#!/usr/bin/perl -w
use strict;
$|=1;

my $mode = lc($ARGV[0]);
($mode && $mode =~ /^(win|mac|unix)$/) or die(usage());
my $end = ($mode eq 'win' ? "\r\n" : ($mode eq 'mac' ? "\r" : "\n"));

my $file = $ARGV[1] or die(usage());
open(IN, "< $file") or die("Unable to open file [\"$file\": $!]");

my ($a, $b) = (0, 0);    # for reading two consecutive chars
while ($a || read(IN, $a, 1)) {
	if ($a =~ /^[\n\r]$/) {
		print $end;
		read(IN, $b, 1) or last;
		if ($b =~ /^[\n\r]$/ && $b ne $a) {    # \r\n or \n\r
			$a = 0;
		} else {
			$a = $b;    # save for next iteration
		}
	} else {
		print $a;
		$a = 0;
	}
}

close(IN) or die("Unable to close file [\"$file\": $!]");
exit;

sub usage {
	return "Usage:  $0 target filename > output\n where target = win, mac, or unix\n";
}

1;