Looks like you tried to write \[31:15\] rather than use code tags. See Markup in the Monastery for help with posting questions.

Taking a bit of a guess but you probably have something like $array[0]= "31:15";. If so, just split on the ":" and do the subtraction. This should be simply enough for a beginner (sorry for the assumption) but if it gets confusing, try the same thing on a simple variable (scalar) like $foo= "31:15";.

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

Regexp::Common

While nice and general, this seems a bit heavy for the OP, especially considering the the rather regular examples given. Of course, always nice to see an example of a more general/powerful solution.

And then plz try to rephrase your question, the code given doesn't look like Perl and your examples are cryptic...