use strict;
my $str = 'begin [(Mary [(had [(a )]lil\' [(lamb [(whose [(fleece )])])])])]was [(white [( as )])]snow
1 2 3 3 3 4 5 5 4 3 2 1 1 2 2 1
begin [(Mary [(had lil\' [(lamb [(whose )])])])]was [(white )]snow
1 2 3 4 4 3 2 1 1 1
begin [(Mary [(had lil\' [(lamb )])])]was snow
1 2 3 3 2 1
begin [(Mary [(had lil\' )])]was snow
1 2 2 1
begin [(Mary )]was snow
1 1
begin was snow
begin was snow
';
my $regex = qr/\[\((?:(?!\[\().)*?\)\]/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