Your problem hinges on the idea that $0 in perl is like $ARGV[0] in C. The perl variable $0 is actually the name of the program that is running. The command line args are stored in @ARGV. So you really want $ARGV[0] (like in c). Try running this code:

use strict;
use warnings;

{
    print "\$0 = $0\n";
    print "\$ARGV[0] = $ARGV[0]\n";
}
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Assume that the name of this script is arg_test.pl, run the command:

>perl -w arg_test.pl foo

which yields this output:

$0 = arg_test.pl
$ARGV[0] = foo
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The rest of your scripts behaviour should become clear.