use strict;
my $str = '-- test
# should be ""
--->>> test
# should be "--->>> test"
<<<--- test
# should be "<<<--- test"
--->>>->>> test
# should be --->>>->>> test
---->>> test
# should be ""
test --->>> test
# should be "test --->>> test"
test --->>> test <<<---
# should be "test --->>> test <<<---"
';
my $regex = qr/(?:(?<!-)--->>>|<<<---(?!-))(*SKIP)(*FAIL)|--.*/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