#!/usr/bin/perl

my $tf = shift;		# any random text file. Say, /etc/passwd

open(MF, "< $tf") || die "Unable open $tf for input: $!";

# this doesn't work
#
my %opt;
$opt{'M'} = *MF;
while (<$opt{'M'}>) {
	print "loop one...\n";
}

# this doesn't work
#
my @opt;
$opt[0] = *MF;
while (<$opt[0]>) {
	print "loop two...\n";
}

# this does work
#
my $tf = *MF;
while (<$tf>) {
	print "loop three...\n";
}