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Debian Menu System
Chapter 6 The internals of the menu package

6.1 The update-menus program

On startup, update-menus checks the file /var/run/update-menus.pid and the pid in it. If there's an update-menus process with that pid it kills it. If /var/lib/dpkg/lock exists, it forks to background and returns control to dpkg. The background process checks the /var/lib/dpkg/lock file approx. every second until the file's gone.

After that, update-menus reads the menu-entry-files in the following directories:/etc/menu /usr/lib/menu /usr/lib/menu/default (if a user runs update-menus, it will add ~/.menu to the front of that list). For every menu entry line in each file it checks if the corresponding package is installed (works on file bases for old syntax menu entry files). The menu entries of all "installed" packages are added together in one big buffer that is kept in memory (exception: executable menu entry files are executed, and stdout is placed in the buffer).

Once it's read all menu entry files, update-menus starts all executable scripts in /etc/menu-methods/, hands the scripts the previously created buffer via stdin. (If update-menus is ran by a user, it will first try to run the scripts in ~/.menu-methods, and only if that directory doesn't exist, it will run the scripts in /etc/menu-methods).

Note that as an aid to debugging, one can create a simple script like

     #!/bin/sh
     cat > /tmp/menu-stdout

and then view the file /tmp/menu-stdout to see exactly what update-menus handed the menu-methods on their stdin.

This may also be useful for people writing /etc/menu-method/* scripts: Running update-menus every time you changed something in the script may be quite time-consuming. So, it's much easier to install the above script in /etc/menu-methods/, run update-menus once, and then run

       /etc/menu-methods/mymethod < /tmp/menu-stdin

(and, if that also takes too long, just try editing /tmp/menu-stdin, and removing 90% or so of all entries)

6.2 The install-menu program

The files /etc/menu-methods/$wm are executable config files that start with the line

       #!/usr/sbin/install-menu

and thus start that program, handing it the configuration file for the specific window manager in the first command line argument. This configuration consists of:

1. the compatibility mode ("menu-1" or "menu-2").

2. where the various files should be stored/read.

3. what "needs" are supported, and what wrapper files should be used for each "type".

See /usr/doc/menu/examples/ of the menu package for more comments.

Options to install-menu:

       -v              be verbose
       -d              Produce loads of debugging output

Some window managers don't support an `include' like statement in their system.*rc files (like m4 or cpp preprocessing), they cannot read the menudefs.hook file generated by install-menu from their system.*rc config file. To still be able to use them, install-menu will copy the file $path/$examplercfile to $path/$rcfile (with $examplercfile and $rcfile defined in the install-menu config file, and $path eihter the $rootprefix or ${HOME}/userprefix, depending on whether root or user executed the file.), and replace all occurrences of ``install-menu-defs'' with the $genmenu file it just generated.

As an example, consider the following: examplercfile=system.foo-wm-example, rcfile=system.foo-wm, genmenu=menudefs.hook and rootprefix=/etc/X11/foo-wm. Now, if install-menu gets run, it will first generate the file /etc/X11/foo-wm/menudefs.hook. Next, it will line-by-line read the file /etc/X11/foo-wm/system.foo-wm-example and copy it's contents to /etc/X11/foo-wm/system.foo-wm, replacing every occurrence of the string install-menu-defs by the contents of the file /etc/X11/foo-wm/menudefs.hook.

To activate the file copying in this way, simply define the $examplercfile and $rcfile variables in the install-menu configuration file (for example, see /etc/menu-methods/fvwm), and make sure there is a $path/$examplercfile ($path being either $rootprefix, or $userprefix.)

If you are wringing a menu method, you can use the following to debug it somewhat easier:

1. use the "cat" menu-method in /usr/doc/menu/examples/cat to create a list of menu entries in /tmp/menu-stdin (put it in ~/.menu-methods, and run update-menus), and then

2. you can run just your menu-method with (if it's called wm):

          ./wm -v < /tmp/menu-stdin
   

   (Use -v for verbose, -d for debugging, and you'll get loads of output!)

