I wondered, how I could achieve that on various Unix platforms, and I ran the following command on my Linux box:
$ man -k base64
base64 (1) – base64 encode/decode data and print to standard output
MIME::Base64 (3pm) – Encoding and decoding of base64 strings
Right the utility base64 (beloning to GNU coreutils) would do it, if it were broadly available; on AIX you can’t expect GNU coreutils to be installed.
The MIME::Base64 man page shows a nice perl one-liner making use of a perl module, which is rather likely to be installed:
$ perl -MMIME::Base64 -ne ‘print decode_base64($_)’