Uner the same assumption, I prefer a regular expression. The Common module will match any valid number. The /e option will do the subtraction. The /r option returns the result without modifying the original string. 

use strict;
use warnings;
use Regexp::Common;
my $NUMBER = qr/$RE{num}{real}/;
my @array = ('31:15');
print $array[0] =~ s/($NUMBER):($NUMBER)/$1-$2/er;

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Bill

In reply to Re^2: Comapring two values of a scalar by BillKSmith
in thread Comapring two values of a scalar by bonny

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