Base64 decoding routine written entirely in bash, with no external dependencies.

Usage:
  base64decode < input > output

This code is absurly inefficient; it runs aproximately 12,000 times slower than
the perl-based decoder. The difference is that this code doesn't require you to
install any external programs, which may be important in some cases.

To decode using perl instead, use the following:

base64decode() {
   perl -e 'use MIME::Base64 qw(decode_base64);$/=undef;print decode_base64(<>);'
}