Pack is a legacy Unix shell compression program based on Huffman coding.
[1][2] The unpack utility will restore files to their original state after they have been compressed using the pack utility.
Although obsolete, support for packed files exists in modern compression tools such as gzip[3] and 7-zip.
Files can be returned to their original state using unpack.
In addition, there may also be a pcat command which reads in a compressed file and sends its output to stdout.