Regular Expression to find a string included between two characters while EXCLUDING the delimiters

Question

I need to extract from a string a set of characters which are included between two delimiters, without returning the delimiters themselves.

A simple example should b

Answer 1

I had the same problem using regex with bash scripting. I used a 2-step solution using pipes with grep -o applying

 '\[(.*?)\]'  

first, then

'\b.*\b'

Obviously not as efficient at the other answers, but an alternative.