6.3 The install-menu config script definitions

The menu-methods in /etc/menu-methods/* are basically made up of a lot of ``tag=string'' definitions, explaining install-menu how to generate a system.$wmrc script. This way you can tune the look of generated system.$wmrc to your needs.

In the following, something like

       treewalk="c(m)"

means that the treewalk variable by default has the value "c(m)".

For examples of what these scripts can look like, see /usr/doc/menu/examples/*.

compat="menu-1"

Should always be "menu-1". Please, make this the first non-comment line in the script.

supported

endsupported

Between the supported and endsupported keywords you define what "needs" are supported by this window manager. So, the following is an example for a wm that supports both needs=x11 and needs=text:

       supported
         x11=" ShowEntry(\"" $title "\", \"" $command "\")"
         text="  ShowEntry(\"" $title "\", \"" $command 
                  "xterm -T " $title " -e " $command "\")"
       endsupported

For the variable substitution (and functions, not shown above), see the next paragraph. In the above example, you'll notice that for the menu entries that "need=text", an xterm is spawned for the command to run in. Also, as x11 is higher up in the supported list above than text, a package that supplies both a "needs=x11" and a "needs=text" entry will have the needs=x11 entry installed, in favour of the needs=text entry. You can continue lines on the next line with a \, but do make sure you don't add any spaces after the \.

startmenu=""

endmenu=""

submenutitle=""

These define what to print for the beginning/end of a menu, and how to the print a menu entry that pops up another menu entry. They are substituted the same way as the "supported" stuff is. (see next paragraph).

treewalk="c(m)"

This string defines in what order to dump the $startmenu, $endmenu, and $submenutitle (and its children). Each char in the string refers to:

         c  : dump children of menu.
         m  : dump this menu's $submenutitles
         (  : dump $startmenu
         )  : dump $endmenu
         M  : dump all $submenutitles of this menu and this menu's children.

The default is "c(m)". For olvwm, one needs: "(M)"

genmenu=""

The menu file to generate (usually something like system."$wm"rc). The file itself may depend on the level or title that is currently being worked on, like

         genmenu="/subdir/" replacewith($section," ","_") "/rc.menu"

(Substitution works just like in the supported stuff, see above). Note that the files made this way are truncated upon opening, so if you have a genmenu like the example above, then your endmenu= will override the startmenu stuff (but you probably only need one of the two anyway).

rootsection="/Debian"

the prefix, every $section variable gets.

prerun=""

postrun=""

The commands to run before resp. after the actual generation of the menudefs.hook (genmenu) file. Commands will be executed by sh. Example:

       prerun="rm -rf " prefix() "/*"
       postrun="killall -USR1 fvwm2"

(Substitution works just like the supported stuff, see below).

preruntest=""

Just like prerun, but if the return value of the command is non-zero, menu will quit.

also_run=""

If non-zero, install-menus will, after generating the output files, also load the file also_run, and use the new assignments to treewalk, genmenu, etc to generate more output. This second time, variables like prerun and all of the hint stuff are ignored.

Note: NOT just like prerun etc: prerun etc start a command with /bin/sh, also_run doesn't exec any other command, just tells install-menu to also load anoter binary, and generate the output.

onlyrunasroot=false

onlyrunasuser=false

If onlyrunasroot is set to true, menu will quit silently when run as user. Similarly for onlyrunasuser.

preoutput="#Automatically generated file. Do not edit (see /usr/doc/menu/html)\n\n"

postoutput=""

Text to put at the beginning resp. end of the generated file ($genmenu).

command=""

A command to run instead of install-menus. This command used to be needed to get around limitations due to compatibilty stuff. But that compatibility with pre menu-1 stuff has been dropped, and isn't needed any more.

Example:

       command="cat > /tmp/menu-stdin"

hotkeyexclude=""

Keys not to use for hotkey generation. You can use the same variables and functions here as in for example the startmenu sections.

