GZIP (1) Public-Domain Utilities GZIP (1) NAME gzip, gunzip, zcat - compress or expand files SYNOPSIS pgzipq q[p -acdfhlLnrtvV19 q]pqpq q[p-Sqsuffixp]qpq [ pname ...q ] pgunzipq q[p -acfhlLnrtvV q]pqpq q[p-Sqsuffixp]qpq [ pname ...q ] pzcatq q[p -fhLV q]pqpq [ pname ...q ] DESCRIPTION pGzipq reduces the size of the named files using Lempel-Ziv coding (LZ77). Whenever possible, each file is replaced by one with the extension p.gz,q while keeping the same ownership modes, access and modification times. (The default extension is p-gzq for VMS, pzq for MSDOS, OS/2 FAT and Atari.) If no files are specified, the standard input is compressed to the standard output. pGzipq will only attempt to compress regular files. In particular, it will ignore symbolic links. If the new file name is too long for its file system, pgzipq truncates it and keeps the original file name in the compressed file. pGzipq attempts to truncate only the parts of the file name longer than 3 characters. (A part is delimited by dots.) If the name consists of small parts only, the longest parts are truncated. For example, if file names are limited to 14 characters, gzip.msdos.exe is compressed to gzi.msd.exe.gz. Names are not truncated on systems which do not have a limit on file name length. Compressed files can be restored to their original form using pgzipq-d or pgunzipq or pzcat.q If the original name saved in the compressed file is not suitable for its file system, a new name is constructed from the original one to make it legal. pgunzipq takes a list of files on its command line and replaces each file whose name ends with .gz, -gz, .z, -z, _z or .Z and which begins with the correct magic number with an uncompressed file without the original extension. pgunzipq also recognizes the special extensions p.tgzq and p.tazq as shorthands for p.tar.gzq and p.tar.Zq respectively. When compressing, pgzipq uses the p.tgzq extension if necessary instead of truncating a file with a p.tarq extension. pgunzipq can currently decompress files created by pgzip,qzip, or ppack.q The detection of the input format is automatic. When using the first two formats, pgunzipq checks a 32 bit CRC. For ppack,qgunzip checks the uncompressed length. The standard pcompressq format was not designed to allow consistency checks. However pgunzipq 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 puncompressq does not complain. This generally means that the standard puncompressq does not check its input, and happily generates garbage output. The SCO compress -H format (lzh Tue Jan 4 23:11:06 1994 Page 1 GZIP (1) Public-Domain Utilities GZIP (1) compression method) does not include a CRC but also allows some consistency checks. Files created by pzipq 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.gz format. To extract zip files with several members, use punzipq instead of pgunzip.q pzcatq is identical to pgunzipq p-c.q (On some systems, pzcatq may be installed as pgzcatq to preserve the original link to pcompress.)q pzcatq uncompresses either a list of files on the command line or its standard input and writes the uncompressed data on standard output. pzcatq will uncompress files that have the correct magic number whether they have a p.gzq suffix or not. pGzipq uses the Lempel-Ziv algorithm used in pzipq and PKZIP. The amount of compression obtained depends on the size of the input and the distribution of common substrings. Typically, 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 pcompressq),pqpq Huffman coding (as used in ppackq),pqpq or adaptive Huffman coding q(pcompactq).pqpq Compression is always performed, even if the compressed file is slightly larger than the original. The worst case expansion 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. Note that the actual number of used disk blocks almost never increases. pgzipq preserves the mode, ownership and timestamps of files when compressing or decompressing. OPTIONS -a --ascii Ascii text mode: convert end-of-lines using local conventions. This option is supported only on some non-Unix systems. For MSDOS, CR LF is converted to LF when compressing, and LF is converted to CR LF when decompressing. -c --stdout --to-stdout Write output on standard output; keep original files unchanged. If there are several input files, the output consists of a sequence of independently compressed members. To obtain better compression, concatenate all input files before compressing them. -d --decompress --uncompress Decompress. -f --force Force compression or decompression even if the file has multiple links or the corresponding file already exists, Tue Jan 4 23:11:06 1994 Page 2 GZIP (1) Public-Domain Utilities GZIP (1) or if the compressed data is read from or written to a terminal. If the input data is not in a format recognized by pgzip,q and if the option --stdout is also given, copy the input data without change to the standard ouput: let pzcatq behave as pcat.q If p-fq is not given, and when not running in the background, pgzipq prompts to verify whether an existing file should be overwritten. -h --help Display a help screen and quit. -l --list For each compressed file, list the following fields: compressed size: size of the compressed file uncompressed size: size of the uncompressed file ratio: compression ratio (0.0% if unknown) uncompressed_name: name of the uncompressed file The uncompressed size is given as -1 for files not in gzip format, such as compressed .Z files. To get the uncompressed size for such a file, you can use: zcat file.Z | wc -c In combination with the --verbose