Extract string from brackets

Question

I\'m pretty new at bash so this is a pretty noob question..

Suppose I have a string:

string1 [string2] string3 string4

I would like

Answer 1

Another awk:

$ echo "string1 [string2] string3 [string4]" |
awk -v RS=[ -v FS=] 'NR>1{print $1}' 
string2
string4