...Triplets of 8-bit octets are encoded as groups of four characters, each representing 6 bits of the source 24 bits. Only characters present in all variants of ASCII and EBCDIC are used, avoiding incompatibilities in other forms of encoding such as uuencode/uudecode.
base64 is a command line utility which encodes and decodes files in this format. It can be used within a pipeline as an encoding or decoding filter, and is most commonly used in this manner as part of an automated mail processing system.