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       FvwmPerl - the fvwm perl manipulator and preprocessor


       FvwmPerl should be spawned by fvwm(1) for normal functionality.

       To run this module, place this command somewhere in the configuration:

           Module FvwmPerl [params]


           ModuleSynchronize FvwmPerl [params]

       if you want to immediately start to send commands to FvwmPerl.


       This module is intended to extend fvwm commands with the perl scripting
       power.  It enables to embed perl expressions in the fvwm config files
       and construct fvwm commands.


       If you want to invoke the unique and persistent instanse of FvwmPerl,
       it is suggested to do this from the StartFunction.  Calling it from the
       top is also possible, but involves some issues not discussed here.

           AddToFunc StartFunction I Module FvwmPerl

       There are several command line switches:

       FvwmPerl [ --eval line ] [ --load file ] [ --preprocess [ --quote char
       ] [ --winid wid ] [ --cmd ] [ --nosend ] [ --noremove ] [ line | file ]
       ] [ --export [names] ] [ --stay ] [ --nolock ] [ alias ]

       Long switches may be abbreviated to short one-letter switches.

       -e|--eval line - evaluate the given perl code

       -l|--load file - evaluate perl code in the given file

       -p|--preprocess [ file ] - preprocess the given fvwm config file

       The following 5 options are only valid together with --preprocess

       -c|--cmd line - an fvwm command to be preprocessed instead of file

       -q|--quote char - change the default ’%’ quote

       -w|--winid wid - set explicit window context (should begin with digit,
       may be in oct or hex form; this window id overwrites implicit window
       context if any)

       --nosend - do not send the preprocessed file to fvwm for Reading, the
       default is send. Useful for preprocessing non fvwm config files.

       --noremove - do not remove the preprocessed file after sending it to
       fvwm for Reading, the default is remove. Useful for debugging.

       -x|--export [names] - define fvwm shortcut functions (by default, two
       functions named "Eval" and ".").  This option implies --stay.

       -s|--stay - continues an execution after --eval, --load or --preprocess
       are processed.  By default, the module is not persistent in this case,
       i.e. --nostay is assumed.

       --nolock - when one of the 3 action options is given, this option
       causes unlocking fvwm immediately. By default the requested action is
       executed synchronously; this only makes difference when invoked like:

           ModuleSynchronous FvwmPerl --preprocess someconfig.ppp

       If --nolock is added here, ModuleSynchronous returns immediately. Note
       that Module returns immediately regardless of this option.


       Aliases allow to have several module invocations and work separately
       with all invocations, here is an example:

           ModuleSynchronous FvwmPerl FvwmPerl-JustTest
           SendToModule FvwmPerl-JustTest eval $a = 2 + 2; $b = $a
           SendToModule FvwmPerl-JustTest eval cmd("Echo 2 + 2 = $b")
           KillModule FvwmPerl FvwmPerl-JustTest


       One of the effective proprocessing solutions is to pass the whole fvwm
       configuration with embeded perl code to "FvwmPerl --preprocess". An
       alternative approach is to write a perl script that produces fvwm
       commands and sends them for execution, this script may be loaded using
       "FvwmPerl --load". There are hovewer intermediate solutions that
       preprocess only separate configuration lines (or alternatively, execute
       separate perl commands that produce fvwm commands).

       The following code snippet adds ability of arithmetics and string
       scripting to certain lines that need this. To use this, you want to
       start FvwmPerl as your first command so that other commands may be
       asked to be preprosessed.

           ModuleSynchronize FvwmPerl

           AddToFunc .
           + I SendToModule FvwmPerl preprocess -c -- $*

           . Exec exec xterm -name xterm-%{++$i}%   # use unique name

           . GotoDesk 0 %{ $[desk.n] + 1 }%         # go to next desk

           . Exec exec %{ -x "/usr/bin/X11/aterm" ? "aterm" : "xterm" }% -sb

           # center a window
           Next (MyWindow) . Move \
             %{($WIDTH - $[w.width]) / 2}%p %{($HEIGHT - $[w.height]) / 2}%p

           . Exec exec xmessage %{2 + 2}%           # simple calculator

           . %{main::show_message(2 + 2, "Yet another Calculator"); ""}%


       There are several actions that FvwmPerl may perform:

       eval perl-code
           Evaluate a line of perl code.

           A special function cmd("command") may be used in perl code to send
           commands back to fvwm.

           If perl code contains an error, it is printed to the standard error
           stream with the [FvwmPerl][eval]: header prepended.

       load file-name
           Load a file of perl code. If the file is not fully qualified, it is
           searched in the user directory $FVWM_USERDIR (usually ~/.fvwm) and
           the system wide data directory $FVWM_DATADIR.

           A special function cmd("command") may be used in perl code to send
           commands back to fvwm.

