GZIP(1) USER COMMANDS GZIP(1) NAME gzip, gunzip, zcat - compress or expand files SYNOPSIS gzip [ -cdfhLrtvV19 ] [ _n_a_m_e ... ] gunzip [ -cfhLrtvV ] [ _n_a_m_e ... ] zcat [ -hLV ] [ _n_a_m_e ... ] DESCRIPTION _G_z_i_p reduces the size of the named files using Lempel-Ziv coding (LZ77). Whenever possible, each file is replaced by one with the extension .z, while keeping the same ownership modes, access and modification times. (The extension is -z for VMS, z for MSDOS, OS/2 and Atari.) If no files are specified, the standard input is compressed to the standard output. If the new file name is too long, _g_z_i_p truncates it and keeps the original file name in the compressed file. _G_z_i_p will only attempt to compress regular files. In par- ticular, it will ignore symbolic links. Compressed files can be restored to their original form using _g_z_i_p -_d or _g_u_n_z_i_p or _z_c_a_t. _g_u_n_z_i_p takes a list of files on its command line and replaces each file whose name ends with .z or .Z or -z and which begins with the correct magic number with an uncompressed file without the original extension. _g_u_n_z_i_p also recognizes the special extensions .tgz and .taz as shorthands for .tar.z or .tar.Z _g_u_n_z_i_p can currently decompress files created by _g_z_i_p, _z_i_p, _c_o_m_p_r_e_s_s or _p_a_c_k. The detection of the input format is automatic. When using the first two formats, _g_u_n_z_i_p checks a 32 bit CRC. For _p_a_c_k, _g_u_n_z_i_p checks the uncompressed length. The _c_o_m_p_r_e_s_s format was not designed to allow con- sistency checks. However _g_u_n_z_i_p is sometimes able to detect a bad .Z file. If you get an error when uncompressing a .Z file, do not assume that the .Z file is correct simply because the standard _u_n_c_o_m_p_r_e_s_s does not complain. This gen- erally means that the standard _u_n_c_o_m_p_r_e_s_s does not check its input, and happily generates garbage output. Files created by _z_i_p can be uncompressed by gzip only if they have a single member compressed with the 'deflation' method. This feature is only intended to help conversion of tar.zip files to the tar.z format. To extract zip files with several members, use _u_n_z_i_p instead of _g_u_n_z_i_p. _z_c_a_t is identical to _g_u_n_z_i_p -c. (On some systems, _z_c_a_t may be installed as _g_z_c_a_t to preserve the original link to _c_o_m_p_r_e_s_s.) _z_c_a_t uncompresses either a list of files on the command line or its standard input and writes the Sun Release 4.1 Last change: local 1 GZIP(1) USER COMMANDS GZIP(1) uncompressed data on standard output. _z_c_a_t will uncompress files that have the correct magic number whether they have a .z suffix or not. _G_z_i_p uses the Lempel-Ziv algorithm used in _z_i_p and PKZIP. The amount of compression obtained depends on the size of the input and the distribution of common substrings. Typi- cally, text such as source code or English is reduced by 60-70%. Compression is generally much better than that achieved by LZW (as used in _c_o_m_p_r_e_s_s), Huffman coding (as used in _p_a_c_k), or adaptive Huffman coding (_c_o_m_p_a_c_t). Compression is always performed, even if the compressed file is slightly larger than the original. The worst case expan- sion is a few bytes for the gzip file header, plus 5 bytes every 32K block, or an expansion ratio of 0.015% for large files. _g_z_i_p preserves the mode, ownership and timestamps of files when compressing or decompressing. OPTIONS -c --stdout Write output on standard output; keep original files unchanged. If there are several input files, the out- put consists of a sequence of independently compressed members. To obtain better compression, concatenate all input files before compressing them. -d --decompress Decompress. -f --force Force compression or decompression even if the file has multiple links or the corresponding file already exists. If -f is not given, and when not running in the background, _g_z_i_p prompts to verify whether an existing file should be