FvwmPerl − the fvwm perl manipulator and preprocessor

FvwmPerl should be spawned by fvwm(1) for normal

     To run this module, place this command somewhere in the

         Module FvwmPerl [params]


         ModuleSynchronize FvwmPerl [params]

     if you want to immediately start to send commands to

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

     −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 option.

     −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 one 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 embedded 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 however 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

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

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 another line, is perl code.

    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

    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 recursion.

    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 substituted.

    %Repeat count
        Causes the following lines to be repeated count

    %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



            %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 preprocess).

    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

    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 minute:

        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 operations.

    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 finished.

    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

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 <migo@homemail.com>.