Garbo/Garbo.cdr/pc/unix/csh4.arc/SHELL.DOC

Text File | 1985-09-05 | 15.2 KB | 462 lines

        shell.exe


        command processor for ms.dos


        This is  yet  another  command.com  replacement.    It implements
        unix-like shell commands (ls, mv, fgrep, rm, chdir,  chmod)  etc.
        Other features include:


        1. Command line expansion of ambiguous file names.


        Programs  invoked  from  shell   never see '*.*' as an argument -
        they see  the  list  of  all  matching  files  in    the  current
        directory.


        2. History substitution - ala C-shell.


        History substitution is a powerful means to save retyping of long
        command lines.It allows you to do things like re-execute the last
        command,  re-execute  the  last  command but redirect output to a
        file, or execute a  new  command  with  arguments  from  previous
        command  lines.    The  last  20  commands  are saved, and can be
        reviewed by typing the 'history' command.


        Previous commands can be referred to by their number, or relative
        to the  current  command's  number.    Parameters  from  previous
        commands can be seperated out and used individually.


        History  substitutions  specifications  come  in  two parts - the
        command number  specifier and the argument  specifier,  seperated
        by a  colon.    The  argument    specifier  is optional; if it is
        omitted, the entire command line is specified.


            <command specifier> ::= !! | !n | !-n
            !!  = last command
            !n  = nth command
            !-n = command n commands before current command number


            <argument specifier> ::= :[^$*] | :n | :n* | <empty>
            n   = number of argument (0 being the command name)
            ^   = first argument (i.e. argv[1])
            $   = last argument
            *   = ^-$, or nothing if only one word on command line
            n*  = arguments n through $


            <history subst specification> ::= <command specifier><argument specifier>


        This is not as complicatated as  it  may  appear.    Here  is  an
        example session.


            0% ls *.c
            *.c
            foo.c bar.c
            1% more foo.c
            /* edit the last argument of the last command */
            2% edit !!:$
            /* go off and edit */
            /* reference last argument of last command */
            3% fgrep foo !!:$ bar.c
            FOO.C : foo
            BAR.C : foo
            /* edit the second thru the last args of command 3 */









            4% edit !3:2*
            (go off and edit)
            /* repeat last command */
            %5 !!
            (go off and edit)
            /* remove the 1st argument of the command 2 before the current one */
            %6 rm !-6:^


        History  substitution here is a compatible subset of the C-shells
        history substitution  facility.    Cshell  allows  even   weirder
        combinations.


        3.  Multiple  commands  on  one  command line - Command lines are
        split at  semicolons.


        example


            %0 ls -l *.c ; make shell.exe ; exit


        4. Character escapes and argument quoting - i.e.  '\;' suppresses
        the command  parser  from  seeing  the  semicolon  as  a  command
        seperator.


        Quotes are handles thusly:


            1.  String  surrounded  by  single quotes are stripped of the
            single quotes, and passed without wild-card expansion to  the
            invoked program.


            2.  Strings  surrounded  by double quotes are passed complete
            with quotes to the calling program.   This  was  done  for  a
            version  of grep that I have that accepts regular expressions
        with embedded blanks within double quotes.


        5. Many builtin commands.


            a:              b:              c:              cat
            cd              chdir           chmod           cls
            commands        copy            cp              copy
            d:              del             dir             e:
            echo            era             erase           error
            exit            f:              fgrep           g:
            h:              hist            history         i:
            j:              ls              md              mkdir
            more            mv              no history      popd
            pushd           pwd             rd              rm
            rmdir           set             tee             touch
            y


        There are many that are simply aliases, e.g.    'copy'  and  'cp'
        invoke the same program.


        6. commands description syntax


            terms used in syntax explanations :

            fname ::= PC-DOS ambiguous or unambiguous file or directory name.










            uname ::= unambiguous PC-DOS file or directory name

            string ::= any string of printable characters of arbitrary(<512) length.

            filelist ::= filename [filename .. filename]

            noargs ::= no arguments at all

            {arg} ::= term is optional

            envstring ::=    <string>=<string>


        7. command syntax


        drive
            a: | b: | c: | d: | e: | f: | g: | h: | i: | j: <noargs>


            changes default  drive.    If  you  don't  have such a drive,
            nothing happens.


        cat
            cat {<filelist>}


            copies specified files to  standard  output.    If  none  are
            given, copies standard input to standard output


        cp
            cp | copy <filelist> <uname>


            copies specified  files  to  destination  file or device.  If
            more than one file is in the file list,  <uname>  must  be  a
            directory.


        cd
            cd | chdir <dirname>


            makes <dirname> the current default directory.


        chmod
            chmod {-|+[rwh]*} <filelist>


            change file permissions for specified files


            +r, -r turn on or off read permission - i.e. hide the file.
            +w, -w turn on or off write permission.
            +h, -h turn on or off hidden attribute - converse of r
            +a, -a turn on or off archive attribute


            Note  that '-r' or '+rwh' are both valid syntax for switches.
            Also new permission switches  are  permissable  between  file
            names  with  the  following  warning: I don't reset the masks
            between file names - if you have a second batch of  attribute
            changes on  the  command  line,  the  effect is additive.  If
            you're not  careful,  you  could  make  a  mess  of  a  files
            attributes.


