use strict;
my $str = 'First string
Second string [Ignore This Part]
Third string (1) [Ignore This Part]
[Ignore This Part]';
my $regex = qr/(?<=\S)[^\S\n]*\[[^][\n]*]$/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