use warnings;
use strict;
use Test::More;

# in Ruby: (?~abc)
my $re1 = qr{ \A (?: (?!abc) . )* \z }x;
like '', $re1;
like 'ab', $re1;
like 'aab', $re1;
like 'ccdd', $re1;
unlike 'abc', $re1;
unlike 'aabc', $re1;
unlike 'ccccabc', $re1;
unlike 'ccabcdd', $re1;

# in Ruby: (?~abc)c
# this example fails in Perl
like 'abc', qr{ \A (?: (?!abc) . )* c \z }x;

# in Ruby: \A\/\*(?~\*\/)\*\/\z
my $re2 = qr{ \A /\* ( (?!\*/). )*? \*/ \z }x;
like '/**/', $re2;
like '/* foobar */', $re2;
unlike '/**/ */', $re2;

done_testing;