unix.shell.
Please don't ask these questions again, they've been answered plenty
of times already - and please don't flame someone just because they may
not have read this particular posting.  Thank you.

This collection of documents is Copyright (c) 1994, Ted Timar, except
Part 6, which is Copyright (c) 1994, Pierre Lewis and Ted Timar.
All rights reserved.  Permission to distribute the collection is
hereby granted providing that distribution is electronic, no money
is involved, reasonable attempts are made to use the latest version
and all credits and this copyright notice are maintained.
Other requests for distribution will be considered.  All reasonable
requests will be granted.

All information here has been contributed with good intentions, but
none of it is guaranteed either by the contributors or myself to be
accurate.  The users of this information take all responsibility for
any damage that may occur.

Many FAQs, including this one, are available on the archive site
rtfm.mit.edu in the directory pub/usenet/news.answers.
The name under which a FAQ is archived appears in the "Archive-Name:"
line at the top of the article.  This FAQ is archived as
"unix-faq/faq/part[1-7]".

These articles are divided approximately as follows:

      1.*) General questions.
      2.*) Relatively basic questions, likely to be asked by beginners.
      3.*) Intermediate questions.
      4.*) Advanced questions, likely to be asked by people who thought
           they already knew all of the answers.
      5.*) Questions pertaining to the various shells, and the differences.
      6.*) An overview of Unix variants.
      7.*) An comparison of configuration management systems (RCS, SCCS).

This article includes answers to:

      3.1)  How do I find the creation time of a file?
      3.2)  How do I use "rsh" without having the rsh hang around
              until the remote command has completed?
      3.3)  How do I truncate a file?
      3.4)  Why doesn't find's "{}" symbol do what I want?
      3.5)  How do I set the permissions on a symbolic link?
      3.6)  How do I "undelete" a file?
      3.7)  How can a process detect if it's running in the background?
      3.8)  Why doesn't redirecting a loop work as intended?  (Bourne shell)
      3.9)  How do I run 'passwd', 'ftp', 'telnet', 'tip' and other interactive
              programs from a shell script or in the background?
      3.10) How do I find the process ID of a program with a particular
            name from inside a shell script or C program?
      3.11) How do I check the exit status of a remote command
            executed via "rsh" ?
      3.12) Is it possible to pass shell variable settings into an awk program?
      3.13) How do I get rid of zombie processes that persevere?
      3.14) How do I get lines from a pipe as they are written instead of
            only in larger blocks.

If you're looking for the answer to, say, question 3.5, and want to skip
everything else, you can search ahead for the regular expression "^3.5)".

While these are all legitimate questions, they seem to crop up in
comp.unix.questions or comp.unix.shell on an annual basis, usually
followed by plenty of replies (only some of which are correct) and then
a period of griping about how the same questions keep coming up.  You
may also like to read the monthly article "Answers to Frequently Asked
Questions" in the newsgroup "news.announce.newusers", which will tell
you what "UNIX" stands for.

With the variety of Unix systems in the world, it's hard to guarantee
that these answers will work everywhere.  Read your local manual pages
before trying anything suggested here.  If you have suggestions or
corrections for any of these answers, please send them to to
[e-mail].

----------------------------------------------------------------------

Subject: How do I find the creation time of a file?
Date: Thu Mar 18 17:16:55 EST 1993

3.1)  How do I find the creation time of a file?

      You can't - it isn't stored anywhere.  Files have a last-modified
      time (shown by "ls -l"), a last-accessed time (shown by "ls -lu")
      and an inode change time (shown by "ls -lc"). The latter is often
      referred to as the "creation time" - even in some man pages -
      but that's wrong; it's also set by such operations as mv, ln,
      chmod, chown and chgrp.

      The man page for "stat(2)" discusses this.

------------------------------

Subject: How do I use "rsh" without having the rsh hang around ... ?
Date: Thu Mar 18 17:16:55 EST 1993

3.2)  How do I use "rsh" without having the rsh hang around until the
      remote command has completed?

      (See note in question 2.7 about what "rsh" we're talking about.)

      The obvious answers fail:
            rsh machine command &
      or      rsh machine 'command &'

      For instance, try doing   rsh machine 'sleep 60 &' and you'll see
      that the 'rsh' won't exit right away.  It will wait 60 seconds
      until the remote 'sleep' command finishes, even though that
      command was started in the background on the remote machine.  So
      how do you get the 'rsh' to exit immediately after the 'sleep' is
      started?

      The solution - if you use csh on the remote machine:

            rsh machine -n 'command >&/dev/null </dev/null &'

      If you use sh on the remote machine:

            rsh machine -n 'command >/dev/null 2>&1 </dev/null &'

      Why?  "-n" attaches rsh's stdin to /dev/null so you could run the
      complete rsh command in the background on the LOCAL machine.
      Thus "-n" is equivalent to another specific "< /dev/null".
      Furthermore, the input/output redirections on the REMOTE machine
      (inside the single quotes) ensure that rsh thinks the session can
      be terminated (there's no data flow any more.)

      Note: The file that you redirect to/from on the remote machine
      doesn't have to be /dev/null; any ordinary file will do.

      In many cases, various parts of these complicated commands
      aren't necessary.

------------------------------

Subject: How do I truncate a file?
Date: Thu Mar 18 17:16:55 EST 1993

3.3)  How do I truncate a file?

      The BSD function ftruncate() sets the length of a file.  Xenix -
      and therefore SysV r3.2 and later - has the chsize() system
      call.  For other systems, the only kind of truncation you can do
      is truncation to length zero with creat() or open(..., O_TRUNC).

------------------------------

Subject: Why doesn't find's "{}" symbol do what I want?
Date: Thu Mar 18 17:16:55 EST 1993

3.4)  Why doesn't find's "{}" symbol do what I want?

      "find" has a -exec option that will execute a particular command
      on all the selected files. Find will replace any "{}" it sees
      with the name of the file currently under consideration.

      So, some day you might try to use "find" to run a command on
      every file, one directory at a time.  You might try this:

        find /path -type d -exec command {}/\* \;

      hoping that find will execute, in turn

        command directory1/*
        command directory2/*
        ...

      Unfortunately, find only expands the "{}" token when it appears
      by itself.  Find will leave anything else like "{}/*" alone, so
      instead of doing what you want, it will do

        command {}/*
        command {}/*
        ...

      once for each directory.  This might be a bug, it might be a
      feature, but we're stuck with the current behaviour.

      So how do you get around this?  One way would be to write a
      trivial little shell script, let's say "./doit", that consists of

        command "$1"/*

      You could then use

        find /path -type d -exec ./doit {} \;

      Or if you want to avoid the "./doit" shell script, you can use

        find /path -type d -exec sh -c 'command $0/*' {} \;

      (This works because within the 'command' of "sh -c 'command' A B C ...",
       $0 expands to A, $1 to B, and so on.)

      or you can use the construct-a-command-with-sed trick

        find /path -type d -print | sed 's:.*:command &/*:' | sh

      If all you're trying to do is cut down on the number of times
      that "command" is executed, you should see if your system has the
      "xargs" command.  Xargs reads arguments one line at a time from
      the standard input and assembles as many of them as will fit into
      one command line.  You could use

        find /path -print | xargs command

      which would result in one or more executions of

        command file1 file2 file3 file4 dir1/file1 dir1/file2

      Unfortunately this is not a perfectly robust or secure solution.
      Xargs expects its input lines to be terminated with newlines, so
      it will be confused by files with odd characters such as newlines
      in their names.

------------------------------

Subject: How do I set the permissions on a symbolic link?
Date: Thu Mar 18 17:16:55 EST 1993

3.5)  How do I set the permissions on a symbolic link?

      Permissions on a symbolic link don't really mean anything.  The
      only permissions that count are the permissions on the file that
      the link points to.

------------------------------

Subject: How do I "undelete" a file?
Date: Thu Mar 18 17:16:55 EST 1993

3.6)  How do I "undelete" a file?

      Someday, you are going to accidentally type something like
      "rm * .foo", and find you just deleted "*" instead of "*.foo".
      Consider it a rite of passage.

      Of course, any decent systems administrator should be doing
      regular backups.  Check with your sysadmin to see if a recent
      backup copy of your file is available.  But if it isn't, read
      on.

      For all intents and purposes, when you delete a file with "rm" it
      is gone.  Once you "rm" a file, the system totally forgets which
      blocks scattered around the disk were part of your file.  Even
      worse, the blocks from the file you just deleted are going to be
      the first ones taken and scribbled upon when the system needs
      more disk space.  However, never say never.  It is theoretically
      possible *if* you shut down the system immediately after the "rm"
      to recover portions of the data.  However, you had better have a
      very wizardly type person at hand with hours or days to spare to
      get it all back.

      Your first reaction when you "rm" a file by mistake is why not
      make a shell alias or procedure which changes "rm" to move files
      into a trash bin rather than delete them?  That way you can
      recover them if you make a mistake, and periodically clean out
      your trash bin.  Two points:  first, this is generally accepted
      as a *bad* idea.  You will become dependent upon this behaviour
      of "rm", and you will find yourself someday on a normal system
      where "rm" is really "rm", and you will get yourself in trouble.
      Second, you will eventually find that the hassle of dealing with
      the disk space and time involved in maintaining the trash bin, it
      might be easier just to be a bit more careful with "rm".  For
      starters, you should look up the "-i" option to "rm" in your
      manual.

      If you are still undaunted, then here is a possible simple
      answer.  You can create yourself a "can" command which moves
      files into a trashcan directory. In csh(1) you can place the
      following commands in the ".login" file in your home directory:

        alias can       'mv \!* ~/.trashcan'       # junk file(s) to trashcan
        alias mtcan     'rm -f ~/.trashcan/*'      # irretrievably empty trash
        if ( ! -d ~/.trashcan ) mkdir ~/.trashcan  # ensure trashcan exists

      You might also want to put a:

        rm -f ~/.trashcan/*

      in the ".logout" file in your home directory to automatically
      empty the trash when you log out.  (sh and ksh versions are left
      as an exercise for the reader.)

      MIT's Project Athena has produced a comprehensive
      delete/undelete/expunge/purge package, which can serve as a
      complete replacement for rm which allows file recovery.  This
      package was posted to comp.sources.misc (volume 17, issue
      023-026)

------------------------------

Subject: How can a process detect if it's running in the background?
Date: Thu Mar 18 17:16:55 EST 1993

3.7)  How can a process detect if it's running in the background?

      First of all: do you want to know if you're running in the
      background, or if you're running interactively? If you're
      deciding whether or not you should print prompts and the like,
      that's probably a better criterion. Check if standard input
      is a terminal:

            sh: if [ -t 0 ]; then ... fi
            C: if(isatty(0)) { ... }

      In general, you can't tell if you're running in the background.
      The fundamental problem is that different shells and different
      versions of UNIX have different notions of what "foreground" and
      "background" mean - and on the most common type of system with a
      better-defined notion of what they mean, programs can be moved
      arbitrarily between foreground and background!

      UNIX systems without job control typically put a process into the
      background by ignoring SIGINT and SIGQUIT and redirecting the
      standard input to "/dev/null"; this is done by the shell.

      Shells that support job control, on UNIX systems that support job
      control, put a process into the background by giving it a process
      group ID different from the process group to which the terminal
      belongs.  They move it back into the foreground by setting the
      terminal's process group ID to that of the process.  Shells that
      do *not* support job control, on UNIX systems that support job
      control, typically do what shells do on systems that don't
      support job control.

------------------------------

Subject: Why doesn't redirecting a loop work as intended?  (Bourne shell)
Date: Thu Mar 18 17:16:55 EST 1993

3.8)  Why doesn't redirecting a loop work as intended?  (Bourne shell)

      Take the following example:

        foo=bar

        while read line
        do
                # do something with $line
                foo=bletch
        done < /etc/passwd

        echo "foo is now: $foo"

      Despite the assignment ``foo=bletch'' this will print
      ``foo is now: bar'' in many implementations of the Bourne shell.
      Why?  Because of the following, often undocumented, feature of
      historic Bourne shells: redirecting a control structure (such as
      a loop, or an ``if'' statement) causes a subshell to be created,
      in which the structure is executed; variables set in that
      subshell (like the ``foo=bletch'' assignment) don't affect the
      current shell, of course.

      The POSIX 1003.2 Shell and Tools Interface standardization
      committee forbids the behaviour described above, i.e. in P1003.2
      conformant Bourne shells the example will print ``foo is now:
      bletch''.

