pack(C) 19 June 1992 pack(C) Name pack, pcat, unpack - compress and expand files Syntax pack [ - ] name ... pcat name ... unpack name ... Description The pack command attempts to store the specified files in a compressed form. Wherever possible, each input file name is replaced by a packed file name.z with the same access modes, access and modified dates, and the owner of name. If pack is successful, name will be removed. Packed files can be restored to their original form using unpack or pcat. pack uses Huffman (minimum redundancy) codes on a byte-by-byte basis. If the ``-'' argument is used, an internal flag is set that causes pack to display information about the file compression. Additional occurrences of ``-'' in place of name will cause the internal flag to be set and reset. The amount of compression obtained depends on the size of the input file and the character frequency distribution. Because a decoding tree forms the first part of each .z file, it is usually not worthwhile to pack files smaller than three blocks, unless the character frequency distribu- tion is very scattered, which may occur with printer plots or pictures. Typically, text files are reduced to 60-75% of their original size. Load modules, which use a larger character set and have a more uniform distri- bution of characters, show little compression, the packed versions being about 90% of the original size. pack returns a value that is the number of files that it failed to compress. No packing will occur if: - The file appears to be already packed - The filename has more than 253 characters - The file has links - The file is a directory - The file cannot be opened - No disk storage blocks will be saved by packing - A file called name.z already exists - The .z file cannot be created - An I/O error occurred during processing The last segment of the filename must contain no more than 253 characters to allow space for the appended .z extension. Directories cannot be compressed. pcat does for packed files what cat(C) does for ordinary files. The specified files are unpacked and written to the standard output. To view a packed file named name.z use: pcat name.z or just: pcat name To make an unpacked copy, say nnn, of a packed file named name.z without destroying name.z, enter the command: pcat name > nnn pcat returns the number of files it was unable to unpack. Failure may occur if: - The filename (exclusive of the .z) has more than 253 characters - The file cannot be opened - The file does not appear to be the output of pack unpack expands files created by pack. For each file name specified in the command, a search is made for a file called name.z (or just name, if name ends in .z). If this file appears to be a packed file, it is replaced by its expanded version. The new file has the .z suffix stripped from its name, and has the same access modes, access and modifi- cation dates, and owner as those of the packed file. unpack returns a value that is the number of files it was unable to unpack. Failure may occur for the same reasons that it may in pcat, as well as in a file where the ``unpacked'' name already exists, or if the unpacked file cannot be created. Standards conformance pack, pcat and unpack are conformant with: AT&T SVID Issue 2; ANd X/Open Portability Guide, Issue 3, 1989.