There are many issues with your code. First off though, always use strictures (use strict; use warnings; - see The strictures, according to Seuss). 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.

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.

Your "uninitialized value" variable warning is because you use @+ before the first regular expression match.

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.

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:

#!/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;

[download]

Prints:

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

[download]
True laziness is hard work

In reply to Re: Is it possible to get all tetra words with correct starting position using a better code within a loop? by GrandFather
in thread Is it possible to get all tetra words with correct starting position using a better code within a loop? by supriyoch_2008

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