Parsing of parenthesis with sed using regex

Question

I am looking for a command in sed which transforms this input stream:

dummy
(key1)
(key2)dummy(key3)
dummy(key4)dummy
dummy(key5)dummy))))dummy
         


        

Answer 1

You can use this lookbehind based regex in grep -oP:

grep -oP '(?<=\()[^)]+' file
key1
key2
key3
key4
key5
key6
key7

Or using awk:

awk -F '[()]' 'NF>1{for(i=2; i<=NF; i+=2) if ($i) print $i}' file
key1
key2
key3
key4
key5
key6
key7