Showing only the substrings of COMPREPLY bash completion options to the user

Question

In a bash completion script, suppose COMPREPLY=(aa/ba/ aa/bb/). When the script is invoked, the completion options looks like this to the user:

$ foo aa/b<TAB>
aa/ba/
aa/bb/

However, I want to have a bit more control over how these options are displayed. In particular, I want to show only a substring of each COMPREPLY option to the user, similar to how directory completion works in bash now:

$ foo aa/b<TAB>
ba/
bb/

Is there any way of doing this in bash?

Answer 1

This piece of code taken from debian sid /etc/bash_completion should help:

# Remove colon-word prefix from COMPREPLY items
local colon_word=${1%${1##*:}}
local i=${#COMPREPLY[*]}
while [ $((--i)) -ge 0 ]; do
    COMPREPLY[$i]=${COMPREPLY[$i]#"$colon_word"}
done