      In historic (and P1003.2 conformant) implementations you can use
      the following `trick' to get around the redirection problem:

        foo=bar

        # make file descriptor 9 a duplicate of file descriptor 0 (stdin);
        # then connect stdin to /etc/passwd; the original stdin is now
        # `remembered' in file descriptor 9; see dup(2) and sh(1)
        exec 9<&0 < /etc/passwd

        while read line
        do
                # do something with $line
                foo=bletch
        done

        # make stdin a duplicate of file descriptor 9, i.e. reconnect
        # it to the original stdin; then close file descriptor 9
        exec 0<&9 9<&-

        echo "foo is now: $foo"

      This should always print ``foo is now: bletch''.
      Right, take the next example:

        foo=bar

        echo bletch | read foo

        echo "foo is now: $foo"

      This will print ``foo is now: bar'' in many implementations,
      ``foo is now: bletch'' in some others.  Why?  Generally each part
      of a pipeline is run in a different subshell; in some
      implementations though, the last command in the pipeline is made
      an exception: if it is a builtin command like ``read'', the
      current shell will execute it, else another subshell is created.

      POSIX 1003.2 allows both behaviours so portable scripts cannot
      depend on any of them.

------------------------------

Subject: How do I run ... interactive programs from a shell script ... ?
Date: Thu Mar 18 17:16:55 EST 1993

3.9)  How do I run 'passwd', 'ftp', 'telnet', 'tip' and other interactive
      programs from a shell script or in the background?

      These programs expect a terminal interface.  Shells makes no
      special provisions to provide one.  Hence, such programs cannot
      be automated in shell scripts.

      The 'expect' program provides a programmable terminal interface
      for automating interaction with such programs.  The following
      expect script is an example of a non-interactive version of
      passwd(1).

        # username is passed as 1st arg, password as 2nd
        set password [index $argv 2]
        spawn passwd [index $argv 1]
        expect "*password:"
        send "$password\r"
        expect "*password:"
        send "$password\r"
        expect eof

      expect can partially automate interaction which is especially
      useful for telnet, rlogin, debuggers or other programs that have
      no built-in command language.  The distribution provides an
      example script to rerun rogue until a good starting configuration
      appears.  Then, control is given back to the user to enjoy the game.

      Fortunately some programs have been written to manage the
      connection to a pseudo-tty so that you can run these sorts of
      programs in a script.

      To get expect, email "send pub/expect/expect.shar.Z" to
      [e-mail] or anonymous ftp same from
      ftp.cme.nist.gov.

      Another solution is provided by the pty 4.0 program, which runs a
      program under a pseudo-tty session and was posted to
      comp.sources.unix, volume 25.  A pty-based solution using named
      pipes to do the same as the above might look like this:

        #!/bin/sh
        /etc/mknod out.$$ p; exec 2>&1
        ( exec 4<out.$$; rm -f out.$$
        <&4 waitfor 'password:'
            echo "$2"
        <&4 waitfor 'password:'
            echo "$2"
        <&4 cat >/dev/null
        ) | ( pty passwd "$1" >out.$$ )

      Here, 'waitfor' is a simple C program that searches for
      its argument in the input, character by character.

      A simpler pty solution (which has the drawback of not
      synchronizing properly with the passwd program) is

        #!/bin/sh
        ( sleep 5; echo "$2"; sleep 5; echo "$2") | pty passwd "$1"

------------------------------

Subject: How do I find the process ID of a program with a particular name ... ?
Date: Thu Mar 18 17:16:55 EST 1993

3.10) How do I find the process ID of a program with a particular name
      from inside a shell script or C program?

      In a shell script:

      There is no utility specifically designed to map between program
      names and process IDs.  Furthermore, such mappings are often
      unreliable, since it's possible for more than one process to have
      the same name, and since it's possible for a process to change
      its name once it starts running.  However, a pipeline like this
      can often be used to get a list of processes (owned by you) with
      a particular name:

            ps ux | awk '/name/ && !/awk/ {print $2}'

      You replace "name" with the name of the process for which you are
      searching.

      The general idea is to parse the output of ps, using awk or grep
      or other utilities, to search for the lines with the specified
      name on them, and print the PID's for those lines.  Note that the
      "!/awk/" above prevents the awk process for being listed.

      You may have to change the arguments to ps, depending on what
      kind of Unix you are using.

      In a C program:

      Just as there is no utility specifically designed to map between
      program names and process IDs, there are no (portable) C library
      functions to do it either.

      However, some vendors provide functions for reading Kernel
      memory; for example, Sun provides the "kvm_" functions, and Data
      General provides the "dg_" functions.  It may be possible for any
      user to use these, or they may only be useable by the super-user
      (or a user in group "kmem") if read-access to kernel memory on
      your system is restricted.  Furthermore, these functions are
      often not documented or documented badly, and might change from
      release to release.

      Some vendors provide a "/proc" filesystem, which appears as a
      directory with a bunch of filenames in it.  Each filename is a
      number, corresponding to a process ID, and you can open the file
      and read it to get information about the process.  Once again,
      access to this may be restricted, and the interface to it may
      change from system to system.

      If you can't use vendor-specific library functions, and you
      don't have /proc, and you still want to do this completely
      in C, you
      are going to have to do the rummaging through kernel memory
      yourself.  For a good example of how to do this on many systems,
      see the sources to "ofiles", available in the comp.sources.unix
      archives.  (A package named "kstuff" to help with kernel
      rummaging was posted to alt.sources in May 1991 and is also
      available via anonymous ftp as
      usenet/alt.sources/articles/{329{6,7,8,9},330{0,1}}.Z from
      wuarchive.wustl.edu.)

------------------------------

Subject: How do I check the exit status of a remote command executed via "rsh"?
Date: Thu Mar 18 17:16:55 EST 1993

3.11) How do I check the exit status of a remote command
      executed via "rsh" ?

      This doesn't work:

        rsh some-machine some-crummy-command || echo "Command failed"

      The exit status of 'rsh' is 0 (success) if the rsh program
      itself completed successfully, which probably isn't what
      you wanted.

      If you want to check on the exit status of the remote program,
      you can try using Maarten Litmaath's 'ersh' script, which was
      posted to alt.sources in January, 1991.  ersh is a shell script
      that calls rsh, arranges for the remote machine to echo the
      status of the command after it completes, and exits with that
      status.

------------------------------

Subject: Is it possible to pass shell variable settings into an awk program?
Date: Thu Mar 18 17:16:55 EST 1993

3.12) Is it possible to pass shell variable settings into an awk program?

      There are two different ways to do this.  The first involves
      simply expanding the variable where it is needed in the program.
      For example, to get a list of all ttys you're using:

        who | awk '/^'"$USER"'/ { print $2 }'                           (1)

      Single quotes are usually used to enclose awk programs because
      the character '$' is often used in them, and '$' will be
      interpreted by the shell if enclosed inside double quotes, but
      not if enclosed inside single quotes.  In this case, we *want*
      the '$' in "$USER" to be interpreted by the shell, so we close
      the single quotes and then put the "$USER" inside double quotes.
      Note that there are no spaces in any of that, so the shell will
      see it all as one argument.  Note, further, that the double
      quotes probably aren't necessary in this particular case (i.e. we
      could have done

        who | awk '/^'$USER'/ { print $2 }'                             (2)

      ), but they should be included nevertheless because they are
      necessary when the shell variable in question contains special
      characters or spaces.

      The second way to pass variable settings into awk is to use an
      often undocumented feature of awk which allows variable settings
      to be specified as "fake file names" on the command line.  For
      example:

        who | awk '$1 == user { print $2 }' user="$USER" -              (3)

      Variable settings take effect when they are encountered on the
      command line, so, for example, you could instruct awk on how to
      behave for different files using this technique.  For example:

        awk '{ program that depends on s }' s=1 file1 s=0 file2         (4)

      Note that some versions of awk will cause variable settings
      encountered before any real filenames to take effect before the
      BEGIN block is executed, but some won't so neither way should be
      relied upon.

      Note, further, that when you specify a variable setting, awk
      won't automatically read from stdin if no real files are
      specified, so you need to add a "-" argument to the end of your
      command, as I did at (3) above.

------------------------------

Subject: How do I get rid of zombie processes that persevere?
From: [e-mail] (Jonathan I. Kamens)
From: [e-mail] (Casper Dik)
Date: Thu, 09 Sep 93 16:39:58 +0200

3.13) How do I get rid of zombie processes that persevere?

      Unfortunately, it's impossible to generalize how the death of
      child processes should behave, because the exact mechanism varies
      over the various flavors of Unix.

      First of all, by default, you have to do a wait() for child
      processes under ALL flavors of Unix.  That is, there is no flavor
      of Unix that I know of that will automatically flush child
      processes that exit, even if you don't do anything to tell it to
      do so.

      Second, under some SysV-derived systems, if you do
      "signal(SIGCHLD, SIG_IGN)" (well, actually, it may be SIGCLD
      instead of SIGCHLD, but most of the newer SysV systems have
      "#define SIGCHLD SIGCLD" in the header files), then child
      processes will be cleaned up automatically, with no further
      effort in your part.  The best way to find out if it works at
      your site is to try it, although if you are trying to write
      portable code, it's a bad idea to rely on this in any case.
      Unfortunately, POSIX doesn't allow you to do this; the behavior
      of setting the SIGCHLD to SIG_IGN under POSIX is undefined, so
      you can't do it if your program is supposed to be
      POSIX-compliant.

      So, what's the POSIX way? As mentioned earlier, you must
      install a signal handler and wait. Under POSIX signal handlers
      are installed with sigaction. Since you are not interested in
      ``stopped'' children, only in terminated children, add SA_NOCLDSTOP
      to sa_flags.  Waiting without blocking is done with waitpid().
      The first argument to waitpid should be -1 (wait for any pid),
      the third should be WNOHANG. This is the most portable way
      and is likely to become more portable in future.

      If your systems doesn't support POSIX, there's a number of ways.
      The easiest way is signal(SIGCHLD, SIG_IGN), if it works.
      If SIG_IGN cannot be used to force automatic clean-up, then you've
      got to write a signal handler to do it.  It isn't easy at all to
      write a signal handler that does things right on all flavors of
      Unix, because of the following inconsistencies:

      On some flavors of Unix, the SIGCHLD signal handler is called if
      one *or more* children have died.  This means that if your signal
      handler only does one wait() call, then it won't clean up all of
      the children.  Fortunately, I believe that all Unix flavors for
      which this is the case have available to the programmer the
      wait3() or waitpid() call, which allows the WNOHANG option to
      check whether or not there are any children waiting to be cleaned
      up.  Therefore, on any system that has wait3()/waitpid(), your
      signal handler should call wait3()/waitpid() over and over again
      with the WNOHANG option until there are no children left to clean
      up. Waitpid() is the preferred interface, as it is in POSIX.

      On SysV-derived systems, SIGCHLD signals are regenerated if there
      are child processes still waiting to be cleaned up after you exit
      the SIGCHLD signal handler.  Therefore, it's safe on most SysV
      systems to assume when the signal handler gets called that you
      only have to clean up one signal, and assume that the handler
      will get called again if there are more to clean up after it
      exits.

      On older systems, there is no way to prevent signal handlers
      from being automatically reset to SIG_DFL when the signal
      handler gets called.  On such systems, you have to put
      "signal(SIGCHILD, catcher_func)" (where "catcher_func" is the
      name of the handler function) as the last thing in the signal
      handler, so that it gets reset.

      Fortunately, newer implementations allow signal handlers to be
      installed without being reset to SIG_DFL when the handler
      function is called.  To get around this problem, on systems that
      do not have wait3()/waitpid() but do have SIGCLD, you need to
      reset the signal handler with a call to signal() after doing at
      least one wait() within the handler, each time it is called.  For
      backward compatibility reasons, System V will keep the old
      semantics (reset handler on call) of signal().  Signal handlers
      that stick can be installed with sigaction() or sigset().

      The summary of all this is that on systems that have waitpid()
      (POSIX) or wait3(), you should use that and your signal handler
      should loop, and on systems that don't, you should have one call
      to wait() per invocation of the signal handler.

      One more thing -- if you don't want to go through all of this
      trouble, there is a portable way to avoid this problem, although
      it is somewhat less efficient.  Your parent process should fork,
      and then wait right there and then for the child process to
      terminate.  The child process then forks again, giving you a
      child and a grandchild.  The child exits immediately (and hence
      the parent waiting for it notices its death and continues to
      work), and the grandchild does whatever the child was originally
      supposed to.  Since its parent died, it is inherited by init,
      which will do whatever waiting is needed.  This method is
      inefficient because it requires an extra fork, but is pretty much
      completely portable.

