magnetify - shell script to convert magnet hashes to links

#!/bin/sh

# magnetify - dress up a magnet hash so you can make it clickable or use it in a torrent client
#             that supports magnet links, like tranmission (www.transmissionbt.com/‎).
#
# HEY!: why can't you just add the magnet hash directly into the torrent client?
#
# Language: sh
# Author: Burton Samograd <burton@samograd.ca>
# License: GPL3 or higher if applicable
# Copyleft 2014

# The idiom ${x?"error message"} will test to see if the variable is set, and print the
# message "error message" and exit the shell (returning an error code) if it isn't.
#
# $1 is the first command line argument given to the script, followed by $2, $3...
# It's good to put these $n variables into names at the top of the script so you
# don't lose track of them.  Good variable names are very im-por-tant.
#
# To get all arguments usefully use "$@" (don't ask), but if you don't have spaces
# in your filenames (I mean, who does that these days?) you can use the old skool $*
#
hash=${1?"usage: magnetify <torrent magnet link hash>"}
echo "magnet:?xt=urn:btih:$hash"

exit 0 # return success, but don't dot (.) this or you'll kill your shell

# tested with 71b4bcd801233939144ebf24ecf33d0fbdb6f317, #worksforme