Why does $ARGV[0] contains a newline? chop will remove the last character, no matter what it is. The following should be more reliable than chop:

my $arg = $ARGV[0];
$arg =~ s/\*$//;    # Remove trailing '*', if any.
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If there really is a newline, add chomp($arg) between those two lines.

Of course, you probably you could forget about removing the '*' and use File::Glob or File::DosGlob to interpret the argument (if you're trying to list the files matching the spec).