------------------------------

Subject: How do I get lines from a pipe ... instead of only in larger blocks?
From: [e-mail] (Jonathan I. Kamens)
Date: Sun, 16 Feb 92 20:59:28 -0500

3.14) How do I get lines from a pipe as they are written instead of only in
      larger blocks?

      The stdio library does buffering differently depending on whether
      it thinks it's running on a tty.  If it thinks it's on a tty, it
      does buffering on a per-line basis; if not, it uses a larger
      buffer than one line.

      If you have the source code to the client whose buffering you
      want to disable, you can use setbuf() or setvbuf() to change the
      buffering.

      If not, the best you can do is try to convince the program that
      it's running on a tty by running it under a pty, e.g. by using
      the "pty" program mentioned in question 3.9.

------------------------------

End of unix/faq Digest part 3 of 7
**********************************

--
Ted Timar - [e-mail]
ISG Technologies Inc., 6509 Airport Road, Mississauga, Ontario, Canada L4V 1S7
Archive-name: unix-faq/faq/part4
Version: $Id: part4,v 2.5 1994/04/28 19:25:03 tmatimar Exp tmatimar $

These seven articles contain the answers to some Frequently Asked
Questions often seen in comp.unix.questions and comp.unix.shell.
Please don't ask these questions again, they've been answered plenty
of times already - and please don't flame someone just because they may
not have read this particular posting.  Thank you.

This collection of documents is Copyright (c) 1994, Ted Timar, except
Part 6, which is Copyright (c) 1994, Pierre Lewis and Ted Timar.
All rights reserved.  Permission to distribute the collection is
hereby granted providing that distribution is electronic, no money
is involved, reasonable attempts are made to use the latest version
and all credits and this copyright notice are maintained.
Other requests for distribution will be considered.  All reasonable
requests will be granted.

All information here has been contributed with good intentions, but
none of it is guaranteed either by the contributors or myself to be
accurate.  The users of this information take all responsibility for
any damage that may occur.

Many FAQs, including this one, are available on the archive site
rtfm.mit.edu in the directory pub/usenet/news.answers.
The name under which a FAQ is archived appears in the "Archive-Name:"
line at the top of the article.  This FAQ is archived as
"unix-faq/faq/part[1-7]".

These articles are divided approximately as follows:

      1.*) General questions.
      2.*) Relatively basic questions, likely to be asked by beginners.
      3.*) Intermediate questions.
      4.*) Advanced questions, likely to be asked by people who thought
           they already knew all of the answers.
      5.*) Questions pertaining to the various shells, and the differences.
      6.*) An overview of Unix variants.
      7.*) An comparison of configuration management systems (RCS, SCCS).

This article includes answers to:

      4.1)  How do I read characters from a terminal without requiring the user
              to hit RETURN?
      4.2)  How do I check to see if there are characters to be read without
              actually reading?
      4.3)  How do I find the name of an open file?
      4.4)  How can an executing program determine its own pathname?
      4.5)  How do I use popen() to open a process for reading AND writing?
      4.6)  How do I sleep() in a C program for less than one second?
      4.7)  How can I get setuid shell scripts to work?
      4.8)  How can I find out which user or process has a file open or is using
            a particular file system (so that I can unmount it?)
      4.9)  How do I keep track of people who are fingering me?
      4.10) Is it possible to reconnect a process to a terminal after it has
            been disconnected, e.g. after starting a program in the background
            and logging out?
      4.11) Is it possible to "spy" on a terminal, displaying the output
            that's appearing on it on another terminal?

If you're looking for the answer to, say, question 4.5, and want to skip
everything else, you can search ahead for the regular expression "^4.5)".

While these are all legitimate questions, they seem to crop up in
comp.unix.questions or comp.unix.shell on an annual basis, usually
followed by plenty of replies (only some of which are correct) and then
a period of griping about how the same questions keep coming up.  You
may also like to read the monthly article "Answers to Frequently Asked
Questions" in the newsgroup "news.announce.newusers", which will tell
you what "UNIX" stands for.

With the variety of Unix systems in the world, it's hard to guarantee
that these answers will work everywhere.  Read your local manual pages
before trying anything suggested here.  If you have suggestions or
corrections for any of these answers, please send them to to
[e-mail].

----------------------------------------------------------------------

Subject: How do I read characters ... without requiring the user to hit RETURN?
Date: Thu Mar 18 17:16:55 EST 1993

4.1)  How do I read characters from a terminal without requiring the user
      to hit RETURN?

      Check out cbreak mode in BSD, ~ICANON mode in SysV.

      If you don't want to tackle setting the terminal parameters
      yourself (using the "ioctl(2)" system call) you can let the stty
      program do the work - but this is slow and inefficient, and you
      should change the code to do it right some time:

      #include <stdio.h>
      main()
      {
            int c;

            printf("Hit any character to continue\n");
            /*
             * ioctl() would be better here; only lazy
             * programmers do it this way:
             */
            system("/bin/stty cbreak");        /* or "stty raw" */
            c = getchar();
            system("/bin/stty -cbreak");
            printf("Thank you for typing %c.\n", c);

            exit(0);
      }

      Several people have sent me various more correct solutions to
      this problem.  I'm sorry that I'm not including any of them here,
      because they really are beyond the scope of this list.

      You might like to check out the documentation for the "curses"
      library of portable screen functions.  Often if you're interested
      in single-character I/O like this, you're also interested in
      doing some sort of screen display control, and the curses library
      provides various portable routines for both functions.

------------------------------

Subject: How do I check to see if there are characters to be read ... ?
Date: Thu Mar 18 17:16:55 EST 1993

4.2)  How do I check to see if there are characters to be read without
      actually reading?

      Certain versions of UNIX provide ways to check whether characters
      are currently available to be read from a file descriptor.  In
      BSD, you can use select(2).  You can also use the FIONREAD ioctl
      (see tty(4)), which returns the number of characters waiting to
      be read, but only works on terminals, pipes and sockets.  In
      System V Release 3, you can use poll(2), but that only works on
      streams.  In Xenix - and therefore Unix SysV r3.2 and later - the
      rdchk() system call reports whether a read() call on a given file
      descriptor will block.

      There is no way to check whether characters are available to be
      read from a FILE pointer.  (You could poke around inside stdio
      data structures to see if the input buffer is nonempty, but that
      wouldn't work since you'd have no way of knowing what will happen
      the next time you try to fill the buffer.)

      Sometimes people ask this question with the intention of writing
            if (characters available from fd)
                    read(fd, buf, sizeof buf);
      in order to get the effect of a nonblocking read.  This is not
      the best way to do this, because it is possible that characters
      will be available when you test for availability, but will no
      longer be available when you call read.  Instead, set the
      O_NDELAY flag (which is also called FNDELAY under BSD) using the
      F_SETFL option of fcntl(2).  Older systems (Version 7, 4.1 BSD)
      don't have O_NDELAY; on these systems the closest you can get to
      a nonblocking read is to use alarm(2) to time out the read.

------------------------------

Subject: How do I find the name of an open file?
Date: Thu Mar 18 17:16:55 EST 1993

4.3)  How do I find the name of an open file?

      In general, this is too difficult.  The file descriptor may
      be attached to a pipe or pty, in which case it has no name.
      It may be attached to a file that has been removed.  It may
      have multiple names, due to either hard or symbolic links.

      If you really need to do this, and be sure you think long
      and hard about it and have decided that you have no choice,
      you can use find with the -inum and possibly -xdev option,
      or you can use ncheck, or you can recreate the functionality
      of one of these within your program.  Just realize that
      searching a 600 megabyte filesystem for a file that may not
      even exist is going to take some time.

------------------------------

Subject: How can an executing program determine its own pathname?
Date: Thu Mar 18 17:16:55 EST 1993

4.4)  How can an executing program determine its own pathname?

      Your program can look at argv[0]; if it begins with a "/", it is
      probably the absolute pathname to your program, otherwise your
      program can look at every directory named in the environment
      variable PATH and try to find the first one that contains an
      executable file whose name matches your program's argv[0] (which
      by convention is the name of the file being executed).  By
      concatenating that directory and the value of argv[0] you'd
      probably have the right name.

      You can't really be sure though, since it is quite legal for one
      program to exec() another with any value of argv[0] it desires.
      It is merely a convention that new programs are exec'd with the
      executable file name in argv[0].

      For instance, purely a hypothetical example:

        #include <stdio.h>
        main()
        {
            execl("/usr/games/rogue", "vi Thesis", (char *)NULL);
        }

      The executed program thinks its name (its argv[0] value) is
      "vi Thesis".   (Certain other programs might also think that
      the name of the program you're currently running is "vi Thesis",
      but of course this is just a hypothetical example, don't
      try it yourself :-)

------------------------------

Subject: How do I use popen() to open a process for reading AND writing?
Date: Thu Mar 18 17:16:55 EST 1993

4.5)  How do I use popen() to open a process for reading AND writing?

      The problem with trying to pipe both input and output to an
      arbitrary slave process is that deadlock can occur, if both
      processes are waiting for not-yet-generated input at the same
      time.  Deadlock can be avoided only by having BOTH sides follow a
      strict deadlock-free protocol, but since that requires
      cooperation from the processes it is inappropriate for a
      popen()-like library function.

      The 'expect' distribution includes a library of functions that a
      C programmer can call directly.  One of the functions does the
      equivalent of a popen for both reading and writing.  It uses ptys
      rather than pipes, and has no deadlock problem.  It's portable to
      both BSD and SV.  See the next answer for more about 'expect'.

------------------------------

Subject: How do I sleep() in a C program for less than one second?
Date: Thu Mar 18 17:16:55 EST 1993

4.6)  How do I sleep() in a C program for less than one second?

      The first thing you need to be aware of is that all you can
      specify is a MINIMUM amount of delay; the actual delay will
      depend on scheduling issues such as system load, and could be
      arbitrarily large if you're unlucky.

      There is no standard library function that you can count on in
      all environments for "napping" (the usual name for short
      sleeps).  Some environments supply a "usleep(n)" function which
      suspends execution for n microseconds.  If your environment
      doesn't support usleep(), here are a couple of implementations
      for BSD and System V environments.

      The following code is adapted from Doug Gwyn's System V emulation
      support for 4BSD and exploits the 4BSD select() system call.
      Doug originally called it 'nap()'; you probably want to call it
      "usleep()";

      /*
            usleep -- support routine for 4.2BSD system call emulations
            last edit:  29-Oct-1984     D A Gwyn
      */

      extern int        select();

      int
      usleep( usec )                            /* returns 0 if ok, else -1 */
            long                usec;           /* delay in microseconds */
            {
            static struct                       /* `timeval' */
                    {
                    long        tv_sec;         /* seconds */
                    long        tv_usec;        /* microsecs */
                    }   delay;          /* _select() timeout */

            delay.tv_sec = usec / 1000000L;
            delay.tv_usec = usec % 1000000L;

            return select( 0, (long *)0, (long *)0, (long *)0, &delay );
            }

      On System V you might do it this way:

      /*
      subseconds sleeps for System V - or anything that has poll()
      Don Libes, 4/1/1991

      The BSD analog to this function is defined in terms of
      microseconds while poll() is defined in terms of milliseconds.
      For compatibility, this function provides accuracy "over the long
      run" by truncating actual requests to milliseconds and
      accumulating microseconds across calls with the idea that you are
      probably calling it in a tight loop, and that over the long run,
      the error will even out.

      If you aren't calling it in a tight loop, then you almost
      certainly aren't making microsecond-resolution requests anyway,
      in which case you don't care about microseconds.  And if you did,
      you wouldn't be using UNIX anyway because random system
      indigestion (i.e., scheduling) can make mincemeat out of any
      timing code.

      Returns 0 if successful timeout, -1 if unsuccessful.

      */

      #include <poll.h>

      int
      usleep(usec)
      unsigned int usec;                /* microseconds */
      {
            static subtotal = 0;        /* microseconds */
            int msec;                   /* milliseconds */

            /* 'foo' is only here because some versions of 5.3 have
             * a bug where the first argument to poll() is checked
             * for a valid memory address even if the second argument is 0.
             */
            struct pollfd foo;

            subtotal += usec;
            /* if less then 1 msec request, do nothing but remember it */
            if (subtotal < 1000) return(0);
            msec = subtotal/1000;
            subtotal = subtotal%1000;
            return poll(&foo,(unsigned long)0,msec);
      }

      Another possibility for nap()ing on System V, and probably other
      non-BSD Unices is Jon Zeeff's s5nap package, posted to
      comp.sources.misc, volume 4.  It does require a installing a
      device driver, but works flawlessly once installed.  (Its
      resolution is limited to the kernel HZ value, since it uses the
      kernel delay() routine.)

