perl + identify if param is empty value from ARG

Question

when I run the following script.pl script with no arguments:

./script.pl

I do not get the message No arg. Why? How to identify if $param is a null value or empty value, same as [ -z from ksh?

#!/usr/bin/perl
my $param = $ARGV[0];
if ($param = "") {
    print No arg;
} else {
    print arg: $param;
}

Answer 1

Because it's not Perl. Where did you learn that syntax? So much is wrong with it.

1. $param = "" assigns an empty string to $param, that's not what you want.

2. null is spelled undef in Perl.

3. To compare strings, use the eq operator.

4. You must quote strings: print "No arg"

Much easier:

#!/usr/bin/perl
if (@ARGV) {
    print 'have parameters';
} else {
    print q{don't have parameters};
}