Example:

       hotkeyexclude="q" $section

hotkeycase="insensitive"

can be either "insensitive" or "sensitive". Determines whether the hotkeys can be of mixed case (fvwm2 reads the hotkeys case-insensitive, pdmenu case-sensitive). In case of the titles "Xa" and "xb", hotkey case-insensitive will generate "X" and "b", whereas case-sensitive would generate "X" and "x".

sort=$sort ":" $title

Entries within one menu will be alphabetically sorted by whatever sort returns. So, if you do sort=ifelse($command, "1", "0"):$title, then all submenus will appear above the commands in a submenu. (A submenu always has $command=""). Or, as Joey Hess writes:

       You can add another field to the menu items, with whatever name you like,
       let's say it's called priority. Then add this line to
       /etc/menu-methods/*:
       
       sort=ifelse($priority, $priority, "9")
       
       This has the result of sorting things so items with a low priority sort to the
       top, and items with no priority default to priority 9 and sort to the bottom.
       
       (Note that it compares the strings alphabetically, not numerically.)

rcfile=""

If the window manager doesn't support an "include filename" or "read(filename)" statement in it's config file, you can rename the wm's config file to system."$wm"rc-menu, and insert a "install-menu-defs" line (without the quotes, or whitespace around it, and "install-menu-defs" must be the only thing on the line) in the system."$wm"rc-menu file. This will then get replaced by the $genmenu file that was just created (see also $examplercfile).

examplercfile=""

if needed (see rcfile), this is the system.rc"$wm"-menu file. In that case, make rcfile=system.rc"$wm".

rootprefix=""

The prefix to use when running as root (applies to $genmenu, $rcfile, $examplercfile and other old cache files)

userprefix=""

see rootprefix, but when running as user.

process_menudirs="user,system"

Directories that install-menu will process menu entry files from (new in menu-2.1.6). The default is "user, etc, debian, default", which means that install-menu will read files found in ${HOME}/.menu, then in /etc/menu, then in /usr/lib/menu, and last in /usr/lib/menu/default. To make life easier, there's an alias for the etc, debian, default locations: system. Note that the order in which you specify the locations doesn't matter.

To be complete, user="${HOME}/.menu"; etc="/etc/menu"; debian="/usr/lib/menu"; default="/usr/lib/menu/default"; system="/etc/menu, /usr/lib/menu, /usr/lib/menu/default"

If you have a WM which allows an "incremental" user configuration file (with only the menu entries of the users), then you may want to specify:

     process_menudirs="user, " ifroot(system)

This will cause install-menu to discard all system menu entry files if run as normal user, and the user's WM-config file can #include the system menu definitions from /etc/WM/*. Note that if you do this, you disable an elswehere in this manual advertised feature: if the user does true > ~/.menu/package, then the user doesn't have the menu entry files from package. But as in your case the user's WM-config file #includes the system wide menu defintions, this will not work any more.

The way this feature works may not be the one you at first glance expect: when the user or system admin runs update-menus, it will read all menu entry files in all directories (user, etc, debian and default). update-menus then generates one big list of the concatenated files (whose packages are installed), and hands that file to the stdin of the install-menu program in /etc/menu-methods/*. That program then reads the process_menudirs variable, and starts processing the input given by update-menus. And it will discard any menu entry files if they appear to originate from a directory not specified in process_menudirs. Due to this implementation, it is not possible for install-menu to read menu entry files outside the standard user, etc, debian and default directories, and also the order of the directories in process_menudirs has no effect. Also, as update-menus, when ran under root will not process the user's (root) home dir, so the user setting in process_menudirs will simply have no effect.

repeat_lang=""

If set to "LOCALE", then menu will automatically translate all title's to the languages specified by the current LC_LOCALE setting. (LC_ALL, ...). It is intended to expand this to repeat_lang="en:es:eo:nl", which would repeatedly run install-menus for the various specified languages. But the latter hasn't yet been implemented.

