#!/usr/local/bin/perl5.8.0 or #!/usr/local/bin/perl5.6.1

use Benchmark; 
$main::x=join("",(a..z))x100;
 
&timethis(100,\&test);
 
sub test {
   $main::x =~ s/(.*?)I/$1/isge;
   }

##</code><code>##

Perl 5.8.0
timethis 1000: 48 wallclock secs (46.76 usr +  0.02 sys = 46.78 CPU) @ 21.38/s (n=1000) 

Perl 5.6.1
timethis 1000:  1 wallclock secs ( 0.70 usr +  0.00 sys =  0.70 CPU) @ 1428.57/s (n=1000) 

##</code><code>##

  Setting an EVAL scope, savestack=12
  24 <opqrstuvwx> <yz>    |  1:  OPEN1
  24 <opqrstuvwx> <yz>    |  3:  MINMOD
  24 <opqrstuvwx> <yz>    |  4:  STAR
  Setting an EVAL scope, savestack=12
                            failed...
  Setting an EVAL scope, savestack=12
  25 <opqrstuvwxy> <z>    |  1:  OPEN1
  25 <opqrstuvwxy> <z>    |  3:  MINMOD
  25 <opqrstuvwxy> <z>    |  4:  STAR
  Setting an EVAL scope, savestack=12
                            failed...
  Setting an EVAL scope, savestack=12
  26 <opqrstuvwxyz> <>    |  1:  OPEN1
  26 <opqrstuvwxyz> <>    |  3:  MINMOD
  26 <opqrstuvwxyz> <>    |  4:  STAR
  Setting an EVAL scope, savestack=12
                            failed...
Match failed

##</code><code>##

                           SANY can match 1 times out of 1...
  23 <opqrstuvw> <xyz>    |  6:    CLOSE1
  23 <opqrstuvw> <xyz>    |  8:    EXACTF <I>
                              failed...
                           SANY can match 1 times out of 1...
  24 <opqrstuvwx> <yz>    |  6:    CLOSE1
  24 <opqrstuvwx> <yz>    |  8:    EXACTF <I>
                              failed...
                           SANY can match 1 times out of 1...
  25 <opqrstuvwxy> <z>    |  6:    CLOSE1
  25 <opqrstuvwxy> <z>    |  8:    EXACTF <I>
                              failed...
                           SANY can match 1 times out of 1...
  26 <opqrstuvwxyz> <>    |  6:    CLOSE1
  26 <opqrstuvwxyz> <>    |  8:    EXACTF <I>
                              failed...
                           SANY can match 0 times out of 1...
                            failed...
Match failed