use Benchmark;
 
undef $/;
open DATA, "/home/jeroen/texs/review/reviewnew.tex" or die $!; #just some lengthy manuscript
$str = <DATA>;
open DUMP, ">/dev/null";
 
timethese( -1, {'regex' =>
  sub {
   $a = $str;
   print DUMP map "$_\n", $a=~/\G(.{1,80})/gs;
  },
           'substr' =>
  sub {
    $a = $str; $b='';
    $b .= substr( $a, 0, 80, '')."\n" while length($a) >80;
    print DUMP "$b$a";
  }
});

#givesBenchmark: running regex, substr, each for at least 1 CPU seconds...
     regex:  1 wallclock secs ( 1.05 usr +  0.01 sys =  1.06 CPU) @ 287.74/s (n=305)
    substr:  1 wallclock secs ( 1.26 usr +  0.01 sys =  1.27 CPU) @ 556.69/s (n=707)

#This changes a bit when leaving the map out:

Benchmark: running regex, substr, each for at least 1 CPU seconds...
     regex:  2 wallclock secs ( 1.06 usr +  0.00 sys =  1.06 CPU) @ 396.23/s (n=420)
    substr:  2 wallclock secs ( 1.04 usr +  0.02 sys =  1.06 CPU) @ 547.17/s (n=580)

#I left the print out@substr at first (didn't want to test
# print), but putting it back in gives:

Benchmark: running regex, substr, each for at least 1 CPU seconds...
     regex:  1 wallclock secs ( 1.30 usr +  0.01 sys =  1.31 CPU) @ 366.41/s (n=480)
    substr:  1 wallclock secs ( 1.06 usr +  0.02 sys =  1.08 CPU) @ 473.15/s (n=511)

#I added a better comparison:
        Rate regmap  regex fixreg substr
regmap 285/s     --   -19%   -22%   -56%
regex  350/s    23%     --    -4%   -46%
fixreg 364/s    28%     4%     --   -44%
substr 650/s   128%    86%    78%     --