hint_optimize=false

If set to true, menu will try to generate an `optimal' tree, using the variables below. If set to false, menu will keep the sections as they are specified in the menu entry files (and ignore any hint stuff).

hint_nentry=6

Optimal number of entries in a submenu. It's a float, so you can set it to 5.5 if you cannot decide between 5 and 6. Also, values less than 3 probably don't work very well at the moment.

hint_topnentry=5

Same as hint_nentry, but for the top level menu. Often here are other entries, added by the Window Manager itself (like Exit, Xterm, whatever) that menu doesn't know about, so that you may want to instruct menu to put less entries in the top level menu.

hint_mixedpenalty=15.0

Penalty for `mixed' menus. Mixed menus are those with both submenus and direct commands in them.

hint_minhintfreq=0.1

Minimal relative frequency for the hints before they are considered. Internal variable to speed up the tree generation. If you find menu slow, increase this value (to, say 0.2 or 0.3).

hint_mlpenalty=2000

`max local penalty', while evaluating the possible trees, menu gives `penalties' for submenus that don't contain the desired number of submenus. The penalty is sqrt(n_entry_opt-n_entry), and eventually will be calculated as a sum of all nodes. But to speed things up, menu will discard possibilities in which any node has a `local' penalty of more than hint_mlpenalty. Increase this value if you think menu is overlooking your favorite tree (also decrease minhintfreq), decrease this value if you think menu is waisting too much time. Because of hint_max_ntry, the influence of this variable is nearly zero nowadays.

hint_max_ntry=4

menu will recursively, for each node, try the hint_max_ntry best local menu-divisions.

hints_max_iter_hint=5

The search for what hints to use in one menu is rather expensive. But due to the way things are sorted, menu seems to always find the `best' match in the first 2% of iterations. Thus, a way to speedup things is simply to cut of menu searching after `some' iterations are done. This value controls this, and limits the number of iterations to 5+hint_max_iter_hint*number_of_possible_hints. Set this value to negative to disable this.

hint_debug=false

Set to true if you want to see loads and loads of debug output.

6.4 Hints, tree optimization

The hints actually work in a rather strange way: when hint_optimize=true then all $section elements are added to the specified $hints variable, and the order (/Apps/Editors or /Editors/Apps) of the resulting hints is completely ignored. Then, the hints for each menu entry are handed to the optimization routine, that will calculate a reasonable tree for those hints. That tree must comply with the following:

When a user looks for a program "Program" with, say, hints "Good,Bulky,Heaven", then, while walking through the tree, it should at every node visited be clear for the user what submenu to select (or the menu should have "Program" directly in it). So, the toplevel menu may look like

       Good
       Hell
       Microsoft

because then a searcher for a menu entry with hints "Good,Bulky,Heaven" will know to select the submenu "Good". The toplevel menu may not look like

       Good
       Hell
       Heaven

as now it isn't clear whether to visit the Good or the Heaven submenu.

That rule allows usually for many different trees, and the task of the optimization procedure is to select, in a finite amount of time, the tree that best matches the user's desire obout the optimum number of menu entries.

6.5 Variables and functions in the install-menu scripts

The supported "needs" definitions and "startmenu=", "endmenu=" and "submenutitle=" are interpreted as follows:

     String constants:
       Anything inside double quotes ("") is interpreted as a string, and
       is written verbatim to the output file.
       Stuff like \n, \t, ... will be substituted for their C expansions 
       (But not \0xx, currently).
     
     Variables:
       Anything matching $[a-z,A-Z,_]* is interpreted as a variable, and
       the corresponding definition from the menu entry is substituted.
       
