Gzip

{{Infobox software

| name = gzip (software)

| logo = Gzip-Logo.svg

| author = {{plainlist|

}}

| developer = GNU Project

| released = {{Start date and age|df=yes|1992|10|31}}

| latest release version = {{wikidata|property|preferred|references|edit|Q283647|P348|P548=Q2804309}}

| latest release date = {{wikidata|qualifier|preferred|single|Q283647|P348|P548=Q2804309|P577}}

| latest preview version = {{wikidata|property|preferred|references|edit|Q283647|P348|P548=Q51930650}}

| latest preview date = {{wikidata|qualifier|preferred|single|Q283647|P348|P548=Q51930650|P577}}

| operating system = Unix-like, Plan 9, Inferno

| genre = Data compression

| programming language = C

| license = GPL-3.0-or-later

| website = {{URL|//www.gnu.org/software/gzip/}}

| repo = {{URL|//git.savannah.gnu.org/cgit/gzip.git}}

}}

gzip is a file format and a software application used for file compression and decompression. The program was created by Jean-loup Gailly and Mark Adler as a free software replacement for the compress program used in early Unix systems, and intended for use by GNU (from which the "g" of gzip is derived). Version 0.1 was first publicly released on 31 October 1992, and version 1.0 followed in February 1993.

The decompression of the gzip format can be implemented as a streaming algorithm, an important{{why|date=January 2025}} feature for Web protocols, data interchange and ETL (in standard pipes) applications.

File format

{{Infobox file format

| name = gzip (file format)

| extension = .gz

| mime = application/gzip{{cite IETF|title=The 'application/zlib' and 'application/gzip' Media Types|rfc=6713|publisher=Internet Engineering Task Force|access-date=2014-03-01}}

| uniform type = org.gnu.gnu-zip-archive

| magic = 1f 8b

| owner = Jean-loup Gailly and Mark Adler

| genre = Data compression

| url = {{URL|http://gzip.org}} (obsolete)

| open = Yes

}}

gzip is based on the DEFLATE algorithm, which is a combination of LZ77 and Huffman coding. DEFLATE was intended as a replacement for LZW and other patent-encumbered data compression algorithms which, at the time, limited the usability of the compress utility and other popular archivers.

"gzip" is often also used to refer to the gzip file format, which is:

a 10-byte header, containing a magic number (1f 8b), the compression method (08 for DEFLATE), 1-byte of header flags, a 4-byte timestamp, compression flags and the operating system ID.
optional extra headers as allowed by the header flags, including the original filename, a comment field, an "extra" field, and the lower half of a CRC-32 checksum for the header section.{{Cite web |last=Deutsch |first=L. Peter |date=May 1996 |title=GZIP file format specification version 4.3 |url=https://tools.ietf.org/html/rfc1952.html |journal= |language=en |publisher=Internet Engineering Task Force |doi=10.17487/RFC1952 |access-date=2019-07-23}}
a body, containing a DEFLATE-compressed payload
an 8-byte trailer, containing a CRC-32 checksum and the length of the original uncompressed data, modulo 2³².{{cite web|author1=Jean-loup Gailly|title=GNU Gzip|url=https://www.gnu.org/software/gzip/manual/gzip.html#index-options-4|website=Gnu.org|access-date=11 October 2015|archive-date=15 October 2015|archive-url=https://web.archive.org/web/20151015064748/http://www.gnu.org/software/gzip/manual/gzip.html#index-options-4|url-status=live}}

File:Targzip.svg program to compress multiple files.]]

Although its file format also allows for multiple such streams to be concatenated (gzipped files are simply decompressed concatenated as if they were originally one file),{{cite web| title=GNU Gzip: Advanced usage| url=https://www.gnu.org/software/gzip/manual/html_node/Advanced-usage.html| website=Gnu.org| access-date=2012-11-28| archive-date=24 December 2012| archive-url=https://web.archive.org/web/20121224211417/https://www.gnu.org/software/gzip/manual/html_node/Advanced-usage.html| url-status=live}} gzip is normally used to compress just single files.{{cite web| title=Can gzip compress several files into a single archive?| url=http://www.gzip.org/#faq16|website=Gnu.org| access-date=2010-01-27 |archive-url=https://web.archive.org/web/20100722004012/http://www.gzip.org/#faq16 |archive-date=2010-07-22}} Compressed archives are typically created by assembling collections of files into a single tar archive (also called tarball),{{cite web|title=tarball, The Jargon File, version 4.4.7|url=http://www.catb.org/jargon/html/T/tarball.html|website=Catb.org|access-date=2010-01-27|archive-date=20 March 2017|archive-url=https://web.archive.org/web/20170320183848/http://www.catb.org/jargon/html/T/tarball.html|url-status=live}} and then compressing that archive with gzip. The final compressed file usually has the extension {{mono|.tar.gz}} or {{mono|.tgz}}.

gzip is not to be confused with the ZIP archive format, which also uses DEFLATE. The ZIP format can hold collections of files without an external archiver, but is less compact than compressed tarballs holding the same data, because it compresses files individually and cannot take advantage of redundancy between files (solid compression).

