You could also do something like that:

# Test if the is an argument
if(!@ARGV)
        {
        die "My help message\n";
        }

# Test if the argument is a file
if(! -e $ARGV[0])
        {
        print "File $ARGV[0] does not exist\n";
        }
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[]'s -DBC

Edited by Chady -- code tags, escaped a [