       Special variables:
         The following variables are treated in a special way by install-menus,
         either because they are used for other purposes too, or because they
         are modified by install-menus (the ones marked with a "!" are modified
         by install-menus).
         
         needs:   used to determine whether the window manager supports this
                  menu entry.
         command: If this is undefined, this menu entry is taken as defining
                  a sub-menu. (this way you can specify icons of sub-menus).
         title!:  Used for sorting (see section).
                  For sub-menu entries (those with empty command), this
                  is initialised to the last part of the section.
                  Please, keep the title short (two words at maximum).
                  The title is for people who already know what programme
                  they want to start. See "longtitle" and "description" below
                  for longer descriptions.
         sort:    used for sorting (see section). To make sure an entry is
                  at the beginning, use something with a low ASCII number,
                  like "$". For sorting at the end, use "|"
         section!:Used to determine the section of the menu entry.
                  The menu entries that have a empty $command, ie those that
                  define a submenu, have $title added to the end of $section 
                  The menu entries that have a non-empty $command have their
                  $section modified to $section/$title, or $section/$sort:$title
                  if $sort is defined. The menu entries within one submenu
                  are sorted according to $section.
         hotkey!: Modified to reflect what install-menus thinks is the
                  most suitable hotkey for this menu entry. The hotkey=
                  in the menu entry file is taken as a suggestion, that could
                  be overwritten if there is another entry with the same hotkey=.
                  To suggest two possible hotkeys for an entry use
                  hotkey="ab", with "a" being the most preferred hotkey.
     
       Preferred variables:
         The following aren't special for install-menus, but it's nice 
         (read: essential) to use the same variables for the same things.
         So, I'll suggest some here. If you want to invent new ones, please
         do so and mail them to me so that I can include them here.
     
         icon:    The location of the iconfile for this menu entry.
                  If you don't have an iconfile, just leave out the icon=
                  in the menu entry.
         longtitle: For people that like descriptive titles (about one line)
                  It is probably best to include this in your menu entries,
                  while the window-managers don't (by default) put it in the
                  menus. That way, people who want descriptive titles can
                  turn them on, but others don't need to use them.
         description:An even longer description (about 5 lines).
                  For example, a description of the documentation in
                  the dwww generated html pages.
     
       Suggested variables:
         The following variables probably shouldn't appear often (or at
         all) in the menu files supplied with packages. They are mostly
         intended for use by local system managers. Nevertheless, it is
         advised that all debian systems use the following variable names:    
         
         visible: Some apps add entries to utmp the utmp file, so that
                  "who" and friends know they are running (this is
                  especially true for xterms etc). If $visible set
                  (to anything other than "" or "none"), xterms etc will
                  not write logging info to utmp. (may not work for
                  your window manager).
         geometry: For X apps, this will be the size of the (main) window
                  that will be created (units in either chars or pixels,
                  depending on type of main window (xterm or graphic)).
                  If you as package maintainer want to use this, you should
                  probably think about setting this variable somewhere
                  in an Xresources file.
                  
     
     Functions:
       Anything matching [a-z,A-Z,_] is taken as a function (and an error
       is generated if the function doesn't exist). The arguments of the
       functions can be other functions, string constants or variables.
       
       prefix()
          returns the current prefix dir: either $rootprefix, or
          $HOME/$userprefix, depending on who runs install-menu
     
       ifroot($rootarg, $userarg)
          if(getuid()==0) print $rootarg, else print $userarg
     
       print($arg)    
          Same as just $arg; if $arg is empty, generate an error.
     
       nstring($n, $string)
          write $string $n times. So, nstring(3,"Aa") writes "AaAaAa".
          (Useful in combination with level()).
     
       esc($arg1,$arg2)
          Print $arg1, but escape all occurrences of characters in $arg2
          with a \. (thus, if arg1="hello", arg2="lo", print "he\l\l\o").
     
       escwith($arg1, $arg2, $arg3)
          Same as esc, but use $arg3 as escape sequence.
     
       escfirst($arg1, $arg2, $arg3)
          Same as escwith, but only escapes thirst occurrence of $arg2.
     
       cppesc($arg1)
          Escape anything that isn't a letter, number or _ with
          $<hex-ascii-code>. So, for example, a '-' is replaced by '$2D'.
          This way, $arg1 can be used as a #define in cpp.
     