option, the following fields are also displayed: method: compression method crc: the 32-bit CRC of the uncompressed data date & time: time stamp for the uncompressed file The compression methods currently supported are deflate, compress, lzh (SCO compress -H) and pack. The crc is given as ffffffff for a file not in gzip format. With --verbose, the size totals and compression ratio for all files is also displayed, unless some sizes are unknown. With --quiet, the title and totals lines are not displayed. -L --license Display the pgzipq license and quit. -n --no-name When compressing, do not save the original file name by default. (The original name is always saved if the name had to be truncated.) When decompressing, do not restore the original file name if present: remove only the pgzipq suffix from the compressed file name. -q --quiet Suppress all warnings. -r --recurse Travel the directory structure recursively. If any of the file names specified on the command line are directories, pgzipq will descend into the directory and compress all the files it finds there (or decompress them in the case of pgunzipq ). Tue Jan 4 23:11:06 1994 Page 3 GZIP (1) Public-Domain Utilities GZIP (1) -S .suf --suffix .suf Use suffix .suf instead of .gz. Any suffix can be given, but suffixes other than .z and .gz should be avoided to avoid confusion when files are transferred to other. A null suffix forces gunzip to try decompression on all given files regardless of suffix, as in: gunzip -S "" * (*.* for MSDOS) Previous versions of gzip used the .z suffix. This was changed to avoid a conflict with ppackq(1)p.qpq -t --test Test. Check the compressed file integrity. -v --verbose Verbose. Display the name and percentage reduction for each file compressed or decompressed. -V --version Version. Display the version number and compilation options then quit. -# --fast --best Regulate the speed of compression using the specified digit p#q,pqpq where p-1q or p--fastq indicates the fastest compression method (less compression) and p-9q or p--bestq indicates the slowest compression method (optimal compression). The default compression level is p-6qpqpq (that is, biased towards high compression at expense of speed). ADVANCED USAGE Multiple compressed files can be concatenated. In this case, pgunzipq will extract all members at once. For example: gzip -c file1 > foo.gz gzip -c file2 >> foo.gz Then gunzip -c foo is equivalent to cat file1 file2 In case of damage to one member of a .gz 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.gz compresses better than gzip -c file1 file2 > foo.gz If you want to recompress concatenated files to get better compression, do: zcat old.gz | gzip > new.gz If a compressed file consists of several members, the uncompressed size and CRC reported by the --list option applies to the last member only. Tue Jan 4 23:11:06 1994 Page 4 GZIP (1) Public-Domain Utilities GZIP (1) ENVIRONMENT The environment variable pGZIPq can hold a set of default options for pgzip.q These options are interpreted first and can be overwritten by explicit command line parameters. For 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 invocation 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 [-cdfhlLnrtvV19] [-S suffix] [file ...] Invalid options were specified on the command line. pfileq:pqpq not in gzip format The file specified to pgunzipq has not been compressed. pfile:qpqpq 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 pfileq:pqpq compressed with pxxq bits, can only handle pyyq bits pFileq was compressed (using LZW) by a program that could deal with more pbitsq than the decompress code on this machine. Recompress the file with gzip, which compresses better and uses less memory. pfileq:pqpq already has .gz suffix -- no change The file is assumed to be already compressed. Rename the file and try again. pfileq 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. pxx.x%q Percentage of the input saved by compression. (Relevant only for p-vqpqpq and p-lq.)pqpq -- not a regular file or directory: ignored When the input file is not a regular file or directory, (e.g. a symbolic link, socket, FIFO, device file), it is left unaltered. -- has pxxq other links: unchanged The input file has links; it is left unchanged. See plnq(1)pqpq for more information. Use the p-fq flag to force compression of multiply-linked files. CAVEATS When writing compressed data to a tape, it is generally necessary to pad the output with zeroes up to a block boundary. When the data is read and the whole block is passed to pgunzipq for decompression, pgunzipq detects that there is extra trailing garbage after the compressed data and emits a warning by default. You have to use the --quiet option to suppress the warning. This option can be set in the pGZIPq environment Tue Jan 4 23:11:06 1994 Page 5 GZIP (1) Public-Domain Utilities GZIP (1) variable as in: for sh: GZIP="-q" tar xfz /dev/rmt/datn for csh: (setenv GZIP "-q"; tar xfz /dev/rmt/datn) In the above example, gzip is invoked implicitly by the -z option of GNU tar. Make sure that the same block size (-b option of tar) is used for reading and writing compressed data on tapes. BUGS The --list option reports incorrect sizes if they exceed 2 gigabytes. The --list option reports sizes as -1 and crc as ffffffff if the compressed file is on a non seekable media. This manual page describes the UNIX version of pgzipq . COPYRIGHT pGzipq is not part of the Hermes package. Its use and distribution are governed by the Gnu Public License. Tue Jan 4 23:11:06 1994 Page 6