Matching optional parameters with non-capturing groups in Bash regular expression

Question

I want to parse strings similar to the following into separate variables using regular expressions from within Bash:

Category: entity;scheme=\"http://schemas         


        

Answer 1

You can emulate non-matching groups in bash using a little bit of regexp magic:

              _2__    _4__   _5__
[[ "fu@k" =~ ((.+)@|)((.+)/|)(.+) ]];
echo "${BASH_REMATCH[2]:--} ${BASH_REMATCH[4]:--} ${BASH_REMATCH[5]:--}"
# Output: fu - k

Characters @ and / are parts of string we parse. Regexp pipe | is used for either left or right (empty) part matching.

For curious, ${VAR:-} is variable expansion with default value in case $VAR is empty.