use strict;
use warnings;

for(qw(1 4 haha)){
 usenumbers($_) or die($@);
}

sub usenumbers {
 my $var = shift;

 unless($var =~ /^\d+$/) {
    $@ = "Invalid Number";
    return;
 }

 print "Yes, [$var] has numbers.\n";
 return 1;
}