I have a sub called TEST() which converts every sort of input to a number. It should return 0 if the input value is undefined or uninitialized or blank or contains letters only. But if it contains digits, it should return those digits only.

So, if I ask to convert "55a" then it returns "55" which is fine. But if I try to convert "a55" then it returns 0, which baffles me! It should return 55. Why does this happen?

Edit: It seems like I am able to access the value of $N from within the warning exception, but I cannot modify it. The changes do not stick. So, I guess the question is how can I export the value of $N from within the warning sub { } so that it would overwrite the value of $N in the TEST sub?

#!/usr/bin/perl -w

use strict;
use warnings;

my @TEST_VALUES = ('55a', 'a55');

foreach my $i (@TEST_VALUES)
{
  print "Calling TEST('$i'): ";
  print "\nTEST return value = ", TEST($i), "\n";
}
exit;

#######################################
sub TEST
{
  print " TEST() was called ";
  defined $_[0] or return 0;
  my $N = shift;
  print "with argument: '$N'\n";

  # If we get a warning, it's probably because $N
  # is not a number. So, we remove all non-digits
  # and then it becomes a number!
  local $SIG{__WARN__} = sub { print "\t\t(((warning '$N'->"; $N =~ tr
+|0-9||cd; $N = "0$N"; print "'$N')))\n"; };

  $N += 0;
  print "\nThe value of N is now '$N'\n";
  return int($N);
}
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