use strict;
my $str = 'some random texts (100+ lines)
bbb
...
ttt
some random texts
ccc
...
fff
paragraph_a A_story(
...
some random texts adfsasdsd
...
)
paragraph_a A_story(
...
some random texts adfsasdsd
...
)
paragraph_a A_story(
...
some random texts adfsasdsd
...
)
paragraph_b different_story(
...
some random texts
...
)
paragraph_b different_story(
...
some random texts
...
)';
my $regex = qr/^(?!paragraph_b)\w+ \w+\((?:\n(?!^\w+ \w+\().*)*\)(?=\s*^paragraph_b)/mp;
my $subst = '';
my $result = $str =~ s/$regex/$subst/rg;
print "The result of the substitution is' $result\n";
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for Perl, please visit: http://perldoc.perl.org/perlre.html