Conditional trailing space with bash programmable completion - bash

Question

I'm creating a function to provide programmable completion for a command that I use (with much help from http://www.debian-administration.org/articles/317). The shell script usage is as follows:
script.sh command [command options]
where command can be either 'foo' or 'bar' and command options for 'foo' are 'a_foo=value' and 'b_foo=value' and command options for 'bar' are 'a_bar=value' and 'b_bar=value'.
Here's the configuration I'm using:
_script() {
local cur command all_commands
COMPREPLY=()
cur="${COMP_WORDS[COMP_CWORD]}"
command="${COMP_WORDS[1]}"
all_commands="foo bar"
case "${command}" in
foo)
COMPREPLY=( $(compgen -W "--a_foo --b_foo" -- ${cur}) ); return 0;;
bar)
COMPREPLY=( $(compgen -W "--a_bar --b_bar" -- ${cur}) ); return 0;;
*) ;;
esac
COMPREPLY=( $(compgen -W "${all_commands}" -- ${cur}) )
return 0
}
complete -F _script script.sh
This mostly works as I'd like:
% script.sh f[TAB]
completes to:
% script.sh foo
(with a trailing space as desired)
However, this:
% script.sh foo a[TAB]
completes to:
% script.sh foo a_foo
(also with a trailing space)
I'd like to replace the trailing space with an '='. Alternatively, I'd be willing to change the values passed to compgen to be "--a_foo= --b_foo=", in which case I could just delete the trailing space.
Unfortunately, the command is not under my control, so I can't change the command line options to be of format "--a_foo value" instead of "--a_foo=value".

Answer 1

First you need to add = to the COMPREPLY:
COMPREPLY=( $(compgen -W "--a_foo= --b_foo=" -- ${cur}) )
next you need to tell completion not to add space after = with
compopt -o nospace
So, you script lines should be:
foo)
COMPREPLY=( $(compgen -W "--a_foo= --b_foo=" -- ${cur}) ); compopt -o nospace; return 0;;
bar)
COMPREPLY=( $(compgen -W "--a_bar= --b_bar=" -- ${cur}) ); compopt -o nospace; return 0;;