Club Amiga de Montreal - CAM/CAM_CD_1.iso/files/308.lha/treewalk/treewalk.doc

Text File | 1980-12-05 | 12.3 KB | 292 lines

SYNOPSIS:

Treewalk - visit all the files in a directory tree.

usage: treewalk [<options>] [[command] <CLI command>]

options are: post, both, dir <directory>, verbose, single, filter <expression>

options and "command" are only checked in the first 3 characters.

DESCRIPTION:

Treewalk is a command for visiting all the files of a subtree of an
AmigaDOS file system. It's designed to be reasonably fast, robust, and
not use a lot of stack space - or any other critical resources. About
the only thing you're liable to run out of is memory.  (Note: "all the
files of a subtree" doesn't include the directory that's the root. So
if you do something to every directory in the subtree, it won't do it
to the root directory.

The normal behavior of the command is to test every file in the
specified subtree against a user "filter" expression, and if the file
passes through the filter, to issue the user supplied command with
that file as one of the arguments.

Any argument that isn't an option starts the user supplied command.
All arguments after the first command argument are concatenated
together, with a single space between them, to make up the command. As
each file is visited, its full path name enclosed in '"''s (so that
things like RAM DISK: will work) is concatenated to the end of the
command. When the last file is visited, or the command line becomes to
long for the system, it is issued to the cli. The current working
directory of the command is the directory in which the treewalk
command was started, not the directory being visited or the directory
that is the root of the tree being walked. The command is run as many
times as needed so that all files are visited.

The "command" keyword indicates that the next argument is the start of
the command, whether or not it looks like a keyword. This is useful if
the command you wish to run on the starts with a valid keyword. If
there is no command, treewalk will print out the names of all files
that pass through the filter.

The "verbose" option causes treewalk to print the text of every
command before issuing it.

The "ignore" option causes treewalk to not print anything on error
returns from the command.

The "single" option defeats the stacking of files on the command line,
and the command is run once for every file. This is useful if the
command in question only accepts one filename.  For instance, "list
nohead" should be done this way.

The "dir" option is followed by the name of a directory. That
directory will then be used as the root of the tree, instead of the
current directory.

Normally, treewalk will visit a directory before it visits any of
it's children. This is a "preorder" treewalk, "pre" because it
visits parents first. You can change this with the following
options.

The "post" option causes treewalk to visit all the children of a
directory before it visits that directory.

The "both" option causes treewalk to visit a directory both before and
after it visits all the children of that directory. If the directory
has no subdirectories, then it will list all the files of that
directory twice, one listing following immediately after another.

The "filter" option is used to specify the filter expression. If no
filter is provided, all files in the subtree will pass.

The filter expression is similar to a C language expression, Like a C
expression, it is false if it evaluates to 0, and true otherwise. The
only variables in the expression are parts of the FileInfoBlock of the
file being evaluated. They are:

diskkey        - for gurus only
direntrytype    - ditto
entrytype    - ditto
filename    - the name of the file in this directory (string value)
name        - the full path name of the file (string value)
protection    - the protection mask
size        - the number of bytes in the file
numblocks    - the number of blocks in the file
date        - date the file was last changed
day        - day the file was last changed
comment        - comment associated with the file (string value)

The "day" version of date ignores the minutes of the day of creation,
so that it will compare equal to a day with no time specified via the
"`" construct.  I.e., "day == `yesterday`" matches files created
yesterday.

Note to purists: The "date" value is the number of minutes since
midnight, January 1, 1978. It's called "date" instead of "datestamp"
because it's not a real datestamp.  The protection bits `rewd` are
inverted on output, as they have inverted meaning: the `r` bit being
on means you _can't_ read the file. List prints a `r` when you can
read the file. These bits are inverted to prevent the user from having
to remember this.

The FileInfoBlock values can also be gotten for other files. The same names
as above are used, preceded by a file name and a '.'. For instance,
main.c.size is the size of the file "main.c" in the directory treewalk
was started in. Such expressions are evaluated at startup time, and
are constant throughout the execution of treewalk.

The other valid constants in filter expressions are:

true        - longhand for 1
false        - longhand for 0
integers    - The same as C:
            starting with a '0' indicates octal
            starting with a '0x' indicates hex
            otherwise, it's decimal
"string"    - a text string
'string'    - ditto

In addition any string surrounded by "`"'s is an integer constant, of
one of two forms. If it consists of a string of characters from the
set "rwdespah", then the appropriate bits will be turned on to match
the protection of the file.

Otherwise, this may be a date and time specifier. These are of the
form "day minute". Day is either a fully specified numeric date of the
form "month/day/year", a day of the week, "yesterday", or not
specified. The "month/day/year" form uses a two-digit year between
1978 & 1999. The day of the week refers to the previous day of that
name. If the day is not specified, then today is used.

Time is either "noon", hour:minute on a 24-hour clock, or
missing. If the time is missing, then midnight is assumed.  If
the day specified is today, and the time is later than the
current time, then yesterday is assumed - even if you specify
the day explicitly.