           If perl code contains an error, it is printed to the standard error
           stream with the [FvwmPerl][load]: header prepended.

       preprocess [-q|--quote char] [-c|--cmd] [line | file]
           Preprocess fvwm config file or (if --cmd is given) line. This file
           contains lines that are not touched (usually fvwm commands) and
           specially preformatted perl code that is processed and replaced.
           Text enclosed in %{ ... }% delimiters, that may start anywhere on
           the line and end anywhere on the same or an other line, is perl

           The quote parameter changes perl code delimiters.  If a single char
           is given, like ’@’, the delimiters are @{ ... }@. If the given
           quote is 2 chars, like <>, the quotes are <{ ... }>

           The perl code is substituted for the result of its evaluation. I.e.
           %{$a = "c"; ++$a}% is replaced with "d".

           The evaluation is unlike eval and load is done under the package
           PreprocessNamespace and without use strict, so you are free to use
           any variable names without fear of conflicts. Just don’t use
           uninitialized variables to mean undef or empty list (they may be in
           fact initialized by the previous preprocess action), and do a
           clean-up if needed. The variables and function in the main package
           are still available, like ::cmd() or ::skip(), but it is just not a
           good idea to access them while preprocessing.

           There is a special function include(file) that loads a file,
           preprocesses it and returns the preprocessed result. Avoid

           If any embedded perl code contains an error, it is printed to the
           standard error stream and prepended with the
           [FvwmPerl][preprocess]: header. The result of substitution is empty
           in this case.

           The following variables may be used in the perl code:


           The following line based directives are recognized when
           preprocessing. They are processed after the perl code (if any) is

           %Repeat count
               Causes the following lines to be repeated count times.

           %ModuleConfig module-name [ destroy ]
               Causes the following lines to be interpreted as the given
               module configuration. If "destroy" is specified the previous
               module configuration is destroyed first.

           %Prefix prefix
               Prefixes the following lines with the quoted prefix.

           %End any-optional-comment
               Ends any of the directives described above, may be nested.


               %Prefix "AddToFunc SwitchToWindow I"
                   Iconify off
                   WindowShade off
                   WarpToWindow 50 50

               %ModuleConfig FvwmPager destroy
                   Colorset 0
                   Font lucidasans-10
                   DeskTopScale 28
               %End ModuleConfig FvwmPager

               %Prefix "All (MyWindowToAnimate) ResizeMove "
               100 100 %{($WIDTH - 100) / 2}% %{($HEIGHT - 100) / 2}%
               %Repeat %{$count}%
               br w+2c w+2c w-1c w-1c
               %Repeat %{$count}%
               br w-2c w-2c w+1c w+1c
               %End Prefix

           Additional preprocess parameters --nosend and --noremove may be
           given too. See their description at the top.

       export [func-names]
           Send to fvwm the definition of shortcut functions that help to
           activate different actions of the module (i.e. eval, load and

           Function names (func-names) may be separated by commas or/and
           whitespace. By default, two functions "Eval" and "." are assumed.

           The actual action defined in a function is guessed from the
           function name if possible, where function name "." is reserved for
           preprocess action.

           For example, any of these two fvwm commands

              SendToModule MyPerl export PerlEval,PP
              FvwmPerl --export PerlEval,PP MyPerl

           define the following two shortcut functions:

             DestroyFunc PerlEval
             AddToFunc I SendToModule MyPerl eval $*
             DestroyFunc PP
             AddToFunc I SendToModule MyPerl preprocess -c -- $*

       These 4 actions may be requested in one of 3 ways: 1) in the command
       line when FvwmPerl is invoked (in this case FvwmPerl is short-lived
       unless --stay or --export is also given), 2) by sending the
       corresponding message in fvwm config using SendToModule, 3) by calling
       the corresponding perl function in perl code.


       There are several functions that perl code may call:

           In case of eval or load - send back to fvwm a string $fvwm_command.
           In case of preprocess - append a string $fvwm_command to the output
           of the embedded perl code.

           This function is equivalent to the eval functionality on the string
           $perl_code, described above.

           This function is equivalent to the load functionality on the file
           $filename, described above.

       preprocess(@params, ["-c $command"] [$filename])
           This function is equivalent to the preprocess functionality with
           the given parameters and the file $filename described above.

       export($func_names, [$do_unexport])
           This function is equivalent to the export functionality with the
           given $func_names, described above. May also unexport the function
           names if the second parameter is true.

           Function names should be separated by commas or/and whitespace. If
           $func_names is empty then functions "Eval" and "." are assumed.

           Terminates the module.

           Skips the rest of the event callback code, i.e. the module returns
           to listen to new module events.

           Unsynchronizes the event callback from fvwm. This may be useful to
           prevent deadlocks, i.e. usually fvwm kills the non-responding
           module if the event callback is not finished in ModuleTimeout
           seconds. This prevents it.

           This example causes FvwmPerl to suspend its execution for one

               SendModule FvwmPerl eval unlock(); sleep(60);

           However, verify that there is no way a new message is sent by fvwm
           while the module is busy, and fvwm stays locked on this new message
           for too long. See also the detach solution if you need long lasting

           Forks and detaches the rest of the event callback code from the
           main process. This may be useful to prevent killing the module if
           its event callback should take a long time to complete and it may
           be done in the detached child. The detached child may still send
           commands to fvwm (don’t rely on this), but not receive the events
           of course, it exits immediately after the callback execution is

           If you use detach(), better only send commands to fvwm in one
           process (the main one or the detached one), doing otherwise may
           often cause conflicts.

       show_message($msg, $title[, $use_stderr_too=1])
           Shows a dialog window with the given message, using whichever X
           tool is found in the system.