------------------------------

Subject: How can I get setuid shell scripts to work?
Date: Thu Mar 18 17:16:55 EST 1993

4.7)  How can I get setuid shell scripts to work?

      [ This is a long answer, but it's a complicated and frequently-asked
        question.  Thanks to Maarten Litmaath for this answer, and
        for the "indir" program mentioned below. ]

      Let us first assume you are on a UNIX variant (e.g. 4.3BSD or
      SunOS) that knows about so-called `executable shell scripts'.
      Such a script must start with a line like:

        #!/bin/sh

      The script is called `executable' because just like a real (binary)
      executable it starts with a so-called `magic number' indicating
      the type of the executable.  In our case this number is `#!' and
      the OS takes the rest of the first line as the interpreter for
      the script, possibly followed by 1 initial option like:

        #!/bin/sed -f

      Suppose this script is called `foo' and is found in /bin,
      then if you type:

        foo arg1 arg2 arg3

      the OS will rearrange things as though you had typed:

        /bin/sed -f /bin/foo arg1 arg2 arg3

      There is one difference though: if the setuid permission bit for
      `foo' is set, it will be honored in the first form of the
      command; if you really type the second form, the OS will honor
      the permission bits of /bin/sed, which is not setuid, of course.

      ----------

      OK, but what if my shell script does NOT start with such a `#!'
      line or my OS does not know about it?

      Well, if the shell (or anybody else) tries to execute it, the OS
      will return an error indication, as the file does not start with
      a valid magic number.  Upon receiving this indication the shell
      ASSUMES the file to be a shell script and gives it another try:

        /bin/sh shell_script arguments

      But we have already seen that a setuid bit on `shell_script' will
      NOT be honored in this case!

      ----------

      Right, but what about the security risks of setuid shell scripts?

      Well, suppose the script is called `/etc/setuid_script', starting
      with:

        #!/bin/sh

      Now let us see what happens if we issue the following commands:

        $ cd /tmp
        $ ln /etc/setuid_script -i
        $ PATH=.
        $ -i

      We know the last command will be rearranged to:

        /bin/sh -i

      But this command will give us an interactive shell, setuid to the
      owner of the script!
      Fortunately this security hole can easily be closed by making the
      first line:

        #!/bin/sh -

      The `-' signals the end of the option list: the next argument `-i'
      will be taken as the name of the file to read commands from, just
      like it should!

      ---------

      There are more serious problems though:

        $ cd /tmp
        $ ln /etc/setuid_script temp
        $ nice -20 temp &
        $ mv my_script temp

      The third command will be rearranged to:

        nice -20 /bin/sh - temp

      As this command runs so slowly, the fourth command might be able
      to replace the original `temp' with `my_script' BEFORE `temp' is
      opened by the shell!  There are 4 ways to fix this security hole:

        1)  let the OS start setuid scripts in a different, secure way
            - System V R4 and 4.4BSD use the /dev/fd driver to pass the
            interpreter a file descriptor for the script

        2)  let the script be interpreted indirectly, through a frontend
            that makes sure everything is all right before starting the
            real interpreter - if you use the `indir' program from
            comp.sources.unix the setuid script will look like this:

                #!/bin/indir -u
                #?/bin/sh /etc/setuid_script

        3)  make a `binary wrapper': a real executable that is setuid and
            whose only task is to execute the interpreter with the name of
            the script as an argument

        4)  make a general `setuid script server' that tries to locate the
            requested `service' in a database of valid scripts and upon
            success will start the right interpreter with the right
            arguments.

      ---------

      Now that we have made sure the right file gets interpreted, are
      there any risks left?

      Certainly!  For shell scripts you must not forget to set the PATH
      variable to a safe path explicitly.  Can you figure out why?
      Also there is the IFS variable that might cause trouble if not
      set properly.  Other environment variables might turn out to
      compromise security as well, e.g. SHELL...  Furthermore you must
      make sure the commands in the script do not allow interactive
      shell escapes!  Then there is the umask which may have been set
      to something strange...

      Etcetera.  You should realise that a setuid script `inherits' all
      the bugs and security risks of the commands that it calls!

      All in all we get the impression setuid shell scripts are quite a
      risky business!  You may be better off writing a C program instead!

------------------------------

Subject: How can I find out which user or process has a file open ... ?
Date: Thu Mar 18 17:16:55 EST 1993

4.8)  How can I find out which user or process has a file open or is using
      a particular file system (so that I can unmount it?)

      Use fuser (system V), fstat (BSD), ofiles (public domain) or
      pff (public domain).  These programs will tell you various things
      about processes using particular files.

      A port of the 4.3 BSD fstat to Dynix, SunOS and Ultrix
      can be found in archives of comp.sources.unix, volume 18.

      pff is part of the kstuff package, and works on quite a few systems.
      Instructions for obtaining kstuff are provided in question 3.10.

------------------------------

Subject: How do I keep track of people who are fingering me?
From: [e-mail] (Jonathan I. Kamens)
From: [e-mail] (Nikola Malenovic)
Date: Mon, 23 Nov 1992 16:01:45 -0600

4.9)  How do I keep track of people who are fingering me?

      Generally, you can't find out the userid of someone who is
      fingering you from a remote machine.  You may be able to
      find out which machine the remote request is coming from.
      One possibility, if your system supports it and assuming
      the finger daemon doesn't object, is to make your .plan file a
      "named pipe" instead of a plain file.  (Use 'mknod' to do this.)

      You can then start up a program that will open your .plan file
      for writing; the open will block until some other process (namely
      fingerd) opens the .plan for reading.  Now you can whatever you
      want through this pipe, which lets you show different .plan
      information every time someone fingers you.

      Of course, this may not work at all if your system doesn't
      support named pipes or if your local fingerd insists
      on having plain .plan files.

      Your program can also take the opportunity to look at the output
      of "netstat" and spot where an incoming finger connection is
      coming from, but this won't get you the remote user.

      Getting the remote userid would require that the remote site be
      running an identity service such as RFC 931.  There are now three
      RFC 931 implementations for popular BSD machines, and several
      applications (such as the wuarchive ftpd) supporting the server.
      For more information join the rfc931-users mailing list,
      [e-mail].

      There are three caveats relating to this answer.  The first is
      that many NFS systems won't recognize the named pipe correctly.
      This means that trying to read the pipe on another machine will
      either block until it times out, or see it as a zero-length file,
      and never print it.

      The second problem is that on many systems, fingerd checks that
      the .plan file contains data (and is readable) before trying to
      read it.  This will cause remote fingers to miss your .plan file
      entirely.

      The third problem is that a system that supports named pipes
      usually has a fixed number of named pipes available on the
      system at any given time - check the kernel config file and
      FIFOCNT option.  If the number of pipes on the system exceeds the
      FIFOCNT value, the system blocks new pipes until somebody frees
      the resources.  The reason for this is that buffers are allocated
      in a non-paged memory.

------------------------------

Subject: Is it possible to reconnect a process to a terminal ... ?
Date: Thu Mar 18 17:16:55 EST 1993

4.10) Is it possible to reconnect a process to a terminal after it has
      been disconnected, e.g. after starting a program in the background
      and logging out?

      Most variants of Unix do not support "detaching" and "attaching"
      processes, as operating systems such as VMS and Multics support.
      However, there are two freely redistributable packages which can
      be used to start processes in such a way that they can be later
      reattached to a terminal.

      The first is "screen," which is described in the
      comp.sources.unix archives as "Screen, multiple windows on a CRT"
      (see the "screen-3.2" package in comp.sources.misc, volume 28.)
      This package will run on at least BSD, System V r3.2 and SCO UNIX.

      The second is "pty," which is described in the comp.sources.unix
      archives as a package to "Run a program under a pty session" (see
      "pty" in volume 23).  pty is designed for use under BSD-like
      system only.

      Neither of these packages is retroactive, i.e. you must have
      started a process under screen or pty in order to be able to
      detach and reattach it.

------------------------------

Subject: Is it possible to "spy" on a terminal ... ?
Date: Thu Mar 18 17:16:55 EST 1993

4.11) Is it possible to "spy" on a terminal, displaying the output
      that's appearing on it on another terminal?

      There are a few different ways you can do this, although none
      of them is perfect:

      * kibitz allows two (or more) people to interact with a shell
        (or any arbitary program).  Uses include:

        - watching or aiding another person's terminal session;
        - recording a conversation while retaining the ability to
          scroll backwards, save the conversation, or even edit it
          while in progress;
        - teaming up on games, document editing, or other cooperative
          tasks where each person has strengths and weakness that
          complement one another.

        kibitz comes as part of the expect distribution.  See question 3.9.

        kibitz requires permission from the person to be spyed upon.  To
        spy without permission requires less pleasant approaches:

      * You can write a program that rummages through Kernel structures
        and watches the output buffer for the terminal in question,
        displaying characters as they are output.  This, obviously, is
        not something that should be attempted by anyone who does not
        have experience working with the Unix kernel.  Furthermore,
        whatever method you come up with will probably be quite
        non-portable.

      * If you want to do this to a particular hard-wired terminal all
        the time (e.g. if you want operators to be able to check the
        console terminal of a machine from other machines), you can
        actually splice a monitor into the cable for the terminal.  For
        example, plug the monitor output into another machine's serial
        port, and run a program on that port that stores its input
        somewhere and then transmits it out *another* port, this one
        really going to the physical terminal.  If you do this, you have
        to make sure that any output from the terminal is transmitted
        back over the wire, although if you splice only into the
        computer->terminal wires, this isn't much of a problem.  This is
        not something that should be attempted by anyone who is not very
        familiar with terminal wiring and such.

------------------------------

End of unix/faq Digest part 4 of 7
**********************************

--
Ted Timar - [e-mail]
ISG Technologies Inc., 6509 Airport Road, Mississauga, Ontario, Canada L4V 1S7
Archive-name: unix-faq/faq/part5
Version: $Id: part5,v 2.5 1994/04/28 19:25:03 tmatimar Exp tmatimar $

These seven articles contain the answers to some Frequently Asked
Questions often seen in comp.unix.questions and comp.unix.shell.
Please don't ask these questions again, they've been answered plenty
of times already - and please don't flame someone just because they may
not have read this particular posting.  Thank you.

This collection of documents is Copyright (c) 1994, Ted Timar, except
Part 6, which is Copyright (c) 1994, Pierre Lewis and Ted Timar.
All rights reserved.  Permission to distribute the collection is
hereby granted providing that distribution is electronic, no money
is involved, reasonable attempts are made to use the latest version
and all credits and this copyright notice are maintained.
Other requests for distribution will be considered.  All reasonable
requests will be granted.

All information here has been contributed with good intentions, but
none of it is guaranteed either by the contributors or myself to be
accurate.  The users of this information take all responsibility for
any damage that may occur.

Many FAQs, including this one, are available on the archive site
rtfm.mit.edu in the directory pub/usenet/news.answers.
The name under which a FAQ is archived appears in the "Archive-Name:"
line at the top of the article.  This FAQ is archived as
"unix-faq/faq/part[1-7]".

These articles are divided approximately as follows:

      1.*) General questions.
      2.*) Relatively basic questions, likely to be asked by beginners.
      3.*) Intermediate questions.
      4.*) Advanced questions, likely to be asked by people who thought
           they already knew all of the answers.
      5.*) Questions pertaining to the various shells, and the differences.
      6.*) An overview of Unix variants.
      7.*) An comparison of configuration management systems (RCS, SCCS).

This article includes answers to:

      5.1)  Can shells be classified into categories?
      5.2)  How do I "include" one shell script from within another
            shell script?
      5.3)  Do all shells have aliases?  Is there something else that
            can be used?
      5.4)  How are shell variables assigned?
      5.5)  How can I tell if I am running an interactive shell?
      5.6)  What "dot" files do the various shells use?
      5.7)  I would like to know more about the differences between the
            various shells.  Is this information available some place?

If you're looking for the answer to, say, question 5.5, and want to skip
everything else, you can search ahead for the regular expression "^5.5)".

While these are all legitimate questions, they seem to crop up in
comp.unix.questions or comp.unix.shell on an annual basis, usually
followed by plenty of replies (only some of which are correct) and then
a period of griping about how the same questions keep coming up.  You
may also like to read the monthly article "Answers to Frequently Asked
Questions" in the newsgroup "news.announce.newusers", which will tell
you what "UNIX" stands for.

With the variety of Unix systems in the world, it's hard to guarantee
that these answers will work everywhere.  Read your local manual pages
before trying anything suggested here.  If you have suggestions or
corrections for any of these answers, please send them to to
[e-mail].

----------------------------------------------------------------------

Subject: Can shells be classified into categories?
From: [e-mail] (Matthew Wicks)
Date: Wed, 7 Oct 92 14:28:18 -0500


5.1)  Can shells be classified into categories?

