Conditional trailing space with bash programmable completion

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".