If you want to make the regex solution run much more quickly, use Look Around Assertions in place of the capture and reinsert. 

cmpthese(0, {
              substr => sub {
                  my @l = @list;
                  substr $_, -2, 0, '.' for @l;
              },
              regex => sub {
                  my @l = @list;
                  s/(..)$/.$1/ for @l;
              },
              regex2 => sub {
                  my @l = @list;
                  s/(?=..)$/./ for @l;
              },
             });

[download]
yields 
         Rate substr  regex regex2
substr 73.1/s     --   -39%   -71%
regex   121/s    65%     --   -52%
regex2  250/s   242%   107%     --

[download]

Update: As per JavaFan's comment, I had a typo in my sub. Replaced s/(?=..)$/./ with s/(?=..$)/./ which returns the correct result, but at substantially poorer performance.

#11929 First ask yourself `How would I do this without a computer?' Then have the computer do it the same way.

In reply to Re^2: Print Number With Implied Decimal Point by kennethk
in thread Print Number With Implied Decimal Point by j355ga

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