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

In Perl, you can use Marpa, a general BNF parser — the parser code is in this gist.

BNF parser is arguably more maintainable than a regex. Parens around grammar symbols hide their values from the parse tree thus simplifying the post-processing.

Hope this helps.

Answer 2

Perlishly I'd do:

my @all_keys; 

while ( <DATA> ) {
   push ( @all_keys, m/\((.+?)\)/g  );
}
print join ("\n",@all_keys);


__DATA__
dummy
(key1)
(key2)dummy(key3)
dummy(key4)dummy
dummy(key5)dummy))))dummy
dummy(key6)dummy))(key7)dummy))))

This assumes that 'keys' match the \w in perlre (alphanumeric plus "_",)

(If you're not familiar with perl, you can pretty much just swap that <DATA> for <STDIN> and pipe the data straight to your script - or do more interesting things with @all_keys)

Answer 3

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