(main.pl)
use strict;
use warnings;
use mySubs;

my @array;

while (my $temp=<INPUT>){
    my $number=&mySub(\$temp);
    @array=(@array,$number);
}
---------------------------
(mySubs.pm)
use strict;
use warnings;
package mySubs;
#...Exporter.. etc..

sub mySub
{
  my $variable = ${$_[0]};
....
#some stuff
....
  if (some condition){
     print "data $variable not valid in mySub\n";
     return -1;
  }
....
#rest of sub
....
}