bash autocompletion: add description for possible completions

Question

Is it possible to make bash auto-completion look like in Cisco IOS shell?

I mean to add short descriptions for each completion, like this:

telnet 10.10.10. (TAB Pressed)
 10.10.10.10 - routerA
 10.10.10.11 - routerB

where 10.10.10.10 and 10.10.10.11 are possible completions and routerA & routerB just descriptions (not to be executed).

I know that bash can complete commands with "complete -W", but is it able to print descriptions for them?

Answer 1

I have a solution to this that does not require pressing TAB more than twice or echoing any extra information. The key is to check whether there is only one completion, then strip that completion down to the valid portion, usually by removing the largest matching suffix after your "comment" delimiter. To accomplish the OP's example:

_telnet() {
  COMPREPLY=()
  local cur
  cur=$(_get_cword)
  local completions="10.10.10.10 - routerA
10.10.10.11 - routerB
10.20.1.3 - routerC"

  local OLDIFS="$IFS"
  local IFS=$'\n'
  COMPREPLY=( $( compgen -W "$completions" -- "$cur" ) )
  IFS="$OLDIFS"
  if [[ ${#COMPREPLY[*]} -eq 1 ]]; then #Only one completion
    COMPREPLY=( ${COMPREPLY[0]%% - *} ) #Remove ' - ' and everything after
  fi
  return 0
}
complete -F _telnet -A hostnames telnet

This gives the exact output you're looking for, and when there is only one possible completion, the comment is stripped from it before completing.

Answer 2

I'd use conversion based on whether the number of candidates become one (as shown by @bonsaiviking) for simple cases and the following if I needed more flexibility in what I want to show the user.

__foo () {
    local WORDS
    WORDS=("1|10.10.10.10|routerA" "2|10.10.10.11|routerB")

    local FOR_DISPLAY=1
    if [ "${__FOO_PREV_LINE:-}" != "$COMP_LINE" ] ||
            [ "${__FOO_PREV_POINT:-}" != "$COMP_POINT" ]; then
        __FOO_PREV_LINE=$COMP_LINE
        __FOO_PREV_POINT=$COMP_POINT
        FOR_DISPLAY=
    fi

    local IFS=$'\n'
    COMPREPLY=($(
        for WORD in "${WORDS[@]}"; do
            IFS=\| read -ra SP <<<"$WORD"
            if [ "${SP[1]:0:${#2}}" == "$2" ]; then
                if [ -n "$FOR_DISPLAY" ]; then
                    printf "%-*s\n" "$COLUMNS" "${SP[0]}: ${SP[1]} - ${SP[2]}"
                else
                    echo "${SP[1]}"
                fi
            fi
        done
    ))
}
complete -F __foo x

Note: You could probably use COMP_TYPE to set FOR_DISPLAY in Bash 4.x but I needed to support Bash 3.x as well.

This behaves as follows:

$ x 1

Tab

$ x 10.10.10.1

TabTab

1: 10.10.10.10 - routerA
2: 10.10.10.11 - routerB
$ x 10.10.10.1