pack compresses files using a Huffman minimal redundancy code on a byte basis. Each file is compressed in place; the resulting file has a .z extension appended to the file name, but keeps the same owner and permissions. The times of last access and last modification are also preserved.

Packed files can be identified by file and uncompressed by unpack (which unpacks the file in place) or pcat (which unpacks to the standard output).

Normally pack reports the degree of compression achieved in each file, printing the report to standard output. This number can be negative, especially for small files with little redundancy in their contents, if the -f option is used.

pack does not pack files if:

• The file appears to have already been packed. 
• The file name is too long (an error will occur if it already has a .z extension). 
• The file has links or is a directory. 
• The packed file would be larger than the existing file (this includes empty files). 
• The destination file already exists, or there is an error in processing.

pack [[-][-B] [-f] [-o file] file] ...

Options

pack -o out1 in1 -o out2 in2

Exit Codes

pack myfile.txt

Packs the file myfile.txt and renames that file to myfile.txt.z. On successful completion, pack will report compression statistics similar to the following:

pack: myfile.txt: -1.8% Compression