You might want to take a look at This Node

What I generally do if I need to recycle a variable in a sub routine is just call the variable at the beginning of the script.

#!/usr/bin/perl

use warnings;
use strict;

my $counter = 0;

&mySub;
&mySub;
&mySub;

sub mySub {
  print "My Value is ", $counter++, "\n";
}
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Since $counter exists before the sub is called, the sub inherits the variable and updating it should work fine.