      In general there are two main class of shells.  The first class
      are those shells derived from the Bourne shell which includes sh,
      ksh, bash, and zsh.  The second class are those shells derived
      from C shell and include csh and tcsh.  In addition there is rc
      which most people consider to be in a "class by itself" although
      some people might argue that rc belongs in the Bourne shell class.

      With the classification above, using care, it is possible to
      write scripts that will work for all the shells from the Bourne
      shell category, and write other scripts that will work for all of
      the shells from the C shell category.

------------------------------

Subject: How do I "include" one shell script from within another shell script?
From: [e-mail] (Matthew Wicks)
Date: Wed, 7 Oct 92 14:28:18 -0500

5.2)  How do I "include" one shell script from within another shell script?

      All of the shells from the Bourne shell category (including rc)
      use the "." command.  All of the shells from the C shell category
      use "source".

------------------------------

Subject: Do all shells have aliases?  Is there something else that can be used?
From: [e-mail] (Matthew Wicks)
Date: Wed, 7 Oct 92 14:28:18 -0500

5.3)  Do all shells have aliases?  Is there something else that can be used?

      All of the major shells other than sh have aliases, but they
      don't all work the same way.  For example, some don't accept
      arguments.

      Although not strictly equivalent, shell functions (which exist in
      most shells from the Bourne shell category) have almost the same
      functionality of aliases.  Shell functions can do things that
      aliases can't do.  Shell functions did not exist in bourne shells
      derived from Version 7 Unix, which includes System III and BSD 4.2.
      BSD 4.3 and System V shells do support shell functions.

      Use unalias to remove aliases and unset to remove functions.

------------------------------

Subject: How are shell variables assigned?
From: [e-mail] (Matthew Wicks)
Date: Wed, 7 Oct 92 14:28:18 -0500

5.4)  How are shell variables assigned?

      The shells from the C shell category use "set variable=value" for
      variables local to the shell and "setenv variable value" for
      environment variables.  To get rid of variables in these shells
      use unset and unsetenv.  The shells from the Bourne shell
      category use "variable=value" and may require an "export
      VARIABLE_NAME" to place the variable into the environment.  To
      get rid of the variables use unset.

------------------------------

Subject: How can I tell if I am running an interactive shell?
From: [e-mail] (Matthew Wicks)
From: [e-mail] (DaviD W. Sanderson)
Date: Fri, 23 Oct 92 11:59:19 -0600

5.5)  How can I tell if I am running an interactive shell?

      In the C shell category, look for the variable $prompt.

      In the Bourne shell category, you can look for the variable $PS1,
      however, it is better to check the variable $-.  If $- contains
      an 'i', the shell is interactive.  Test like so:

          case $- in
          *i*)    # do things for interactive shell
                  ;;
          *)      # do things for non-interactive shell
                  ;;
          esac

------------------------------

Subject: What "dot" files do the various shells use?
From: [e-mail] (Matthew Wicks)
From: [e-mail] (Thomas M. Breuel)
Date: Wed, 28 Oct 92 03:30:36 +0100

5.6)  What "dot" files do the various shells use?

      Although this may not be a complete listing, this provides the
      majority of information.

      csh
          Some versions have system-wide .cshrc and .login files.  Every
          version puts them in different places.

          Start-up (in this order):
              .cshrc   - always.
              .login   - login shells.

          Upon termination:
              .logout  - login shells.

          Others:
              .history - saves the history (based on $savehist).

      tcsh
          Start-up (in this order):
              /etc/csh.cshrc - always.
              /etc/csh.login - login shells.
              .tcshrc        - always.
              .cshrc         - if no .tcshrc was present.
              .login         - login shells

          Upon termination:
              .logout        - login shells.

          Others:
              .history       - saves the history (based on $savehist).
              .cshdirs       - saves the directory stack.

      sh
          Start-up (in this order):
              /etc/profile - login shells.
              .profile     - login shells.

          Upon termination:
              any command (or script) specified using the command:
                 trap "command" 0

      ksh
          Start-up (in this order):
              /etc/profile - login shells.
              .profile     - login shells.
              $ENV         - always, if it is set.

          Upon termination:
              any command (or script) specified using the command:
                 trap "command" 0

      bash
          Start-up (in this order):
              /etc/profile  - login shells.
              .bash_profile - login shells.
              .profile      - login if no .bash_profile is present.
              .bashrc       - interactive non-login shells.
              $ENV          - always, if it is set.

          Upon termination:
              .bash_logout  - login shells.

          Others:
              .inputrc      - Readline initialization.

      zsh
          Start-up (in this order):
              .zshenv   - always, unless -f is specified.
              .zprofile - login shells.
              .zshrc    - interactive shells, unless -f is specified.
              .zlogin   - login shells.

          Upon termination:
              .zlogout  - login shells.

      rc
          Start-up:
              .rcrc - login shells

------------------------------

Subject: I would like to know more about the differences ... ?
From: [e-mail] (Matthew Wicks)
Date: Wed, 7 Oct 92 14:28:18 -0500

5.7)  I would like to know more about the differences between the
      various shells.  Is this information available some place?

      A very detailed comparison of sh, csh, tcsh, ksh, bash, zsh, and
      rc is available via anon.  ftp in several places:

      cs.uwp.edu (131.210.1.4):pub/vi/docs/shell-100.BetaA.Z
      utsun.s.u-tokyo.ac.jp:misc/vi-archive/docs/shell-100.BetaA.Z

      This file compares the flags, the programming syntax,
      input/output redirection, and parameters/shell environment
      variables.  It doesn't discuss what dot files are used and the
      inheritance for environment variables and functions.

------------------------------

End of unix/faq Digest part 5 of 7
**********************************

--
Ted Timar - [e-mail]
ISG Technologies Inc., 6509 Airport Road, Mississauga, Ontario, Canada L4V 1S7
Archive-name: unix-faq/faq/part6
Version: $Id: part6,v 2.5 1994/04/28 19:25:03 tmatimar Exp tmatimar $

These seven articles contain the answers to some Frequently Asked
Questions often seen in comp.unix.questions and comp.unix.shell.
Please don't ask these questions again, they've been answered plenty
of times already - and please don't flame someone just because they may
not have read this particular posting.  Thank you.

This collection of documents is Copyright (c) 1994, Ted Timar, except
Part 6, which is Copyright (c) 1994, Pierre Lewis and Ted Timar.
All rights reserved.  Permission to distribute the collection is
hereby granted providing that distribution is electronic, no money
is involved, reasonable attempts are made to use the latest version
and all credits and this copyright notice are maintained.
Other requests for distribution will be considered.  All reasonable
requests will be granted.

All information here has been contributed with good intentions, but
none of it is guaranteed either by the contributors or myself to be
accurate.  The users of this information take all responsibility for
any damage that may occur.

Many FAQs, including this one, are available on the archive site
rtfm.mit.edu in the directory pub/usenet/news.answers.
The name under which a FAQ is archived appears in the "Archive-Name:"
line at the top of the article.  This FAQ is archived as
"unix-faq/faq/part[1-7]".

These articles are divided approximately as follows:

      1.*) General questions.
      2.*) Relatively basic questions, likely to be asked by beginners.
      3.*) Intermediate questions.
      4.*) Advanced questions, likely to be asked by people who thought
           they already knew all of the answers.
      5.*) Questions pertaining to the various shells, and the differences.
      6.*) An overview of Unix variants.
      7.*) An comparison of configuration management systems (RCS, SCCS).

This article includes answers to:

      6.1)  Disclaimer, introduction and acknowledgements.
      6.2)  A very brief look at Unix history.
      6.3)  Main Unix flavors.
      6.4)  Unix Standards.
      6.5)  Identifying your Unix flavor.
      6.6)  Brief notes on some well-known (commercial/PD) Unices.
      6.7)  Real-time Unices.
      6.8)  Unix glossary.

If you're looking for the answer to, say, question 6.5, and want to skip
everything else, you can search ahead for the regular expression "^6.5)".

While these are all legitimate questions, they seem to crop up in
comp.unix.questions or comp.unix.shell on an annual basis, usually
followed by plenty of replies (only some of which are correct) and then
a period of griping about how the same questions keep coming up.  You
may also like to read the monthly article "Answers to Frequently Asked
Questions" in the newsgroup "news.announce.newusers", which will tell
you what "UNIX" stands for.

With the variety of Unix systems in the world, it's hard to guarantee
that these answers will work everywhere.  Read your local manual pages
before trying anything suggested here.  If you have suggestions or
corrections for any of these answers, please send them to to
[e-mail].

----------------------------------------------------------------------

Subject: Disclaimer, introduction and acknowledgements.
From: "Pierre (P.) Lewis" <[e-mail]>
Date: Mon May 30 15:44:28 EDT 1994
X-Version: 2.6

6.1)  Disclaimer, introduction and acknowledgements.

      The following is offered with no guarantee as to accuracy or
      completeness.  I have done what I can in the time available,
      often with conflicting information, and it still is very much work
      in progress.  I hope to keep improving this summary.  Comments and
      corrections welcome:  [e-mail].

      First a short definition.  By Unix we mean an operating system
      typically written in C, with a hierarchical file system,
      integration of file and device I/O, whose system call interface
      includes services such as fork(), pipe(), and whose user
      interface includes tools such as cc, troff, grep, awk, and a
      choice of shell.  Note that UNIX is a registered trademark of USL
      (AT&T), but will be used here in its generic sense.

      Most Unices (the more common plural form) are derived more or
      less directly from AT&T code (some code from the first C version
      is presumably still left in most), but there are also clones
      (i.e. Unix-compatible systems with no AT&T code).

      In addition, there are also Unix-like environments (e.g. VOS)
      sitting on top of other OSs, and OSs inspired from Unix (yes,
      even DOS!).  These are not covered here.  Little on real-time
      Unices yet (although more is planned).

      Unix comes in an incredible variety of flavors.  This is to a
      large extent due to availability of sources and the ease of
      porting and modifying Unix.  Typically, a vendor of Unix will
      start with one basic flavor (see below), take ideas/code from the
      other major flavor, add and change many things, etc.  This
      results in yet another new Unix flavor.  Today, there are
      literally hundreds of Unices available, the closest thing to
      standard Unix being (by definition) System V.

      This answer was put together mostly from information on the net
      and email.  Some specific sources are also mentioned in the
      appropriate sections.

      Acknowledgements: (in addition to references): [e-mail],
      [e-mail], [e-mail], [e-mail],
      [e-mail], [e-mail], [e-mail],
      [e-mail], [e-mail], [e-mail],
      [e-mail], [e-mail] [4.4BSD], [e-mail],
      [e-mail], [e-mail], [e-mail],
      [e-mail], [e-mail], [e-mail],
      [e-mail], [e-mail], [e-mail],
      [e-mail], [e-mail],
      many that I forgot, and all the other
      folks whose posts I read. Many thanks!

------------------------------

Subject: A very brief look at Unix history.
From: "Pierre (P.) Lewis" <[e-mail]>
Date: Mon May 30 15:44:28 EDT 1994
X-Version: 2.6

6.2)  A very brief look at Unix history.

      Unix history goes back to 1969 and the famous "little-used PDP-7
      in a corner" on which Ken Thompson, Dennis Ritchie (the R in K&R)
      and others started work on what was to become Unix.  The name
      "Unix" was intended as a pun on Multics (and was written "Unics"
      at first -- UNiplexed Information and Computing System).

      For the first 10 years, Unix development was essentially confined
      to Bell Labs.  These initial versions were labeled "Version n" or
      "Nth Edition" (of the manuals), and were for DEC's PDP-11 (16
      bits) and later VAXen (32 bits).  Some significant versions
      include:

      V1 (1971):  1st Unix version, in assembler on a PDP-11/20.
         Included file system, fork(), roff, ed.  Was used as a text
         processing tool for preparation of patents.  Pipe() appeared
         first in V2!

      V4 (1973):  Rewritten in C, which is probably the most
         significant event in this OS's history: it means Unix can be
         ported to a new hardware in months, and changes are easy.  The
         C language was originally designed for the Unix operating
         system, and hence there is a strong synergy between C and Unix.

      V6 (1975):  First version of Unix widely available outside
         Bell Labs (esp.  in universities).  This was also the start of
         Unix diversity and popularity.  1.xBSD (PDP-11) was derived
         from this version.  J. Lions published "A commentary on the
         Unix Operating System" based on V6.

      V7 (1979):  For many, this is the "last true Unix", an
         "improvement over all preceding and following Unices"
         [Bourne].  It included full K&R C, uucp, Bourne shell.  V7 was
         ported to the VAX as 32V.  The V7 kernel was a mere 40
         Kbytes!

