Accessing bash completions for specific commands programmatically

Question

I'm trying to write a small command launcher application, and would like to use bash's tab completions in my own completion system. I've been able to get a list of completions for general commands using compgen -abck.
However, I would also like to get completions for specific commands: for instance, the input git p should display completion for git's commands.

Is there any way I can use compgen to do this? If not, are there any other ways I can get a list of completions programmatically?

[EDIT: To clarify, I'm not trying to provide completion to bash - my app is a GUI command launcher. I'd simply like to use bash's existing completions in my own app.]

Answer 1

I don't really know how it works, but the awesome window manager uses the following Lua code for getting access to bash completion's result:

https://github.com/awesomeWM/awesome/blob/master/lib/awful/completion.lua#L119

1. Via complete -p we find complete -o bashdefault -o default -o nospace -F _git git. We remember "_git" for later.
2. The length of "git l" is 5, so we set COMP_COUNT=6. We are completing the first argument to "git", so COMP_CWORD=1.

All together we use the following script:

__print_completions() {
    printf '%s\n' "${COMPREPLY[@]}"
}

# load bash-completion functions
source /etc/bash_completion

# load git's completion function
_completion_loader git

COMP_WORDS=(git l)
COMP_LINE='git l'
COMP_POINT=6
COMP_CWORD=1
_git
__print_completions

Output: "log"

Answer 2

Take a look at the Debian Administration An introduction to bash completion - it's fairly easy to understand - by the way, it also has a part two.

Answer 3

Check in the /etc/bash_completion.d/ directory. This is where the different command completion scripts stay.

Answer 4

Here a simple but working example in bash :

function foo_completion()
{
    local currentWord=${COMP_WORDS[COMP_CWORD]}
    local completionList=""

    case "${COMP_CWORD}" in
        "1")
            completionList="command1 command2 command3";
            ;;
        "2")
            completionList="param1 param2 param3";
            ;;
    esac

    COMPREPLY=( $( compgen -W "${completionList}" -- ${currentWord} ) )
}

complete -F foo_completion foo

With this kind of code, you will get commandN completed when you type "foo c" + tab and paramN completed when you type "foo command1 p" + tab

You can compute the completion list from the command help.

my2c

Answer 5

I hacked up this script a while back which gives you pretty accurate Man-page Bash Completion I know other people have done similar things with parsing --help option output.