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_posts/2014-07-17-writting-own-completions-p2.md

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+---
+category: en
+type: paper
+hastr: true
+layout: paper
+tags: linux, development
+title: Writting own Shell completions. Bash
+short: writting-own-completions-p2
+---
+<figure class="img">![bash_completion](/resources/papers/bash_completion.png)</figure> Some basics of creating a completion files for own application are described in these articles.
+
+<!--more-->
+
+## <a href="#preamble" class="anchor" id="preamble"><span class="octicon octicon-link"></span></a>Preamble
+
+While developing [one of my projects](/ru/projects/netctl-gui "Netctl-gui project page") 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.
+
+## <a href="#introduction" class="anchor" id="introduction"><span class="octicon octicon-link"></span></a>Introduction
+
+Bash, [unlike zsh](/ru/2014/07/17/writting-own-completions-p1 "Zsh completions paper"), 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 `pacman` completion files in my system.
+
+Lets consider the example of the same my application. I remind you that a part of help message is as follows:
+
+```bash
+netctl-gui [ -h | --help ] [ -e ESSID | --essid ESSID ] [ -с FILE | --config FILE ]
+           [ -o PROFILE | --open PROFILE ] [ -t NUM | --tab NUM ] [ --set-opts OPTIONS ]
+```
+
+Here is a flag list:
+* flags `-h` and `--help` do not require any arguments;
+* flags `-e` and `--essid` require a string argument without completion;
+* flags `-c` and `--config` require a string argument, which is a file;
+* flags `-o` and `--open` require a string argument, there is a completion from files in the specified directory;
+* flags `-t` and `--tab` require a string argument, there is a completion from the specified array;
+* flag `--set-opts` requires a string argument, there is a completion from the specified array comma separated;
+
+## <a href="#file" class="anchor" id="file"><span class="octicon octicon-link"></span></a>The file pattern
+
+Here **all** 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 `_netctl_profiles()` should be generated each time:
+
+```bash
+# variables
+_netctl_gui_arglist=()
+_netctl_gui_settings=()
+_netctl_gui_tabs=()
+_netctl_profiles() {}
+```
+
+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:
+
+```bash
+# work block
+_netctl-gui() {}
+```
+
+And finally again **without isolation in a separate function** we create a dependence "function-application":
+
+```bash
+complete -F _netctl_gui netctl-gui
+```
+
+## <a href="#flags" class="anchor" id="flags"><span class="octicon octicon-link"></span></a>Flags
+
+As it was said above there is no specific format, so all available flags declare by array:
+
+```bash
+_netctl_gui_arglist=(
+    '-h'
+    '--help'
+    '-e'
+    '--essid'
+    '-c'
+    '--config'
+    '-o'
+    '--open'
+    '-t'
+    '--tab'
+    '--set-opts'
+)
+```
+
+## <a href="#variables" class="anchor" id="variables"><span class="octicon octicon-link"></span></a>Arrays of variables
+
+I just give a function that looked like this in zsh:
+
+```bash
+_netctl_profiles() {
+    print $(find /etc/netctl -maxdepth 1 -type f -printf "%f\n")
+}
+```
+
+Bash does not allow to do so, so this function should be a little changed:
+
+```bash
+_netctl_profiles() {
+    echo $(find /etc/netctl -maxdepth 1 -type f -printf "%f\n")
+}
+```
+
+## <a href="#body" class="anchor" id="body"><span class="octicon octicon-link"></span></a>Function
+
+The variable `COMPREPLY` responds for completion in Bash. To keep track of the current state function `_get_comp_words_by_ref` must be called with parameters `cur` (current flag) and `prev` (previous flag, it is the state). Also some point for case are needed (variables `want*`). Function `compgen` is used for completion generation. A list of words is given after flag `-W`. (Also there is flag `-F` 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.
+
+So, here is our function:
+
+```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
+}
+```
+
+## <a href="#conclusion" class="anchor" id="conclusion"><span class="octicon octicon-link"></span></a>Conclusion
+
+File should be places to `/usr/share/bash-completion/completions/` with any name. You may found the example [in my repository](//raw.githubusercontent.com/arcan1s/netctl-gui/master/sources/gui/bash-completions "File").