         Here (for reference) are the system calls of V7:
            _exit, access, acct, alarm, brk, chdir, chmod, chown,
            chroot, close, creat, dup, dup2, exec*, exit, fork, fstat,
            ftime, getegid, geteuid, getgid, getpid, getuid, gtty,
            indir, ioctl, kill, link, lock, lseek, mknod, mount,
            mpxcall, nice, open, pause, phys, pipe, pkoff, pkon,
            profil, ptrace, read, sbrk, setgid, setuid, signal, stat,
            stime, stty, sync, tell, time, times, umask, umount,
            unlink, utime, wait, write.

      These Vn versions were developed by the Computer Research Group
      (CRG) of Bell Labs.  Another group, the Unix System Group (USG),
      was responsible for support.  A third group at Bell Labs was also
      involved in Unix development, the Programmer's WorkBench (PWB),
      to which we owe, for example, sccs, named pipes and other
      important ideas.  Both groups were merged into Unix System
      Development Lab in 1983.

      Another variant of Unix was CB Unix (Columbus Unix) from the Columbus
      branch of Bell Labs, responsible of Operations Support Systems. Its
      main contribution was parts of SV IPC.

      Work on Unix continued at Bell Labs in the 1980s.  The V series
      was further developed by the CRG (Stroustrup mentions V10 in the
      2nd edition of his book on C++), but we don't seem to hear much
      about this otherwise.  The company now responsible for Unix
      (System V) is called Unix System Laboratories (USL) and is
      majority-owned by AT&T.  Novell has bought USL (early 93)?!
      Novell has given rights to the "UNIX" trademark to X/Open (late 93).

      But much happened to Unix outside AT&T, especially at Berkeley
      (where the other major flavor comes from).  Vendors (esp. of
      workstations) also contributed much (e.g. Sun's NFS).

      The book "Life with Unix" by Don Libes and Sandy Ressler is
      fascinating reading for anyone interested in Unix, and covers a
      lot of the history, interactions, etc..  Much in the present
      section is summarized from this book.

------------------------------

Subject: Main Unix flavors.
From: "Pierre (P.) Lewis" <[e-mail]>
Date: Mon May 30 15:44:28 EDT 1994
X-Version: 2.7

6.3)  Main Unix flavors.

      Until recently, there were basically two main flavors of Unix:
      System V (five) from AT&T, and the Berkeley Software Distribution
      (BSD).  SVR4 is essentially a merge of these two flavors.  End
      '91, OSF/1 from the Open Software Foundation was released (as a
      direct competitor to System V) and may (future will tell) change
      this picture.

      The following lists the main releases and features of System V,
      BSD and OSF/1.

      System V from AT&T.  Typical of Intel hardware.  Most often
         ported Unix, typically with BSD enhancements (csh, job
         control, termcap, curses, vi, symbolic links).  System V
         evolution is now overseen by Unix International (UI).  UI
         members include AT&T, Sun, ....
         Newsgroup: comp.unix.sysv[23]86.  Main releases:

         - System III (1982): first commercial Unix from AT&T
           - FIFOs (named pipes)  (later?)

         - System V (1983):
           - IPC package (shm, msg, sem)

         - SVR2 (1984):
           - shell functions (sh)
           - SVID (System V Interface Definition)

         - SVR3 (1986) for ? platforms:
           - STREAMS (inspired by V8), poll(), TLI (network software)
           - RFS
           - shared libs
           - SVID 2
           - demand paging (if hardware supports)

         - SVR3.2:
           - merge with Xenix (Intel 80386)
           - networking

         - SVR4 (1988), mainstream of Unix implementations, merge of
           System V, BSD, and SunOS.
           - From SVR3: sysadmin, terminal I/F, printer (from BSD?),
             RFS, STREAMS, uucp
           - From BSD: FFS, TCP/IP, sockets, select(), csh
           - From SunOS: NFS, OpenLook GUI, X11/NeWS, virtual memory
             subsystem with memory-mapped files, shared libraries
             (!= SVR3 ones?)
           - ksh
           - ANSI C
           - Internationalization (8-bit clean)
           - ABI (Application Binary Interface -- routines instead of traps)
           - POSIX, X/Open, SVID3

         - SVR4.1
           - async I/O (from SunOS?)

         - SVR4.2 (based on SVR4.1ES)
           - Veritas FS, ACLs
           - Dynamically loadable kernel modules

         - Future:
           - SVR4 MP (multiprocessor)
           - Use of Chorus microkernel?

      Berkeley Software Distribution (BSD).  Typical of VAXen, RISCs,
         many workstations.  More dynamic, research versions now than
         System V.  BSD is responsible for much of the popularity of
         Unix.  Most enhancements to Unix started here.  The group
         responsible at UCB (University of California at Berkeley) is
         the Computer System Research Group (CSRG).  They closed down
         in 1992.  Newsgroup: comp.unix.bsd.  Main releases:

         (much reorganized wrt dates and releases, hope it's converging)

         - 2.xBSD (1978) for PDP-11, still of significance? (2.11BSD
           was released in 1992!).
           - csh

         - 3BSD (1978):
           - virtual memory

         - 4.?BSD:
           - termcap, curses
           - vi

         - 4.0BSD (1980):

         - 4.1BSD (?): base of later AT&T CRG versions
           - job control
           - automatic kernel config
           - vfork()

         - 4.2BSD (1983):
           - TCP/IP, sockets, ethernet
           - UFS: long file names, symbolic links
           - new reliable signals (4.1 reliable signals now in SVR3)
           - select()

         - 4.3BSD (1986) for VAX, ?:
         - 4.3 Tahoe (1988): 4.3BSD with sources, support for Tahoe
           (32-bit supermini)
           - Fat FFS
           - New TCP algorithms
         - 4.3 Reno (1990) for VAX, Tahoe, HP 9000/300:
           - most of P1003.1
           - NFS (from Sun)
           - MFS (memory file system)
           - OSI: TP4, CLNP, ISODE's FTAM, VT and X.500;  SLIP
           - Kerberos

         - Net1 (?) and Net2 (June 1991) tapes: that portion of BSD which
           requires no USL copyright

         - 4.4BSD (alpha June 1992) for HP 9000/300, Sparc, 386, DEC, others;
           neither VAX nor Tahoe; two versions, lite (~Net2 contents plus,
           fixes and new architectures) and encumbered (everything, requires
           USL license):
           - new virtual memory system (VMS) based on Mach 2.5
           - virtual filesystem interface, log-structured filesystem, size
             of local filesystem up to 2^63, NFS (freely redistributable,
             works with Sun's, over UDP or TCP)
           - ISO/OSI networking support (based on ISODE): TP4/CLNP/802.3 and
             TP0/CONS/X.25, session and above in user space;  FTAM, VT, X.500.
           - most of POSIX.1 (esp. new terminal driver a la SV), much of
             POSIX.2, improved job control; ANSI C headers
           - Kerberos integrated with much of the system (incl. NFS)
           - TCP/IP enhancements (incl. header prediction, SLIP)
           - important kernel changes (new system call convention, ...)
           - other improvements: FIFOs, byte-range file locking
           Official 4.4BSD release was expected within 6 months of above.

      The Open Software Foundation (OSF) released its Unix called OSF/1
         end of 1991.  Still requires an SVR2 license.
         Compatible/compliant with SVID 2 (and 3 coming), POSIX,
         X/Open, etc..  OSF members include Apollo, Dec, HP, IBM, ....

         - OSF/1 (1991):
           - based on Mach 2.5 kernel
           - symmetric multiprocessing, parallelized kernel, threads
           - logical volumes, disk mirroring, UFS (native), S5 FS, NFS
           - enhanced security (B1 with some B2, B3; or C2), 4.3BSD admin
           - STREAMS, TLI/XTI, sockets
           - shared libs, dynamic loader (incl. kernel)
           - Motif GUI

         - Release 1.3 (Jun 94)
           - Based on MACH 3.0 Micro-kernel
           - Conformant with current draft of Specification 1170
             (considered for standardization in X/Open's Fast Track process)
           - Data Capture I/F, Common Data Link I/F,
           - ISO 10646 and 64-bit support.
           - OSF/1 MK (mikrokernel) based on Mach 3.0

      This list of major flavors should probably also include Xenix
      (Microsoft) which has been the basis for many ports.  Derived from V7,
      S III and finally System V, it is similar externally but significantly
      changed internally (performance-tuned for micros).


      Two very good books describe the internals of the two main flavors.
      These are:
      - System V: "Design of the Unix Operating SYstem", M.J. Bach.
      - BSD: "Design and Implementation of the 4.3BSD Unix Operating System",
        Leffler, McKusick, Karels, Quaterman.
      For a good introduction to OSF/1 (not quite as technical as the
      previous two), see: "Guide to OSF/1, A Technical Synopsis",
      published by O'Reilly.  On SunOS, "Virtual Memory Architecture in
      SunOS" and "Shared Libraries in SunOS" in Summer 1989 USENIX
      Proceedings.

      A good set of articles on where Unix is going is "Unix Variants"
      in the Apr 92 issue of Unix Review.  Other good sources of
      information include the bsd-faq file, and many of the newsgroups
      mentioned in the text.

------------------------------

Subject: Unix Standards.
From: "Pierre (P.) Lewis" <[e-mail]>
Date: Mon May 30 15:44:28 EDT 1994
X-Version: 2.6

6.4)  Unix Standards.

      This section briefly describes the more important standards
      relevant to Unix.

      - IEEE:
        - 802.x (LAN) standards (LLC, ethernet, token ring, token bus)
        - POSIX (ISO 9945?): Portable Operating System I/F (Unix, VMS
          and OS/2!) (only ? have been finalized at this point)
          - 1003.1:  library procedures (mostly system calls) -- roughly V7
                     except for signals and terminal I/F (1990)
          - 1003.2:  shell and utilities
          - 1003.3:  test methods and conformance
          - 1003.4:  real-time: binary semaphores, process memory
                     locking, memory-mapped files, shared memory,
                     priority scheduling, real-time signals, clocks and
                     timers, IPC message passing, synchronized I/O,
                     asynchronous I/O, real-time files
          - 1003.5:  Ada language bindings
          - 1003.6:  security
          - 1003.7:  system admin (incl. printing)
          - 1003.8:  transparent file access
          - 1003.9:  FORTRAN language bindings
          - 1003.10: super computing
          - 1003.12: protocol-independent I/Fs
          - 1003.13: real-time profiles
          - 1003.15: supercomputing batch I/Fs
          - 1003.16: C-language bindings (?)
          - 1003.17: directory services
          - 1003.18: POSIX standardized profile
          - 1003.19: FORTRAN 90 language bindings

      - X/Open (consortium of vendors, founded 1984):
        - X/Open Portability Guides (XPGn):
          - XPG2 (1987), strong SV influence
            Vol 1:  commands and utilities
            Vol 2:  system calls and libraries
            Vol 3:  terminal I/F (curses, termio), IPC (SV),
                    internationalization
            Vol 4:  programming languages (C, COBOL!)
            Vol 5:  data management (ISAM, SQL)
          - XPG3 (1989) adds: X11 API
          - XPG4 (1992) adds: XTI?   22 components
        - XOM series of interfaces:
          - XOM (X/Open Object Management) generic I/F mechanisms for
            following
          - XDS (X/Open Directory Service)
          - XMH (X/Open Mail ??)
          - XMP (X/Open Management Protocols) -- not Bull's CM API?
        - X/Open now has the rights to the "UNIX" trademark (late 93);
        - "Spec 1170"
          - This specification is being prepared describing a common API
            which vendors wanting to use the name "UNIX" will have to comply
            to (when test suites are available). Merge of SVID, OSF's AES
            and other stuff.

      - AT&T
        - System V Interface Definition (SVID)
          - SVID1 (1985, SVR2)
            Vol 1:  system calls and libraries (similar to XPG2.1)
          - SVID2 (1986, SVR3)
            Vol 1:  system calls and libraries (base, kernel extensions)
            Vol 2:  commands and utilities (base, advanced, admin, software
                    development), terminal I/F
            Vol 3:  terminal I/F (again), STREAMS and TLI, RFS
          - SVID3 (19??, SVR4) adds
            Vol 4:  ??  &c
        - APIs
          - Transport Library Interface (TLI)
          - ACSE/Presentation Library Interface (APLI)

------------------------------

Subject: Identifying your Unix flavor.
From: "Pierre (P.) Lewis" <[e-mail]>
Date: Mon May 30 15:44:28 EDT 1994
X-Version: 2.6

6.5)  Identifying your Unix flavor.

