use strict;                     # Purpose: In each benchmark invocation, have one
use warnings;                   # (constant) string copied to another- which is then 
                                # modified (shortened by the first character) and 
for my $n (1..4) {              # touched again (length determined and compared)
  use Benchmark qw(cmpthese);
  
  my $org_str = '|0' x 10**$n;  # generate the string in local scope
  my $mod_str = $org_str;       # do some allocation on the other string's PV
  print "string length: " . length($org_str) . "\n";
  
  cmpthese( -3,  {
     regexsubst => sub { # copy and modify
                      ($mod_str = $org_str) =~ s/.//;
                      die unless length($mod_str)+1 == length($org_str)
                   },
     substr_rhs => sub { # there's no point full string copy, simply copy what's needed
                      $mod_str = substr($org_str, 1);
                      die unless length($mod_str)+1 == length($org_str)
                   },
     substr_lhs => sub { # copy and modify 
                      substr($mod_str = $org_str, 0, 1) = '';
                      die unless length($mod_str)+1 == length($org_str)
                   },
     reversestr => sub { # reverse, copy, modify, reverse 
                      chop($mod_str = reverse($org_str));
                      $mod_str = reverse $mod_str;
                      die unless length($mod_str)+1 == length($org_str)
                   }
     }
  );
  print '- ' x 30, "\n"
}

##</code><code>##

string length: 20
                Rate reversestr substr_lhs regexsubst substr_rhs
reversestr 1120993/s         --       -12%       -13%       -48%
substr_lhs 1273691/s        14%         --        -1%       -41%
regexsubst 1289977/s        15%         1%         --       -40%
substr_rhs 2144546/s        91%        68%        66%         --
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
string length: 200
                Rate reversestr regexsubst substr_lhs substr_rhs
reversestr  741492/s         --       -37%       -39%       -61%
regexsubst 1172942/s        58%         --        -3%       -39%
substr_lhs 1211322/s        63%         3%         --       -37%
substr_rhs 1915850/s       158%        63%        58%         --
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
string length: 2000
               Rate reversestr substr_lhs regexsubst substr_rhs
reversestr 145793/s         --       -82%       -82%       -84%
substr_lhs 795724/s       446%         --        -4%       -11%
regexsubst 828896/s       469%         4%         --        -7%
substr_rhs 894365/s       513%        12%         8%         --
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
string length: 20000
               Rate reversestr substr_rhs regexsubst substr_lhs
reversestr  16427/s         --       -86%       -92%       -92%
substr_rhs 119927/s       630%         --       -39%       -41%
regexsubst 197394/s      1102%        65%         --        -3%
substr_lhs 202514/s      1133%        69%         3%         --
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - -