---
category: en
type: paper
hasTr: true
layout: paper
tags: linux, development
title: Writting own Shell completions. Bash
short: writting-own-completions-p2
description: Some basics of creating a completion files for own application are described in these articles.
---
<h2><a name="preamble" class="anchor" href="#preamble"><span class="octicon octicon-link"></span></a>Preamble</h2>
<p>While developing <a href="/ru/projects/netctl-gui">one of my projects</a> I have wanted to add completion files. I have already tried to create these files, but I was too lazy to read some manuals about it.</p>

<h2><a name="introduction" class="anchor" href="#introduction"><span class="octicon octicon-link"></span></a>Introduction</h2>
<p>Bash, <a href="/ru/2014/07/17/writting-own-completions-p1">unlike zsh</a>, demands some dirty workarounds for completions. Cursory have Googled, I have not found a more or less normal tutorials, so it is based on the available <code>pacman</code> completion files in my system.</p>

<p>Lets consider the example of the same my application. I remind you that a part of help message is as follows:</p>

{% highlight bash %}
netctl-gui [ -h | --help ] [ -e ESSID | --essid ESSID ] [ -с FILE | --config FILE ]
           [ -o PROFILE | --open PROFILE ] [ -t NUM | --tab NUM ] [ --set-opts OPTIONS ]
{% endhighlight %}

<p>Here is a flag list:
<ul>
  <li>flags <code>-h</code> and <code>--help</code> do not require any arguments;</li>
  <li>flags <code>-e</code> and <code>--essid</code> require a string argument without completion;</li>
  <li>flags <code>-c</code> and <code>--config</code> require a string argument, which is a file;</li>
  <li>flags <code>-o</code> and <code>--open</code> require a string argument, there is a completion from files in the specified directory;</li>
  <li>flags <code>-t</code> and <code>--tab</code> require a string argument, there is a completion from the specified array;</li>
  <li>flag <code>--set-opts</code> requires a string argument, there is a completion from the specified array comma separated;</li>
</ul>
</p>

<h2><a name="file" class="anchor" href="#file"><span class="octicon octicon-link"></span></a>The file pattern</h2>
<p>Here <b>all</b> variables must return an array. And there no specific formats. First we declare the flags and then we describe all other variables. As I am not going to describe the functions in more detail below I remind you that <code>_netctl_profiles()</code> should be generated each time:

{% highlight bash %}
# variables
_netctl_gui_arglist=()
_netctl_gui_settings=()
_netctl_gui_tabs=()
_netctl_profiles() {}
{% endhighlight %}

Then there are main functions, which will be called for completion of specific application. In my case this there is only one applications, so there is only one function:

{% highlight bash %}
# work block
_netctl-gui() {}
{% endhighlight %}

And finally again <b>without isolation in a separate function</b> we create a dependence "function-application":

{% highlight bash %}
complete -F _netctl_gui netctl-gui
{% endhighlight %}
</p>

<h2><a name="flags" class="anchor" href="#flags"><span class="octicon octicon-link"></span></a>Flags</h2>
<p>As it was said above there is no specific format, so all available flags declare by array:

{% highlight bash %}
_netctl_gui_arglist=(
    '-h'
    '--help'
    '-e'
    '--essid'
    '-c'
    '--config'
    '-o'
    '--open'
    '-t'
    '--tab'
    '--set-opts'
)
{% endhighlight %}
</p>

<h2><a name="variables" class="anchor" href="#variables"><span class="octicon octicon-link"></span></a>Arrays of variables</h2>
<p>I just give a function that looked like this in zsh:

{% highlight bash %}
_netctl_profiles() {
    print $(find /etc/netctl -maxdepth 1 -type f -printf "%f\n")
}
{% endhighlight %}

Bash does not allow to do so, so this function should be a little changed:

{% highlight bash %}
_netctl_profiles() {
    echo $(find /etc/netctl -maxdepth 1 -type f -printf "%f\n")
}
{% endhighlight %}
</p>

<h2><a name="body" class="anchor" href="#body"><span class="octicon octicon-link"></span></a>Function</h2>
<p>The variable <code>COMPREPLY</code> responds for completion in Bash. To keep track of the current state function <code>_get_comp_words_by_ref</code> must be called with parameters <code>cur</code> (current flag) and <code>prev</code> (previous flag, it is the state). Also some point for case are needed (variables <code>want*</code>). Function <code>compgen</code> is used for completion generation. A list of words is given after flag <code>-W</code>. (Also there is flag <code>-F</code> which requires a function as argument, but it gives warning for me.) The last argument is a current string to which you want to generate completion.</p>

<p>So, here is our function:

{% highlight bash %}
_netctl_gui() {
    COMPREPLY=()
    wantfiles='-@(c|-config)'
    wantprofiles='-@(o|-open|s|-select)'
    wantsettings='-@(-set-opts)'

    wanttabs='-@(t|-tab)'
    _get_comp_words_by_ref cur prev

    if [[ $prev = $wantstring ]]; then
        # do not completion, wait for string
        COMPREPLY=()
    elif [[ $prev = $wantfiles ]]; then
        # completion from files in this directory
        _filedir
    elif [[ $prev = $wantprofiles ]]; then
        # completion from function
        COMPREPLY=($(compgen -W '${_netctl_profiles[@]}' -- "$cur"))
    elif [[ $prev = $wanttabs ]]; then
        # completion from array
        COMPREPLY=($(compgen -W '${_netctl_gui_tabs[@]}' -- "$cur"))
    elif [[ $prev = $wantsettings ]]; then
        # completion from array
        # flag -S add a comma after completion, but does not enable multi-selection =(
        COMPREPLY=($(compgen -S ',' -W '${_netctl_gui_settings[@]}' -- "$cur"))
    else
        # show all available flags
        COMPREPLY=($(compgen -W '${_netctl_gui_arglist[@]}' -- "$cur"))
    fi

    true
}
{% endhighlight %}
</p>

<h2><a name="conclusion" class="anchor" href="#conclusion"><span class="octicon octicon-link"></span></a>Conclusion</h2>
<p>File should be places to <code>/usr/share/bash-completion/completions/</code> with any name. You may found the example <a href="https://raw.githubusercontent.com/arcan1s/netctl-gui/master/sources/gui/bash-completions">in my repository</a>.</p>