Close but no cigar, you can't xor arbitrary strings that way. The following will cipher STDIN to STDOUT using the contents of the keyfile on the command line. Assumption is that the key file is much smaller than memory (maybe 5% or less): 
use warnings;
use strict;

@ARGV or die "Usage: cipher keyfile < source > dest\n";

open K,shift or die "Can't open keyfile: $!\n";
undef $/; my $k = <K>; close K; # slurp
length $k or die "error reading key file\n";

while (read STDIN, my $t, length $k)
{
  my @k = unpack "C*", $k; 
  print pack "C*", map { $_^shift @k } unpack "C*", $t;
}

[download]
Now let's try it: 
# make a key file, ok for demo purposes
$ perl -e 'print chr int rand 256 for 0..10000' > key.file

# make a test source file
$ ls -al /dev > plain.txt

# encipher
$ perl cipher.pl key.file < plain.txt > cipher.txt

# decipher
$ perl cipher.pl key.file < cipher.txt > deciphered.txt

# verify
$ diff -s plain.txt deciphered.txt 
Files plain.txt and deciphered.txt are identical

[download]

~%{${@_[0]}}->{0}&&+++ NO CARRIER

In reply to Re: Re: Mod-2 add 2 binary files by zude
in thread Mod-2 add 2 binary files by tperdue

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.