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<?xml version="1.0"?>
<guide self="tasks-reference/completion/">
<chapter>
<title>Completion Files</title>
<body>

<p>
Since v2.05a, <c>bash</c> has offered intelligent programmable completion.  Writing
such completions for your own programs/things you maintain is relatively easy
provided you know bash already. See `bash-completion.eclass Reference`_ for how
to install completion files.
</p>

<section>
<title>Completion-Related Internal Bash Variables</title>
<body>

<p>
Most of these variables lose their special properties when unset, even if they
are subsequently reset.
</p>

<table>
  <tr>
    <th>
      Variable
    </th>
    <th>
      Purpose
    </th>
  </tr>
  <tr>
    <ti>
      <c>COMP_CWORD</c>
    </ti>
    <ti>
      An index into <c>${COMP_WORDS}</c> of the word containing the
      current cursor position.
    </ti>
  </tr>
  <tr>
    <ti>
      <c>COMP_LINE</c>
    </ti>
    <ti>
      The current command line.
    </ti>
  </tr>
  <tr>
    <ti>
      <c>COMP_POINT</c>
    </ti>
    <ti>
      The index of the current cursor position relative to the
      beginning of the current command.  If the current cursor
      position is at the end of the current command, the value
      of this variable is equal to <c>${#COMP_LINE}</c>.
    </ti>
  </tr>
  <tr>
    <ti>
      <c>COMP_WORDBREAKS</c>
    </ti>
    <ti>
      The set of characters that the Readline library treats as
      word separators when performing word completion.
    </ti>
  </tr>
  <tr>
    <ti>
      <c>COMP_WORDS</c>
    </ti>
    <ti>
      An array variable consisting of the individual words in
      the current command line, <c>${COMP_LINE}</c>.
    </ti>
  </tr>
  <tr>
    <ti>
      <c>COMPREPLY</c>
    </ti>
    <ti>
      An array variable from which bash reads the possible
      completions generated by a completion function.
    </ti>
  </tr>
</table>

</body>
</section>

<section>
<title>Completion-Related Bash Builtins</title>
<body>

<p>
See `bash-1`_ for a full description of these builtins and their options.
</p>

<table>
  <tr>
    <th>
      Builtin
    </th>
    <th>
      Usage
    </th>
  </tr>
  <tr>
    <ti>
      <c>compgen</c>
    </ti>
    <ti>
      <c>compgen [-abcdefgjksuv] [-o option] [-A action] [-G globpat]
      [-W wordlist] [-P prefix] [-S suffix] [-X filterpat]
      [-F function] [-C command] [word]</c>
      Display the possible completions depending on the options.
      Intended to be used from within a shell function generating
      possible completions. If the optional WORD argument is supplied,
      matches against WORD are generated.
    </ti>
  </tr>
  <tr>
    <ti>
      <c>complete</c>
    </ti>
    <ti>
      <c>complete [-abcdefgjksuv] [-pr] [-o option] [-A action]
      [-G globpat] [-W wordlist] [-P prefix] [-S suffix]
      [-X filterpat] [-F function] [-C command] [name ...]</c>
      For each NAME, specify how arguments are to be completed.
      If the -p option is supplied, or if no options are supplied,
      existing completion specifications are printed in a way that
      allows them to be reused as input.  The -r option removes a
      completion specification for each NAME, or, if no NAMEs are
      supplied, all completion specifications.
    </ti>
  </tr>
</table>

<p>
For extremely simple cases, a simple <c>complete</c> statement is all that is
needed.  For example, minimal <c>cd</c> completion (minimal as in no support for
<c>${CDPATH}</c>) would be as simple as:
</p>

<codesample lang="ebuild">
complete -o nospace -d cd
</codesample>

</body>
</section>

<section>
<title>Anatomy of a Completion Function</title>
<body>

<p>
Nearly all completion functions will start out the same way. For these cases,
the following can be used as a template for creating new completion functions:
</p>

<codesample lang="ebuild" numbering="lines">
_foo() {
    local cur prev opts
    COMPREPLY=()
    cur="${COMP_WORDS[COMP_CWORD]}"
    prev="${COMP_WORDS[COMP_CWORD-1]}"
    opts=""

    if [[ ${cur} == -* || ${COMP_CWORD} -eq 1 ]] ; then
        COMPREPLY=( $(compgen -W "${opts}" -- ${cur}) )
        return 0
    fi

