A simple (and highly insecure) cipher is to rotate the alphabet by n letters and then substitute. For instance, rotating 13 letters gets you:

plaintext:   abcdef
ciphertext:  nopqrs
[download]

This is known as ROT-13. There is a simple solution for ROT-13 in Perl using tr///:

tr/A-Z/N-ZA-M/;
[download]

However, this is not easy to generalize to arbitrary rotation numbers.

Your challenge will be to come up with the shortest rotation cipher for an arbitrary number of rotations. The program should take two options on the command line. The first is the rotation number, and the second is a string to encipher. You may assume the first argument will be between 1 and 25, and the second argument will be all lowercase alphabetical characters in ASCII. It must print out the enciphered text on one line (newline not required).

My attempt:

#        1         2         3         4
# 3456789 123456789 123456789 123456789 123456
($n,$_)=@ARGV;split//;print chr(ord()+$n)for@_
[download]

46 strokes. Update: dragonchild points out a bug in this (Doh!).