How to enable default file completion in bash

Question

Say I have a command named \"foo\" that takes one argument (either \"encrypt\" or \"decrypt\") and then a list of files. I want to write a bash completion script that helps wit

Answer 1

The bash documentation can be a little enigmatic. The simplest solution is to alter the completion function binding:

complete -o filenames -F _foo foo

This means the function returns filenames (including directories), and special handling of the results is enabled.

(IMHO the documentation doesn't make it clear that this effectively post-processes COMPREPLY[] as set by your completion function; and that some of the -o options, that one included, when applied to compgen appear to have no effect.)

You can get closer to normal bash behaviour by using:

 complete -o filenames -o bashdefault -F _foo foo

that gets you "~" completion back.

There are two problems with the above however:

• if you have a directory named "encrypt" or "decrypt" then the expansion of your keywords will grow a trailing "/"
• $VARIABLE expansion won't work, $ will become \$ to better match a filename with a $. Similarly @host expansion won't work.

The only way that I have found to deal with this is to process the compgen output, and not rely on the "filenames" post-processing:

_foo()
{
    local cmds cur ff
    if (($COMP_CWORD == 1))
    then
        cur="${COMP_WORDS[1]}"
        cmds="encrypt decrypt"
        COMPREPLY=($(compgen -W "$cmds" -- "$cur"))
        COMPREPLY=( "${COMPREPLY[@]/%/ }" )   # add trailing space to each
    else
        # get all matching files and directories
        COMPREPLY=($(compgen -f  -- "${COMP_WORDS[$COMP_CWORD]}"))

        for ((ff=0; ff<${#COMPREPLY[@]}; ff++)); do
            [[ -d ${COMPREPLY[$ff]} ]] && COMPREPLY[$ff]+='/'
            [[ -f ${COMPREPLY[$ff]} ]] && COMPREPLY[$ff]+=' '
        done
    fi
}

complete -o bashdefault -o default -o nospace -F _foo foo

(I also removed the superfluous array for cmd in the above, and made compgen more robust and handle spaces or leading dashes in filenames.)

The downsides now are that when you get the intermediate completion list (i.e. when you hit tab twice to show multiple matches) you won't see a trailing / on directories, and since nospace is enabled the ~ $ @ expansions won't grow a space to cause them to be accepted.

In short, I do not believe you can trivially mix-and-match your own completion and the full bash completion behaviour.