    case "${prev}" in
      # ...
    esac
}
complete -F _foo foo
</codesample>

<table>
  <tr>
    <th>
      Line
    </th>
    <th>
      Explanation
    </th>
  </tr>
  <tr>
    <ti>
      1
    </ti>
    <ti>
      The convention for completion function names is usually _NAME, where NAME
      is the name of the application/function you are writing the completion
      function for.  If NAME contains a '-', it should be replaced with a '_'.
      Hence bash-completion-config would be _bash_completion_config().  Failing
      to do so can cause weird bugs if bash is invoked in POSIX-mode while a
      function name containing a '-' is in the environment (POSIX sh does not
      allow a '-' in function names).
    </ti>
  </tr>
  <tr>
    <ti>
      3
    </ti>
    <ti>
      Resets the <c>${COMPREPLY}</c> array, as it may be set from a previous
      invocation.
    </ti>
  </tr>
  <tr>
    <ti>
      4
    </ti>
    <ti>
      Sets the local variable, <c>${cur}</c> to the current word of the command line.
      If the current command line, <c>${COMP_LINE}</c> is say 'foo --fil', <c>${cur}</c>
      would be equal to '--fil'.  If <c>${COMP_LINE}</c> is equal to 'foo --file '
      (note the space at the end), <c>${cur}</c> is null.
    </ti>
  </tr>
  <tr>
    <ti>
      5
    </ti>
    <ti>
      Sets the local variable, <c>${prev}</c> to the previous word of the command
      line.  <c>${prev}</c> is the word before <c>${cur}</c>.
    </ti>
  </tr>
  <tr>
    <ti>
      6
    </ti>
    <ti>
      Sets the local variable, <c>${opts}</c>.  In a real completion function, this
      variable would be set to all the options that <c>foo</c> recognizes.
    </ti>
  </tr>
  <tr>
    <ti>
      8
    </ti>
    <ti>
      Tests whether or not the current word is equivalent to -* (an option) or if
      we're completing on the first word (ie. <c>${COMP_CWORD}</c> == 1).
    </ti>
  </tr>
  <tr>
    <ti>
      9
    </ti>
    <ti>
      If the test returns true, show the available options, <c>${opts}</c>. The -W
      option to <c>compgen</c> tells bash to complete on the word list (string or
      something that evaluates to a string).  In the majority of cases, you'll
      pass <c>'-- ${cur}'</c> to <c>compgen</c> telling it to only return those
      completions that match <c>${cur}</c>.
    </ti>
  </tr>
  <tr>
    <ti>
      13
    </ti>
    <ti>
      Most of the time, you'll want to perform a certain action if <c>${prev}</c> is
      equal to a certain option.  For example, if <c>foo</c> has a --file option
      (and -f for short) that takes any kind file, you could do:
      <codesample lang="ebuild">
case "${prev}" in
    -f|--file)
        COMPREPLY=( $(compgen -f ? ${cur}) )
        ;;
esac</codesample>
    </ti>
  </tr>
  <tr>
    <ti>
      17
    </ti>
    <ti>
      Tells bash to use the <c>_foo</c> function to generate any completions for
      the <c>foo</c> application/function.
    </ti>
  </tr>
</table>

</body>
</section>

<section>
<title>Real-World Example</title>
<body>

<p>
For this document, I will take you through a real-world example and write a
real completion function for <c>revdep-rebuild</c> (might even be available in
<c>gentoo-bashcomp</c> by the time you read this :]).
</p>

<codesample lang="ebuild" numbering="lines">
_revdep_rebuild() {
	local cur prev opts
	COMPREPLY=()
	cur="${COMP_WORDS[COMP_CWORD]}"
	prev="${COMP_WORDS[COMP_CWORD-1]}"
	opts="-X --package-names --soname --soname-regexp -q --quiet"

	if [[ ${cur} == -* || ${COMP_CWORD} -eq 1 ]] || \
	   [[ ${prev} == @(-q|--quiet) ]] ; then
		COMPREPLY=( $(compgen -W "${opts}" -- ${cur}) )
		return 0
	fi
 
	case "${prev}" in
		-X|--package-names)
			_pkgname -I ${cur}
			;;
		--soname)
			local sonames=$(for x in /lib/*.so?(.)* /usr/lib*/*.so\?(.)* ; do \
						echo ${x##*/} ; \
						done)
			COMPREPLY=( $(compgen -W "${sonames}" -- ${cur}) )
			;;
		--soname-regexp)
			COMPREPLY=()
			;;
		*)
			if [[ ${COMP_LINE} == *" "@(-X|--package-names)* ]] ; then
				_pkgname -I ${cur}
				COMPREPLY=(${COMPREPLY[@]} $(compgen -W "${opts}"))
			else
				COMPREPLY=($(compgen -W "${opts} -- ${cur}"))
			fi
		;;
	esac
}
complete -F _revdep_rebuild revdep-rebuild
</codesample>

<p>
Lines 1-12 are pretty much the same as in the previous section.
</p>

<table>
  <tr>
    <th>
      Line
    </th>
    <th>
      Explanation
    </th>
  </tr>
  <tr>
    <ti>
      15
    </ti>
    <ti>
      If <c>${prev}</c> is equal to <c>-X</c>
      or <c>--package-names</c>, call <c>_pkgname</c> (a function
      defined by <c>gentoo-bashcomp</c> that completes on package
      names - it sets <c>${COMPREPLY}</c>, so we don't worry about
      that here).
    </ti>
  </tr>
  <tr>
    <ti>
      18
    </ti>
    <ti>
      If <c>${prev}</c> is equal to <c>--soname</c>, generate a list
      of all shared libs in <c>/lib</c> and <c>/usr/lib*</c>. Pass
      that list to <c>compgen</c> to generate a list of possible
      completions that match <c>${cur}</c>.
    </ti>
  </tr>
  <tr>
    <ti>
      24
    </ti>
    <ti>
      Obviously we cannot complete on any regexp's so if <c>${prev}</c> is equal
      to <c>--soname-regexp</c>, do nothing.
    </ti>
  </tr>
  <tr>
    <ti>
      27
    </ti>
    <ti>
      For anything else (any options not specified in the case statement above
      OR any argument to one of the options specified in the case statement)
      perform the tests. Since <c>--package-names</c> can take multiple package
      names, we want to continue to complete on package names until another
      recognized option is encountered (ie. is <c>${prev}</c>).
    </ti>
  </tr>
  <tr>
    <ti>
      30
    </ti>
    <ti>
      Since <c>_pkgname</c> sets <c>${COMPREPLY}</c> and we want to add to that list,
      we have to use the <c>COMPREPLY=(${COMPREPLY[@] ... )</c> construct.
    </ti>
  </tr>
  <tr>
    <ti>
      37
    </ti>
    <ti>
      Tell bash to use <c>_revdep_rebuild</c> to generate all possible completions
      for revdep-rebuild.
    </ti>
  </tr>
</table>

</body>
</section>

</body>
</chapter>
</guide>