There are some operands that depends on the file currently being
filtered, or on the user. They are:

dir    - true if the current file is a directory, else false
file    - the opposite of dir
name    - the full path name of the file (string value)
user    - name is printed on the console, followed by a ?, and a line
        is read. If the first character of the line is 'y' or
        'Y', then true, otherwise false.

Finally, any non-string not recognized is assumed to be an ARexx macro
name. The extension used in searching for the macro is "ftw".  This
macro will be invoked as a function with pathname of the directory as
it's first argument, and the file name as it's second.  The pathname
will be in a form such that "arg(1) || arg(2)" will be the full
pathname. The expression the macro returns should be an integer, and
will be used as the value of the macro token in the expression.

The macro may issue "commands" back to the running treewalk. The
commands are treated as filters, and the current file is sent through
them, and the result returned. What the result is depends on whether
you have specified "options results". If this is not on, the rc is 0
if the filter returns "true", and 1 if the filter returns "false". If
the results option is on, and no errors occured, rc is always 0, and
the result string is the value, formated as four bytes of hex. You can
then use x2c() and import() to extract strings, if the value returned
was a string (i.e. - you issued the command 'comment'). In either
case, return codes greater than 1 indicate a real error - usually in
the filter expression, sometimes that you're out of memory.

As a suggestion for writing ftw macros, I recommend following the rule
that if the macro uses the file name, it returns a 1, and if it
rejects the file name, it returns a 0. This allows treewalk to print
the names of the files used by the macro by 'treewalk filter macro',
or to not print the names by 'treewalk filter "macro & false"'. Of
course, if the macro is just a filter itself, then it should return
either 0 or 1.

To combine these, there are the operators. All but four are from C,
and the precedence of the operators is the same as C. They are:

!    - unary logical not;        ~            - unary bitwise not
&    - bitwise and
%    - bitwise exclusive or
|    - bitwise or
=*, =#, !*, !# - string compares    <, >, <=, >=, ==    - integer comparisons
&&    - logical and, short circuiting
||    - logical or, short circuiting

(, )    - parens for grouping


The only four operators not found in C are =*, =#, !* and !#. These
are pattern matching operators for use on strings (file names or
comments). The left-hand operand is a string, the right-hand operand
is a pattern. =* and !* provides Unix-like regular expressions, with
'*' and '?' having special meaning. =# and !# provides AmigaDOS like
regular expressions, with '#' and '?' having special meanings. =* and
=# are true if the comparisons match, and !* and !# are true if the
comparisons don't match.

The rest of the operators behave as one would expect them to. The
only thing that needs to be pointed out is that logical and (or)
short circuits. So if the left-hand operand is false (true), the
right-hand operand is never evaluated. This allows a limited form of
flow control in the filter expression.

Like C, it is legal to apply the logical operators to non-boolean
ints, and to apply the comparison operators to booleans. Unlike C,
strings can not have their addresses extracted, and ints cannot be
used for string addresses. Strings may only appear, and are all that
may appear, as the operands of the pattern matching operators.

As a final suggestion on filters, unless the filter is a single token,
it's probably best to surround it in '"''s, as that will cause the
magic characters in the expression (&, |, <, > come to mind) to not
be interpreted by whatever CLI you are running.

EXAMPLES:

List all the directories in src:

    treewalk dir src: filter dir

Delete the subtree x:

    treewalk dir x post single delete

This isn't really very useful, as "delete all" is faster. However, it
illustrates several points. First, "delete" is broken, as it has a
limited number of arguments. Second, this requires the postorder
treewalk, so that all the files in a directory will be deleted before
the directory is deleted.

Delete all .o files in the current subtree:

    treewalk filter "filename =# '#?.o'" single delete

List all files newer than :last-backup.

    treewalk filter "date > :last-backup.date"

Find all files on the current device older than :last-backup using
over 20 blocks, that don't have the execute bit on, and compress them.

    treewalk dir : filter "date < :last-backup.date &&
        numblocks > 20 && !(protection & `e`)" compress

Same as above, except we also don't compress .o files in the subtree at
:go and we only compress if the user wants us to.

    treewalk dir : filter "name !* '*:go/*' &&
        date < :last-backup.date && numblocks > 20 &&
        !(protection & `e`) && user" compress

This last might more efficiently be done as a Rexx macro that decides
whether or not the file will be compressed, and then asks the user.
Let's assume we've got a macro "munchp.ftw" that does the name, mode
and size checking. You could then do:

    treewalk dir : filter "date < :last-backup.date && munchp
        && user" compress

As an alternative, suppose that instead of compressing them, you
wanted to save them to an archive somewhere, and had a rexx script to
do that. Further, suppose that the Rexx script (archive.ftw) return 1
if it did the archive, and 0 if it didn't. Then you might do:

    treewalk dir : filter "date < :last-backup.date && munchp
        && archive && false"

To quietly do the archiving. Or you might do:

    treewalk >logs:archive.log dir :
        filter "date < :last-backup.date && munchp && archive"

To list the archived files to logs:archive.log.

    Copyright (C) 1989  Mike Meyer

    This file is free documentation; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation; either version 1, or any later version.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with this program; if not, write to the Free Software
    Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.