pl@nereida:~/Lperltesting$ cat comparequotedstrings.pl
#!/usr/local/lib/perl/5.10.1/bin//perl5.10.1
use v5.10;
use Benchmark qw{cmpthese};

# See http://www.regex-engineer.org/slides/img10.html
my $regexp = qr/
    "             # double quote
    (?:           # no memory
        [^"\\]++  # no " or escape: Don't backtrack
    | (?: \\.)++  # escaped character
  )*+             # Don't backtrack
    "             # end double quote
/x;

my $bregexp = qr/
  "               # double quote
  (?:             # no memory
      [^"\\]+     # no " or escape: backtrack
    | (?: \\.)+   # escaped character
  )*              # backtrack
  "             # end double quote
/x;

# input matches many times. Using "g" option
my $input = (q{"abc\"defg"hijk}x10000);
cmpthese( 0,
  {
    gbacktrack => q{ $input =~ /$bregexp/g },
    gpossessive  => q{ $input =~ /$regexp/g }
  }
);

#input matches a long string, no g option
$input = '"'.(q{abc\"defg}x10000).'"';
cmpthese( 0,
  {
    backtrack => q{ $input =~ /$bregexp/ },
    possessive  => q{ $input =~ /$regexp/ }
  }
);
# input does not match. Using "g" option
$input = '"'.("abcdefghijk"x10000);
cmpthese( 0,
  {
    failgbacktrack => q{ $input =~ /$bregexp/g },
    failgpossessive  => q{ $input =~ /$regexp/g }
  }
);