note GrandFather <p>There are many issues with your code. First off though, always use strictures (use [doc://strict]; use [doc://warnings]; - see [id://686571]). You use warnings, but strict is at least as important for catching errors. As another general coding tip: don't use the same name for multiple variables. In your sample code you use both $pro and @pro as well as @tetra and $tetra.</p> <p>Although it is often a good idea to give a manifest constant a name so the intent of the constant is clear, using a variable for 1 called $one adds no information and is likely to cause confusion just because there seems no reason to use the variable.</p> <p>Your "uninitialized value" variable warning is because you use @+ before the first regular expression match.</p> <p>You aren't getting the number of iterations in the loop you expect because you update @pro within the loop. That is almost always a bad idea.</p> <p>There are many ways to skin this cat. One trick is to use a look ahead match and take advantage of the fact that the regular expression engine doesn't allow successive matches at the same position. Consider:</p> <c> #!/usr/bin/perl use warnings; use strict; my $pro = "ABCDEFGH"; my @tetras; push @tetras, [$1, $+[0] + 1] while $pro =~ /(?=(.{4}))/g; print "$_->[0] -> Starting at pos $_->[1]\n" for @tetras; </c> <p>Prints:</p> <c> ABCD -> Starting at pos 1 BCDE -> Starting at pos 2 CDEF -> Starting at pos 3 DEFG -> Starting at pos 4 EFGH -> Starting at pos 5 </c> <div class="pmsig"><div class="pmsig-461912"> True laziness is hard work </div></div> 1005077 1005077