overwritten. -h --help Display a help screen. -L --license Display the _g_z_i_p license. -q --quiet Suppress all warnings. -r --recurse Travel the directory structure recursively. If any of the file names specified on the command line are direc- tories, _g_z_i_p will descend into the directory and compress all the files it finds there (or decompress Sun Release 4.1 Last change: local 2 GZIP(1) USER COMMANDS GZIP(1) them in the case of _g_u_n_z_i_p ). -t --test Test. Check the compressed file integrity. -v --verbose Verbose. Display the name and percentage reduction for each file compressed. -V --version Version. Display the version number and compilation options. -# --fast --best Regulate the speed of compression using the specified digit #, where -1 or --fast indicates the fastest compression method (less compression) and -9 or --best indicates the slowest compression method (optimal compression). The default compression level is -5. ADVANCED USAGE Multiple compressed files can be concatenated. In this case, _g_u_n_z_i_p will extract all members at once. For example: gzip -c file1 > foo.z gzip -c file2 >> foo.z Then gunzip -c foo is equivalent to cat file1 file2 In case of damage to one member of a .z file, other members can still be recovered (if the damaged member is removed). However, you can get better compression by compressing all members at once: cat file1 file2 | gzip > foo.z compresses better than gzip -c file1 file2 > foo.z If you want to recompress concatenated files to get better compression, do: zcat old.z | gzip > new.z ENVIRONMENT The environment variable GZIP can hold a set of default options for _g_z_i_p. These options are interpreted first and can be overwritten by explicit command line parameters. For Sun Release 4.1 Last change: local 3 GZIP(1) USER COMMANDS GZIP(1) example: for sh: GZIP="-8 -v"; export GZIP for csh: setenv GZIP "-8 -v" for MSDOS: set GZIP=-8 -v On Vax/VMS, the name of the environment variable is GZIP_OPT, to avoid a conflict with the symbol set for invo- cation of the program. SEE ALSO znew(1), zcmp(1), zmore(1), zforce(1), gzexe(1), zip(1), unzip(1), compress(1), pack(1), compact(1) DIAGNOSTICS Exit status is normally 0; if an error occurs, exit status is 1. If a warning occurs, exit status is 2. Usage: gzip [-cdfhLrtvV19] [file ...] Invalid options were specified on the command line. _f_i_l_e: not in gzip format The file specified to _g_u_n_z_i_p has not been compressed. _f_i_l_e: Corrupt input. Use zcat to recover some data. The compressed file has been damaged. The data up to the point of failure can be recovered using zcat file > recover _f_i_l_e: compressed with _x_x bits, can only handle _y_y bits _F_i_l_e was compressed (using LZW) by a program that could deal with more _b_i_t_s than the decompress code on this machine. Recompress the file with gzip, which compresses better and uses less memory. _f_i_l_e: already has z suffix -- no change The file is assumed to be already compressed. Rename the file and try again or use zcat. _f_i_l_e already exists; do you wish to overwrite (y or n)? Respond "y" if you want the output file to be replaced; "n" if not. gunzip: corrupt input A SIGSEGV violation was detected which usually means that the input file has been corrupted. _x_x._x% Percentage of the input saved by compression. (Relevant only for -v.) -- not a regular file or directory: ignored When the input file is not a regular file or direc- tory, (e.g. a symbolic link, socket, FIFO, device file), it is left unaltered. -- has _x_x other links: unchanged The input file has links; it is left unchanged. See _l_n(1) for more information. Use the -f flag to force compression of multiply-linked files. Sun Release 4.1 Last change: local 4 GZIP(1) USER COMMANDS GZIP(1) CAVEATS The .z extension is already used by _p_a_c_k(1). You can link _g_z_i_p to _p_c_a_t to get transparent decompression for programs expecting .z files to be in _p_a_c_k format. Sun Release 4.1 Last change: local 5