Linux – Smart tab completion (for directories)

As of bash 4.2, this behavior is governed by

shopt -s direxpand # enable
shopt -u direxpand # disable

See http://www.mail-archive.com/bug-bash@gnu.org/msg11251.html for background information.

If you look at the function _cd() in /etc/bash_completion, you'll see that it appends the trailing slash itself and that complete gets called with the option -o nospace for cd.

You can do the same for xyz, but to have to verify separately if the found match is a directory (if so, append slash) or a file (if so, append space). This should be done in a for loop to process all found matches.

Also, to properly handle paths that contain spaces, you have to set the internal file separator to only newline and escape the spaces. Using IFS=$'\n' in combination with printf %q makes completion work with almost all characters.¹ Special care has to be taken to not escape the trailing space.

The following should work:

_xyz ()
{
    local IFS=$'\n'
    local LASTCHAR=' '

    COMPREPLY=($(compgen -o plusdirs -f -X '!*.txt' \
        -- "${COMP_WORDS[COMP_CWORD]}"))

    if [ ${#COMPREPLY[@]} = 1 ]; then
        [ -d "$COMPREPLY" ] && LASTCHAR=/
        COMPREPLY=$(printf %q%s "$COMPREPLY" "$LASTCHAR")
    else
        for ((i=0; i < ${#COMPREPLY[@]}; i++)); do
            [ -d "${COMPREPLY[$i]}" ] && COMPREPLY[$i]=${COMPREPLY[$i]}/
        done
    fi

    return 0
}

complete -o nospace -F _xyz xyz

_{¹ The newline character is the obvious exception here, since it is an internal file separator.}