      This section lists a number of things you can look at in
      attempting to identify the base flavor of your Unix.  Given the
      significant exchange of code and ideas between the various
      flavors and the many changes made by vendors, any statement such
      as "this Unix is an SVR2" is at best a statistical statement
      (except for some SVRn ports).  Also many Unices offer most of
      both worlds (either mixed as in SunOS or strictly separated as in
      Apollo?).  So this section is perhaps not very useful...

      The list of features in previous sections can also help.  For
      example, if a system has a poll(2) but no select(2), it is highly
      probable that it is derived from SVR3.  Also the name of the OS
      can provide a clue, as well as the logon message (e.g.  SGI's
      "IRIX SVR3.3.2") or the output of "uname -a" command.  Available
      commands can also provide hints but this is probably less
      reliable than kernel features.  For example, the type of terminal
      initialization (inittab or ttys) is a more reliable indicator
      than the print subsystem.

      Feature           Typical in SVRx         Typical in xBSD

      kernel name       /unix                   /vmunix
      terminal init     /etc/inittab            /etc/ttys (only getty to 4.3)
      boot init         /etc/rc.d directories   /etc/rc.* files
      mounted FSs       /etc/mnttab             /etc/mtab
      usual shell       sh, ksh                 csh, #! hack
      native FS         S5 (blk: 512-2K)        UFS (blk: 4K-8K)
                        file names <= 14 bytes  file names < 255 bytes
      groups            need newgrp(1)          automatic membership
                        SVR4: multiple groups
      print subsystem   lp, lpstat, cancel      lpr, lpq, lprm (lpd daemon) ??
      terminal control  termio, terminfo,       termios (sgtty before 4.3reno)
                        SVR4: termios (POSIX)   termcap
      job control       >= SVR4                 yes
      ps command        ps -ef                  ps -aux
      multiple wait     poll                    select
      string fcns       memset, memcpy          bzero, bcopy
      process mapping   /proc  (SVR4)

------------------------------

Subject: Brief notes on some well-known (commercial/PD) Unices.
From: "Pierre (P.) Lewis" <[e-mail]>
Date: Mon May 30 15:44:28 EDT 1994
X-Version: 2.6

6.6)  Brief notes on some well-known (commercial/PD) Unices.

      (I am not at all satisfied with this section, unfortunately I
      have neither the time nor the documents to make it much better
      (wrt contents).  Should only list Unices known by a reasonably
      wide audience.  Small and non-US Unices welcome, e.g. Eurix.  In
      need of reformatting)

      This section lists (in alphabetical order) some of the better
      known Unices along with a brief description of their nature.
      Unfortunately, it's out-of-date almost by definition...

      (sorted alpha, ignoring numbers and other chars)

      AIX:  IBM's Unix, based on SVR2 (later up to SVR3.2?) with varying
         degrees of BSD extensions, for various hardwares.  Proprietary
         system admin (SMIT).  Both 850 and Latin-1 CPs.  Quite
         different from most Unices and among themselves.
         Newsgroup: comp.unix.aix.
         - 1.x (for 386 PS/2)
         - 2.x (for PC RTs)
         - 3.x (for RS/6000), paging kernel, logical volume manager, i18n;
           3.2 adds TLI/STREAMS.  SV-based with many enhancements.
         - AIX/ESA, runs native on S/370 and S/390 mainframes, based on OSF/1.
         AIX was to have been base for OSF/1 until Mach was chosen instead.
         I hope this subsection is converging :-)

      AOS (IBM):  4.3BSD port to IBM PC RT (for educational institutes).
         Don't confuse with DG's proprietary OS of same name.

      Arix:  SV

      A/UX (Apple): SV with Berkeley enhancements, NFS, Mac GUI.  System 6
         (later System 7) runs as guest of A/UX (opposite of MachTen).
         Newsgroup: comp.unix.aux.
         - 2.0:  SVR2 with 4.2BSD, system 6 Mac applications.
         - 3.0 (1992): SVR2.2 with 4.3BSD and SVR3/4 extensions; X11R4,
           MacX, TCP/IP, NFS, NIS, RPC/XDR, various shells, UFS or S5FS.
           System 7 applications.
         - 4.0 will have/be OSF/1.

      3B1 (680x0): SV-based, done by Convergent for AT&T.
         Newsgroup: comp.sys.3b1.

      BNR/2: stands for BSD Net/2 Release? Includes NetBSD/1, FreeBSD.

      BOS for Bull's DPX/2 (680x0)
         - V1 (1990): SVR3 with BSD extensions (FFS, select, sockets),
           symmetric MP, X11R3
         - V2 (1 death and continues to
      work), and the grandchild does whatever the child was originally
      supposed to.  Since its parent died, it is inherited by init,
      which will do whatever waiting is needed.  This method is
      inefficient because it requires an extra fork, but is pretty much
      completely portable.

------------------------------

Subject: How do I get lines from a pipe ... instead of only in larger blocks?
From: [e-mail] (Jonathan I. Kamens)
Date: Sun, 16 Feb 92 20:59:28 -0500

3.14) How do I get lines from a pipe as they are written instead of only in
      larger blocks?

      The stdio library does buffering differently depending on whether
      it thinks it's running on a tty.  If it thinks it's on a tty, it
      does buffering on a per-line basis; if not, it uses a larger
      buffer than one line.

      If you have the source code to the client whose buffering you
      want to disable, you can use setbuf() or setvbuf() to change the
      buffering.

      If not, the best you can do is try to convince the program that
      it's running on a tty by running it under a pty, e.g. by using
      the "pty" program mentioned in question 3.9.

------------------------------

End of unix/faq Digest part 3 of 7
**********************************

--
Ted Timar - [e-mail]
ISG Technologies Inc., 6509 Airport Road, Mississauga, Ontario, Canada L4V 1S7
Archive-name: unix-faq/faq/part4
Version: $Id: part4,v 2.5 1994/04/28 19:25:03 tmatimar Exp tmatimar $

These seven articles contain the answers to some Frequently Asked
Questions often seen in comp.unix.questions and comp.unix.shell.
Please don't ask these questions again, they've been answered plenty
of times already - and please don't flame someone just because they may
not have read this particular posting.  Thank you.

This collection of documents is Copyright (c) 1994, Ted Timar, except
Part 6, which is Copyright (c) 1994, Pierre Lewis and Ted Timar.
All rights reserved.  Permission to distribute the collection is
hereby granted providing that distribution is electronic, no money
is involved, reasonable attempts are made to use the latest version
and all credits and this copyright notice are maintained.
Other requests for distribution will be considered.  All reasonable
requests will be granted.

All information here has been contributed with good intentions, but
none of it is guaranteed either by the contributors or myself to be
accurate.  The users of this information take all responsibility for
any damage that may occur.

Many FAQs, including this one, are available on the archive site
rtfm.mit.edu in the directory pub/usenet/news.answers.
The name under which a FAQ is archived appears in the "Archive-Name:"
line at the top of the article.  This FAQ is archived as
"unix-faq/faq/part[1-7]".

These articles are divided approximately as follows:

      1.*) General questions.
      2.*) Relatively basic questions, likely to be asked by beginners.
      3.*) Intermediate questions.
      4.*) Advanced questions, likely to be asked by people who thought
           they already knew all of the answers.
      5.*) Questions pertaining to the various shells, and the differences.
      6.*) An overview of Unix variants.
      7.*) An comparison of configuration management systems (RCS, SCCS).

This article includes answers to:

      4.1)  How do I read characters from a terminal without requiring the user
              to hit RETURN?
      4.2)  How do I check to see if there are characters to be read without
              actually reading?
      4.3)  How do I find the name of an open file?
      4.4)  How can an executing program determine its own pathname?
      4.5)  How do I use popen() to open a process for reading AND writing?
      4.6)  How do I sleep() in a C program for less than one second?
      4.7)  How can I get setuid shell scripts to work?
      4.8)  How can I find out which user or process has a file open or is using
            a particular file system (so that I can unmount it?)
      4.9)  How do I keep track of people who are fingering me?
      4.10) Is it possible to reconnect a process to a terminal after it has
            been disconnected, e.g. after starting a program in the background
            and logging out?
      4.11) Is it possible to "spy" on a terminal, displaying the output
            that's appearing on it on another terminal?

If you're looking for the answer to, say, question 4.5, and want to skip
everything else, you can search ahead for the regular expression "^4.5)".

While these are all legitimate questions, they seem to crop up in
comp.unix.questions or comp.unix.shell on an annual basis, usually
followed by plenty of replies (only some of which are correct) and then
a period of griping about how the same questions keep coming up.  You
may also like to read the monthly article "Answers to Frequently Asked
Questions" in the newsgroup "news.announce.newusers", which will tell
you what "UNIX" stands for.

With the variety of Unix systems in the world, it's hard to guarantee
that these answers will work everywhere.  Read your local manual pages
before trying anything suggested here.  If you have suggestions or
corrections for any of these answers, please send them to to
[e-mail].

----------------------------------------------------------------------

Subject: How do I read characters ... without requiring the user to hit RETURN?
Date: Thu Mar 18 17:16:55 EST 1993

4.1)  How do I read characters from a terminal without requiring the user
      to hit RETURN?

      Check out cbreak mode in BSD, ~ICANON mode in SysV.

      If you don't want to tackle setting the terminal parameters
      yourself (using the "ioctl(2)" system call) you can let the stty
      program do the work - but this is slow and inefficient, and you
      should change the code to do it right some time:

      #include <stdio.h>
      main()
      {
            int c;

            printf("Hit any character to continue\n");
            /*
             * ioctl() would be better here; only lazy
             * programmers do it this way:
             */
            system("/bin/stty cbreak");        /* or "stty raw" */
            c = getchar();
            system("/bin/stty -cbreak");
            printf("Thank you for typing %c.\n", c);

            exit(0);
      }

      Several people have sent me various more correct solutions to
      this problem.  I'm sorry that I'm not including any of them here,
      because they really are beyond the scope of this list.

      You might like to check out the documentation for the "curses"
      library of portable screen functions.  Often if you're interested
      in single-character I/O like this, you're also interested in
      doing some sort of screen display control, and the curses library
      provides various portable routines for both functions.

------------------------------

Subject: How do I check to see if there are characters to be read ... ?
Date: Thu Mar 18 17:16:55 EST 1993

4.2)  How do I check to see if there are characters to be read without
      actually reading?

      Certain versions of UNIX provide ways to check whether characters
      are currently available to be read from a file descriptor.  In
      BSD, you can use select(2).  You can also use the FIONREAD ioctl
      (see tty(4)), which returns the number of characters waiting to
      be read, but only works on terminals, pipes and sockets.  In
      System V Release 3, you can use poll(2), but that only works on
      streams.  In Xenix - and therefore Unix SysV r3.2 and later - the
      rdchk() system call reports whether a read() call on a given file
      descriptor will block.

      There is no way to check whether characters are available to be
      read from a FILE pointer.  (You could poke around inside stdio
      data structures to see if the input buffer is nonempty, but that
      wouldn't work since you'd have no way of knowing what will happen
      the next time you try to fill the buffer.)

      Sometimes people ask this question with the intention of writing
            if (characters available from fd)
                    read(fd, buf, sizeof buf);
      in order to get the effect of a nonblocking read.  This is not
      the best way to do this, because it is possible that characters
      will be available when you test for availability, but will no
      longer be available when you call read.  Instead, set the
      O_NDELAY flag (which is also called FNDELAY under BSD) using the
      F_SETFL option of fcntl(2).  Older systems (Version 7, 4.1 BSD)
      don't have O_NDELAY; on these systems the closest you can get to
      a nonblocking read is to use alarm(2) to time out the read.

------------------------------

Subject: How do I find the name of an open file?
Date: Thu Mar 18 17:16:55 EST 1993

4.3)  How do I find the name of an open file?

      In general, this is too difficult.  The file descriptor may
      be attached to a pipe or pty, in which case it has no name.
      It may be attached to a file that has been removed.  It may
      have multiple names, due to either hard or symbolic links.

      If you really need to do this, and be sure you think long
      and hard about it and have decided that you have no choice,
      you can use find with the -inum and possibly -xdev option,
      or you can use ncheck, or you can recreate the functionality
      of one of these within your program.  Just realize that
      searching a 600 megabyte filesystem for a file that may not
      even exist is going to take some time.

------------------------------

Subject: How can an executing program determine its own pathname?
Date: Thu Mar 18 17:16:55 EST 1993

4.4)  How can an executing program determine its own pathname?