           See FVWM::Module::Toolkit::show_message for more information.


       There are several global variables in the main namespace that may be
       used in the perl code:

           $a, $b, ... $h
           @a, @b, ... @h
           %a, %b, ... %h

       They all are initialized to the empty value and may be used to store a
       state between different calls to FvwmPerl actions (eval and load).

       If you need more readable variable names, either write "no strict
       ’vars’;" at the start of every perl code or use a hash for this, like:

           $h{id} = $h{first_name} . " " . $h{second_name}

       or use a package name, like:

           @MyMenu::terminals = qw( xterm rxvt );
           $MyMenu::item_num = @MyMenu::terminals;

       There may be a configuration option to turn strictness on and off.


       FvwmPerl may receive messages using the fvwm command SendToModule. The
       names, meanings and parameters of the messages are the same as the
       corresponding actions, described above.

       Additionally, a message stop causes a module to quit.

       A message unexport [func-names] undoes the effect of export, described
       in the ACTIONS section.

       A message dump dumps the contents of the changed variables (not yet).


       A simple test:

           SendToModule FvwmPerl eval $h{dir} = $ENV{HOME}
           SendToModule FvwmPerl eval load($h{dir} . "/test.fpl")
           SendToModule FvwmPerl load $[HOME]/test.fpl
           SendToModule FvwmPerl preprocess config.ppp
           SendToModule FvwmPerl export Eval,PerlEval,PerlLoad,PerlPP
           SendToModule FvwmPerl unexport PerlEval,PerlLoad,PerlPP
           SendToModule FvwmPerl stop

       The following example handles root backgrounds in fvwmrc. All these
       commands may be added to StartFunction.

           Module FvwmPerl --export PerlEval

           # find all background pixmaps for a later use
           PerlEval $a = $ENV{HOME} . "/bg"; \
             opendir DIR, $a; @b = grep { /xpm$/ } readdir(DIR); closedir DIR

           # build a menu of background pixmaps
           AddToMenu MyBackgrounds "My Backgrounds" Title
           PerlEval foreach $b (@b) \
             { cmd("AddToMenu MyBackgrounds '$b' Exec fvwm-root $a/$b") }

           # choose a random background to load on start-up
           PerlEval cmd("AddToFunc \
             InitFunction + I Exec exec fvwm-root $a/" . $b[int(random(@b))])


       SendToModule just like any other fvwm commands expands several dollar
       prefixed variables.  This may clash with the dollars perl uses. You may
       avoid this by prefixing SendToModule with a leading dash. The following
       2 lines in each pair are equivalent:

           SendToModule FvwmPerl eval $$d = "$[DISPLAY]"
           -SendToModule FvwmPerl eval $d = "$ENV{DISPLAY}"

           SendToModule FvwmPerl eval \
               cmd("Echo desk=$d, display=$$d")
           SendToModule FvwmPerl preprocess -c \
               Echo desk=%("$d")%, display=%{$$d}%

       Another solution to avoid escaping of special symbols like dollars and
       backslashes is to create a perl file in ~/.fvwm and then load it:

           SendToModule FvwmPerl load build-menus.fpl

       If you need to preprocess one command starting with a dash, you should
       precede it using "--".

           # this prints the current desk, i.e. "0"
           SendToModule FvwmPerl preprocess -c Echo "$%{$a = "c"; ++$a}%"
           # this prints "$d"
           SendToModule FvwmPerl preprocess -c -- -Echo "$%{"d"}%"
           # this prints "$d" (SendToModule expands $$ to $)
           SendToModule FvwmPerl preprocess -c -- -Echo "$$%{"d"}%"
           # this prints "$$d"
           -SendToModule FvwmPerl preprocess -c -- -Echo "$$%{"d"}%"

       Again, it is suggested to put your command(s) into file and preprocess
       the file instead.


       FvwmPerl being written in perl and dealing with perl, follows the
       famous perl motto: "There’s more than one way to do it", so the choice
       is yours.

       Here are more pairs of equivalent lines:

           Module FvwmPerl --load "my.fpl" --stay
           Module FvwmPerl -e 'load("my.fpl")' -s

           SendToModule FvwmPerl preprocess --quote '@' my.ppp
           SendToModule FvwmPerl eval preprocess({quote => '@'}, "my.ppp");

       Warning, you may affect the way FvwmPerl works by evaluating
       appropriate perl code, this is considered a feature not a bug.  But
       please don’t do this, write your own fvwm module in perl instead.


       The fvwm(1) man page describes all available commands.

       Basically, in your perl code you may use any function or class method
       from the perl library installed with fvwm, see the man pages of perl
       packages General::FileSystem, General::Parse and FVWM::Module.


       Mikhael Goikhman <>.