umhmm you got my typo. i accidentally used $string instead of $str in my post first. that explains the high rates for the regex solution. here is the timing with the typo corrected: 
               Rate split_pos grep_split substr_map regexo regex subst
+r_loop unpack
split_pos    5587/s        --       -65%       -69%   -76%  -77%      
+  -79%   -81%
grep_split  15974/s      186%         --       -12%   -32%  -34%      
+  -40%   -45%
substr_map  18051/s      223%        13%         --   -23%  -26%      
+  -32%   -38%
regexo      23474/s      320%        47%        30%     --   -3%      
+  -12%   -20%
regex       24272/s      334%        52%        34%     3%    --      
+   -9%   -17%
substr_loop 26596/s      376%        66%        47%    13%   10%      
+    --    -9%
unpack      29240/s      423%        83%        62%    25%   20%      
+   10%     --

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-- Terry Pratchett, "Reaper Man"

In reply to Re^3: Splitting a string to chunks by Fengor
in thread Splitting a string to chunks by spurperl

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