      Your program can look at argv[0]; if it begins with a "/", it is
      probably the absolute pathname to your program, otherwise your
      program can look at every directory named in the environment
      variable PATH and try to find the first one that contains an
      executable file whose name matches your program's argv[0] (which
      by convention is the name of the file being executed).  By
      concatenating that directory and the value of argv[0] you'd
      probably have the right name.

      You can't really be sure though, since it is quite legal for one
      program to exec() another with any value of argv[0] it desires.
      It is merely a convention that new programs are exec'd with the
      executable file name in argv[0].

      For instance, purely a hypothetical example:

        #include <stdio.h>
        main()
        {
            execl("/usr/games/rogue", "vi Thesis", (char *)NULL);
        }

      The executed program thinks its name (its argv[0] value) is
      "vi Thesis".   (Certain other programs might also think that
      the name of the program you're currently running is "vi Thesis",
      but of course this is just a hypothetical example, don't
      try it yourself :-)

------------------------------

Subject: How do I use popen() to open a process for reading AND writing?
Date: Thu Mar 18 17:16:55 EST 1993

4.5)  How do I use popen() to open a process for reading AND writing?

      The problem with trying to pipe both input and output to an
      arbitrary slave process is that deadlock can occur, if both
      processes are waiting for not-yet-generated input at the same
      time.  Deadlock can be avoided only by having BOTH sides follow a
      strict deadlock-free protocol, but since that requires
      cooperation from the processes it is inappropriate for a
      popen()-like library function.

      The 'expect' distribution includes a library of functions that a
      C programmer can call directly.  One of the functions does the
      equivalent of a popen for both reading and writing.  It uses ptys
      rather than pipes, and has no deadlock problem.  It's portable to
      both BSD and SV.  See the next answer for more about 'expect'.

------------------------------

Subject: How do I sleep() in a C program for less than one second?
Date: Thu Mar 18 17:16:55 EST 1993

4.6)  How do I sleep() in a C program for less than one second?

      The first thing you need to be aware of is that all you can
      specify is a MINIMUM amount of delay; the actual delay will
      depend on scheduling issues such as system load, and could be
      arbitrarily large if you're unlucky.

      There is no standard library function that you can count on in
      all environments for "napping" (the usual name for short
      sleeps).  Some environments supply a "usleep(n)" function which
      suspends execution for n microseconds.  If your environment
      doesn't support usleep(), here are a couple of implementations
      for BSD and System V environments.

      The following code is adapted from Doug Gwyn's System V emulation
      support for 4BSD and exploits the 4BSD select() system call.
      Doug originally called it 'nap()'; you probably want to call it
      "usleep()";

      /*
            usleep -- support routine for 4.2BSD system call emulations
            last edit:  29-Oct-1984     D A Gwyn
      */

      extern int        select();

      int
      usleep( usec )                            /* returns 0 if ok, else -1 */
            long                usec;           /* delay in microseconds */
            {
            static struct                       /* `timeval' */
                    {
                    long        tv_sec;         /* seconds */
                    long        tv_usec;        /* microsecs */
                    }   delay;          /* _select() timeout */

            delay.tv_sec = usec / 1000000L;
            delay.tv_usec = usec % 1000000L;

            return select( 0, (long *)0, (long *)0, (long *)0, &delay );
            }

      On System V you might do it this way:

      /*
      subseconds sleeps for System V - or anything that has poll()
      Don Libes, 4/1/1991

      The BSD analog to this function is defined in terms of
      microseconds while poll() is defined in terms of milliseconds.
      For compatibility, this function provides accuracy "over the long
      run" by truncating actual requests to milliseconds and
      accumulating microseconds across calls with the idea that you are
      probably calling it in a tight loop, and that over the long run,
      the error will even out.

      If you aren't calling it in a tight loop, then you almost
      certainly aren't making microsecond-resolution requests anyway,
      in which case you don't care about microseconds.  And if you did,
      you wouldn't be using UNIX anyway because random system
      indigestion (i.e., scheduling) can make mincemeat out of any
      timing code.

      Returns 0 if successful timeout, -1 if unsuccessful.

      */

      #include <poll.h>

      int
      usleep(usec)
      unsigned int usec;                /* microseconds */
      {
            static subtotal = 0;        /* microseconds */
            int msec;                   /* milliseconds */

            /* 'foo' is only here because some versions of 5.3 have
             * a bug where the first argument to poll() is checked
             * for a valid memory address even if the second argument is 0.
             */
            struct pollfd foo;

            subtotal += usec;
            /* if less then 1 msec request, do nothing but remember it */
            if (subtotal < 1000) return(0);
            msec = subtotal/1000;
            subtotal = subtotal%1000;
            return poll(&foo,(unsigned long)0,msec);
      }

      Another possibility for nap()ing on System V, and probably other
      non-BSD Unices is Jon Zeeff's s5nap package, posted to
      comp.sources.misc, volume 4.  It does require a installing a
      device driver, but works flawlessly once installed.  (Its
      resolution is limited to the kernel HZ value, since it uses the
      kernel delay() routine.)

------------------------------

Subject: How can I get setuid shell scripts to work?
Date: Thu Mar 18 17:16:55 EST 1993

4.7)  How can I get setuid shell scripts to work?

      [ This is a long answer, but it's a complicated and frequently-asked
        question.  Thanks to Maarten Litmaath for this answer, and
        for the "indir" program mentioned below. ]

      Let us first assume you are on a UNIX variant (e.g. 4.3BSD or
      SunOS) that knows about so-called `executable shell scripts'.
      Such a script must start with a line like:

        #!/bin/sh

      The script is called `executable' because just like a real (binary)
      executable it starts with a so-called `magic number' indicating
      the type of the executable.  In our case this number is `#!' and
      the OS takes the rest of the first line as the interpreter for
      the script, possibly followed by 1 initial option like:

        #!/bin/sed -f

      Suppose this script is called `foo' and is found in /bin,
      then if you type:

        foo arg1 arg2 arg3

      the OS will rearrange things as though you had typed:

        /bin/sed -f /bin/foo arg1 arg2 arg3

      There is one difference though: if the setuid permission bit for
      `foo' is set, it will be honored in the first form of the
      command; if you really type the second form, the OS will honor
      the permission bits of /bin/sed, which is not setuid, of course.

      ----------

      OK, but what if my shell script does NOT start with such a `#!'
      line or my OS does not know about it?

      Well, if the shell (or anybody else) tries to execute it, the OS
      will return an error indication, as the file does not start with
      a valid magic number.  Upon receiving this indication the shell
      ASSUMES the file to be a shell script and gives it another try:

        /bin/sh shell_script arguments

      But we have already seen that a setuid bit on `shell_script' will
      NOT be honored in this case!

      ----------

      Right, but what about the security risks of setuid shell scripts?

      Well, suppose the script is called `/etc/setuid_script', starting
      with:

        #!/bin/sh

      Now let us see what happens if we issue the following commands:

        $ cd /tmp
        $ ln /etc/setuid_script -i
        $ PATH=.
        $ -i

      We know the last command will be rearranged to:

        /bin/sh -i

      But this command will give us an interactive shell, setuid to the
      owner of the script!
      Fortunately this security hole can easily be closed by making the
      first line:

        #!/bin/sh -

      The `-' signals the end of the option list: the next argument `-i'
      will be taken as the name of the file to read commands from, just
      like it should!

      ---------

      There are more serious problems though:

        $ cd /tmp
        $ ln /etc/setuid_script temp
        $ nice -20 temp &
        $ mv my_script temp

      The third command will be rearranged to:

        nice -20 /bin/sh - temp

      As this command runs so slowly, the fourth command might be able
      to replace the original `temp' with `my_script' BEFORE `temp' is
      opened by the shell!  There are 4 ways to fix this security hole:

        1)  let the OS start setuid scripts in a different, secure way
            - System V R4 and 4.4BSD use the /dev/fd driver to pass the
            interpreter a file descriptor for the script

        2)  let the script be interpreted indirectly, through a frontend
            that makes sure everything is all right before starting the
            real interpreter - if you use the `indir' program from
            comp.sources.unix the setuid script will look like this:

                #!/bin/indir -u
                #?/bin/sh /etc/setuid_script

        3)  make a `binary wrapper': a real executable that is setuid and
            whose only task is to execute the interpreter with the name of
            the script as an argument

        4)  make a general `setuid script server' that tries to locate the
            requested `service' in a database of valid scripts and upon
            success will start the right interpreter with the right
            arguments.

      ---------

      Now that we have made sure the right file gets interpreted, are
      there any risks left?

      Certainly!  For shell scripts you must not forget to set the PATH
      variable to a safe path explicitly.  Can you figure out why?
      Also there is the IFS variable that might cause trouble if not
      set properly.  Other environment variables might turn out to
      compromise security as well, e.g. SHELL...  Furthermore you must
      make sure the commands in the script do not allow interactive
      shell escapes!  Then there is the umask which may have been set
      to something strange...

      Etcetera.  You should realise that a setuid script `inherits' all
      the bugs and security risks of the commands that it calls!

      All in all we get the impression setuid shell scripts are quite a
      risky business!  You may be better off writing a C program instead!

------------------------------

Subject: How can I find out which user or process has a file open ... ?
Date: Thu Mar 18 17:16:55 EST 1993

4.8)  How can I find out which user or process has a file open or is using
      a particular file system (so that I can unmount it?)

      Use fuser (system V), fstat (BSD), ofiles (public domain) or
      pff (public domain).  These programs will tell you various things
      about processes using particular files.

      A port of the 4.3 BSD fstat to Dynix, SunOS and Ultrix
      can be found in archives of comp.sources.unix, volume 18.

      pff is part of the kstuff package, and works on quite a few systems.
      Instructions for obtaining kstuff are provided in question 3.10.

------------------------------

Subject: How do I keep track of people who are fingering me?
From: [e-mail] (Jonathan I. Kamens)
From: [e-mail] (Nikola Malenovic)
Date: Mon, 23 Nov 1992 16:01:45 -0600

4.9)  How do I keep track of people who are fingering me?

      Generally, you can't find out the userid of someone who is
      fingering you from a remote machine.  You may be able to
      find out which machine the remote request is coming from.
      One possibility, if your system supports it and assuming
      the finger daemon doesn't object, is to make your .plan file a
      "named pipe" instead of a plain file.  (Use 'mknod' to do this.)

      You can then start up a program that will open your .plan file
      for writing; the open will block until some other process (namely
      fingerd) opens the .plan for reading.  Now you can whatever you
      want through this pipe, which lets you show different .plan
      information every time someone fingers you.

      Of course, this may not work at all if your system doesn't
      support named pipes or if your local fingerd insists
      on having plain .plan files.

      Your program can also take the opportunity to look at the output
      of "netstat" and spot where an incoming finger connection is
      coming from, but this won't get you the remote user.

      Getting the remote userid would require that the remote site be
      running an identity service such as RFC 931.  There are now three
      RFC 931 implementations for popular BSD machines, and several
      applications (such as the wuarchive ftpd) supporting the server.
      For more information join the rfc931-users mailing list,
      [e-mail].

      There are three caveats relating to this answer.  The first is
      that many NFS systems won't recognize the named pipe correctly.
      This means that trying to read the pipe on another machine will
      either block until it times out, or see it as a zero-length file,
      and never print it.

      The second problem is that on many systems, fingerd checks that
      the .plan file contains data (and is readable) before trying to
      read it.  This will cause remote fingers to miss your .plan file
      entirely.

      The third problem is that a system that supports named pipes
      usually has a fixed number of named pipes available on the
      system at any given time - check the kernel config file and
    com>

7.13) RCS vs SCCS:  Acknowledgements

      I would like to thank the following persons for contributing to
      these articles.  I'd like to add your name to the list--please
      send comments or more references to Bill Wohler <[e-mail]>.

        Karl Vogel <[e-mail]>
        Mark Runyan <[e-mail]>
        Paul Eggert <[e-mail]>
        Greg Henderson <[e-mail]>
        Dave Goldberg <[e-mail]>
        Rob Kurver <[e-mail]>
        Raymond Chen <[e-mail]>
        Dwight <[e-mail]>

------------------------------

Subject: Can I get more information on configuration management systems?
Date: Thu Oct 15 10:27:47 EDT 1992
From: Ted Timar <[e-mail]>

7.14) Can I get more information on configuration management systems?

      Bill Wohler, who compiled all of the information in this part of
      the FAQ, has compiled much more information.  This information is
      available for ftp from ftp.wg.omron.co.jp (133.210.4.4) under
      "pub/unix-faq/docs/rev-ctl-sys".

------------------------------

End of unix/faq Digest part 7 of 7
**********************************

--
Ted Timar - [e-mail]
ISG Technologies Inc., 6509 Airport Road, Mississauga, Ontario, Canada L4V 1S7