       tolower($arg)
       toupper($arg)
          Returns the argument set in lowercases resp uppercases. 
     
       replacewith($s, $replace, $with)
          Search s for occurrences of characters from string replace, and
          replace them by the corresponding character in $with.
          Example:
           replacewith_string("hello $world, %dir", "$% ", "123")
           returns:   "hello31world,32dir"
     
       ifempty($arg1, $arg2)
          If $arg1 is empty, print $arg2, otherwise print nothing.
          For compatibility, $arg1="none" is interpreted as empty.
     
       ifnempty($arg1, $arg2)     
          If $arg1 is not empty, print $arg2.
          For compatibility, the string "none" is seen as empty.
     
       ifelse($arg1,$arg2,$arg3)
          If $arg1 is non-empty, print $arg2, otherwise $arg3.
          For compatibility, the string "none" is seen as empty.
     
       ifeq($arg1, $arg2, $arg3)
          If ($arg1==$arg2) then print $arg3
       ifneq($arg1, $arg2, $arg3)
          If ($arg1!=$arg2) then print $arg3
       ifeqelse($arg1, $arg2, $arg3, $arg4)
          If ($arg1==$arg2) then print $arg3 else print $arg4
     
       cond_surr($arg1, $arg2, $arg3)
          If $arg1 is non-empty print $arg2$arg1$arg3, otherwise print nothing.
          For compatibility, $arg1="none" is interpreted as empty.
     
       iffile($arg1, $arg2)
          If file $arg1 exists, and can be opened for reading by whoever
          started the current process, return $arg2, otherwise return nothing.
     
     
       ifelsefile($arg1, $arg2, $arg3)
          If file $arg1 exists, and can be opened for reading by whoever
          started the current process, return $arg2, otherwise return $arg3.
     
       catfile($arg1)
          Return the contents of file $arg1.
       
       forall($array, "var", $exec)
          For each element of the column separated array $array, set
          $var to that element, and print $exec.
          Example:
           forall("eo:nl", "lang", " name[" $lang "]=\"" translate($lang, title()) "\"\n")
          will print:
           name[eo]="Mi estas titolo"
           name[nl]="Ik ben een titel"
     
       parent($arg)
          for $arg a "directory", return parent directory:
          parent("/Debian/Apps/Editors") = "/Debian/Apps".
     
       basename($arg)
          return the last part of the parent directory:
          basename("/Debian/Apps/Editors") = "Apps".
     
       stripdir($arg)
          everything after the last slash, i.e. what basename() 
          should have returned: stripdir("/Debian/Apps/Editors") = "Editors".
     
       entrycount()
          the number of entries in this menu.
      
       entryindex()
          returns relative position of this entry. Start with 0,
          last entry is entrycount() - 1.
          BUG: if sort= anything other than $title, then this
          entryindex() will return incorrect values.
     
       firstentry($arg)
          return $arg if this is the first entry of this menu
          (that is, entryindex() = 0). Else, return nothing.
     
       lastentry()
          return $arg if this is the last entry in this menu
          (that is, entryindex() = entrycount() -1). Else, return nothing.
          
       level()
          return nesting of this menu in the total menu tree.
     
       add($arg1,$arg2)
       sub($arg1,$arg2)
       mult($arg1,$arg2)
       div($arg1,$arg2)
          returns the sum, difference, product or quotient of $arg1 and
          $arg2. Note that the arguments are strings, that are converted
          to integers.
          example: mult("24", entryindex())
          
       rcfile() examplercfile()  mainmenutitle() rootsection() rootprefix() 
       userprefix() treewalk() postoutput() preoutput()
          These functions all output whatever they were defined to be in
          the menu-method file.
     
       translate($lang, $text)
          translate $text into $lang.
          example:
            translate("eo", "Apps")
          prints:
            Aplikoj
     
     String constants, variables and functions can be concatenated 
     by placing them after each other with a space in between, like:
     
     "hello" ifelse($comma, $comma, " sorry" $period " comma not defined") " world"