            If  you don't specify any attribute switches, file attributes
            will be set  to  0,  which  means  read,write,not  hidden,not









            system, not  modified since last backup.


        cls
            cls | clear <noargs>


            clears the screen and homes the cursor.


        commands
            commands <noargs>


            prints a table of available built-in commands.


        del
            del


            synonym for rm.


        dir
            dir


            synonym for ls.


        echo
            echo <anything>


            echos argument list to screen.


        era
            era


            synonym for rm.


        error
            error <noargs>


            prints returned value of last command to the screen.


        exit
            exit <noargs>


            terminates execution of the shell.


        fgrep
            fgrep <pattern> <filelist>


            looks for unambiguous pattern <pattern> in <filelist>.  echos
            lines matching to the screen.


        hist
            hist | history <noargs>


            prints history list to standard output.


        ls
            ls | dir {-[alqcr]} <filelist>


            Lists files that match <filelist>










            -a all  files,  including  system  files are listed.  '.' and
            '..' are suppressed, but you know they're there if  you  need
            them, don't you?
            -l prints out file times, permissions, etc
            -q suppresses header line from display - useful when you want
            to pipe stuff into another program.
            -c print as one column.
            -r recurse through all encountered subdirectories.


        md
            md | mkdir <uname>


            make a directory.  Prints an error if it can't be done


        more
            more {-[0-9]*} {<filelist>}


            List file to screen with pauses


            -n  specify  tab  width  when  expanding  tabs, where n is an
            integer.  more acts like 'cat'  when  redirected  -  you  can
            concatenate files  in this manner.  If no files are specifed,
            standard input is 'mored.'


        mv
            mv <filelist> <uname>


            moves specified file or files to target specifed by  <uname>.
            If  there  is  more  than one file in list, <uname> must be a
            directory


        popd
            popd <noargs>


            returns to directory at top of directory stack.


        pushd
            pushd <uname>


            save  current  working  directory  on  directory  stack,  and
            changes current working directory to <uname>.


        pwd
            pwd


            prints current working directory to standard output.


        rd
            rd | rmdir <uname>


            remove specified directory if possible.


        rm
            rm {-q} <filelist>


            blows  away all files in <filelist>. If -q is specified, will
            ask if they should be removed.










        set
            set {<envstring> {<envstring> .. <envstring>}}


            sets a string in the environment.   If  you  specify  'name='
            with   no   string   after,   it  will  remove  it  from  the
            environment.  If you don't specify a string, set  prints  out
            current environment.


        tee
            tee <uname>


            Copies  standard  input to standard output, depositing a copy
            in <uname>


        touch
            touch <filelist>


            Makes the modification time of specified  files  the  current
            date and time.


        y
            y <filelist>


            copies standard input to standard output, and then copies the
            specified files  to standard output.  Sort of the opposite of
            tee, in other words.


        7. Helpful hints


            Use forward slashes in all path names - they get converted to
            back slashes before  dos  hears  about  them.    If  you  are
            invoking a program that expects forward slashes (dos external
            commands frinstance) precede it with a back slash.


            put  single  quotes around arguments with semicolons in them,
            so they don't turn into command delimiters.


            The set command affects only the local  shell's  environment.
            You can 'exit' to command.com and the original environment is
            intact.   The  local  environment  is  4K  large  -  which is
            useful.


            Exit and re-invoke if you have trouble loading large programs
            from it - shell dynamically allocates and  frees  memory  all
            the  time,  but the AZTEC run-time doesn't tell DOS to shrink
            memory


        8. Implementation notes


            DOS doesn't acknowledge  a  'change  default  drive'  command
            until you issue  a  'get  current directory' call.  Why?  The
            only way I figured this out is by disassembling command.com.


            This was developed with AZTEC C by MANX.  In  it  are  a  few
            hacked  up  pieces  of  AZTECS library source, which I hereby
            acknowledge.  If MANX has  a  problem  with  me  distributing
            them,  they  can  call  me direct - I figure I'm doing them a
            favor by disseminating this program  as  an  example  of  the









            power and quality of their compiler and development tools.


            If  you  have  the AZTEC compiler and MANX's version of make,
            you can recreate the shell  from  source,  by  using  arc  to
            unpack everything into a directory, editing the macros BINDIR
            and CLIB  and then making  shell.com.  I wouldn't try it with
            any other compiler, because I make a lot of  calls  to  AZTEC
            specific routines.    You can write your own commands and add
            them  by  editing  cmds.c,  and  putting  the  name  of  your
            subroutine and its associated command string into the builtin
            array.


            You  can  safely  modify  any  of my builtins, as long as you
            don't assume that all of your static variables are  going  to
            stay initialized to startup values.


            Any  of the other code (main.c, fexecvp.c fexecv.c) modify at
            your own peril.  I break them every time I do it, and I wrote
            them!!!


            PC|MS-DOS has a limit of 20 file  handles.    If  you  add  a
            command  that opens files, make sure you catch the ctrl-break
            signal and close them.  Look at CAT.C or Y.C for examples.


        9. BUGS
            External DOS commands have trouble parsing the  command  line
            when invoked from   shell.  The command line gets garbled.  I
            spent a lot of time trying to figure this problem out  to  no
            avail.  They apparently get their command line arguments some
            way that  is a mystery to me.  The only solution is either to
            either run command.com, or 'exit'  to  the  original  command
            prompt.


            This  problem  has  kept  me  from running this as a straight
            command.com   replacement.    It  just  goes  to  show   that
            Microsoft and IBM have one hell of a time following their own
            rules.


            Programs  compiled  by  AZTEC  C  that don't set up their own
            signal  handlers  seem  to  be  'unbreakable'  -  you   can't
            ctrl-break  out  of  them, as though SIGINT is set to SIG_IGN
            before entry.  You might not want to invoke such a program if
        it lasts hours and you want to be able to break out of it.


        QUESTIONS COMMENTS GOTO
        KENT WILLIAMS
        NORAND INC.
        550 2nd ST. S.E.
        Cedar Rapids Iowa 52401
        [phone] (HOME VOICE)