The gzip file format is also not to be confused with that of the compress utility, based on LZW, with extension {{mono|.Z}}; however, the gunzip utility is able to decompress .Z files.{{cite web | title=GNU Gzip | website=The GNU Operating System and the Free Software Movement | date=2023-02-05 | url=https://www.gnu.org/software/gzip/manual/gzip.html | access-date=2024-04-03 |quote=gunzip can currently decompress files created by gzip, zip, compress or pack. The detection of the input format is automatic. }}

Implementations

{{Infobox software

| name = NetBSD Gzip / FreeBSD Gzip

| developer = The NetBSD Foundation

| genre = Data compression

| programming language = C

| license = Simplified BSD License

| website = hide

| repo = {{URL|//cvsweb.netbsd.org/bsdweb.cgi/src/usr.bin/gzip/}}

}}

Various implementations of the program have been written. The most commonly known is the GNU Project's implementation using Lempel-Ziv coding (LZ77). OpenBSD's version of gzip is actually the compress program, to which support for the gzip format was added in OpenBSD 3.4. The 'g' in this specific version stands for gratis.{{cite web|url=https://man.openbsd.org/gzip.1#HISTORY|title=OpenBSD gzip(1) manual page|website=Openbsd.org|access-date=2018-02-04|publisher=OpenBSD}} FreeBSD, DragonFly BSD and NetBSD use a BSD-licensed implementation instead of the GNU version; it is actually a command-line interface for zlib intended to be compatible with the GNU implementations' options.{{cite web|url=http://man.freebsd.org/gzip|title=gzip|publisher=Man.freebsd.org|date=2011-10-09|access-date=2014-03-01|archive-date=17 December 2019|archive-url=https://web.archive.org/web/20191217104949/https://www.freebsd.org/cgi/man.cgi?gzip|url-status=live}} These implementations originally come from NetBSD, and support decompression of bzip2 and the Unix pack format.

An alternative compression program achieving 3-8% better compression is Zopfli. It achieves gzip-compatible compression using more exhaustive algorithms, at the expense of compression time required. It does not affect decompression time.

pigz, written by Mark Adler, is compatible with gzip and speeds up compression by using all available CPU cores and threads.{{cite web|url=https://zlib.net/pigz/|author=Mark Adler|website=zlib.net|title=pigz: A parallel implementation of gzip for modern multi-processor, multi-core machines|date=2017|access-date=23 December 2018|archive-date=18 December 2018|archive-url=https://web.archive.org/web/20181218151754/http://zlib.net/pigz/|url-status=live}}

= Damage recovery =

Data in blocks prior to the first damaged part of the archive is usually fully readable. Data from blocks not demolished by damage that are located afterward may be recoverable through difficult workarounds.[https://web.archive.org/web/20180708075208/http://www.gzip.org/recover.txt Recovering a damaged .gz file – Jean-loup Gailly, GZip.org]

Derivatives and other uses

The tar utility included in most Linux distributions can extract .tar.gz files by passing the {{mono|z}} option, e.g., {{mono|tar -zxf file.tar.gz}}, where -z instructs decompression, -x means extraction, and -f specifies the name of the compressed archive file to extract from. Optionally, -v (verbose) lists files as they are being extracted.{{cite web |title=How To Extract / Unzip tar.gz Files From Linux Command Line |url=https://phoenixnap.com/kb/extract-tar-gz-files-linux-command-line |website=Knowledge Base by phoenixNAP |access-date=12 January 2022 |date=14 November 2019}}

zlib is an abstraction of the DEFLATE algorithm in library form which includes support both for the gzip file format and a lightweight data stream format in its API. The zlib stream format, DEFLATE, and the gzip file format were standardized respectively as RFC 1950, RFC 1951, and RFC 1952.

The gzip format is used in HTTP compression, a technique used to speed up the sending of HTML and other content on the World Wide Web. It is one of the three standard formats for HTTP compression as specified in RFC 2616. This RFC also specifies a zlib format (called "DEFLATE"), which is equal to the gzip format except that gzip adds eleven bytes of overhead in the form of headers and trailers. Still, the gzip format is sometimes recommended over zlib because Internet Explorer does not implement the standard correctly and cannot handle the zlib format as specified in RFC 1950.{{cite web |first=Eric |last=Lawrence |title=Compressing the Web |url=http://blogs.msdn.com/b/ieinternals/archive/2014/10/21/http-compression-optimize-file-formats-with-deflate.aspx |date=21 November 2014 |website=MSDN Blogs > IEInternals |publisher=Microsoft |access-date=2 November 2015 |archive-date=28 October 2015 |archive-url=https://web.archive.org/web/20151028172035/http://blogs.msdn.com/b/ieinternals/archive/2014/10/21/http-compression-optimize-file-formats-with-deflate.aspx |url-status=live }}

zlib DEFLATE is used internally by the Portable Network Graphics (PNG) format.

Since the late 1990s, bzip2, a file compression utility based on a block-sorting algorithm, has gained some popularity as a gzip replacement. It produces considerably smaller files (especially for source code and other structured text), but at the cost of memory and processing time (up to a factor of 4).{{cite web |url=http://compressionratings.com/comp.cgi?7-zip+9.12b++bzip2+1.0.5++gzip+1.3.3+-5 |title=Comparison Tool: 7-zip vs bzip2 vs gzip | website=compressionratings.com |access-date=1 November 2014 |url-status=dead |archive-url=https://web.archive.org/web/20141101212919/http://compressionratings.com/comp.cgi?7-zip+9.12b++bzip2+1.0.5++gzip+1.3.3+-5 |archive-date=1 November 2014 }}

AdvanceCOMP, Zopfli, libdeflate and 7-Zip can produce gzip-compatible files, using an internal DEFLATE implementation with better compression ratios than gzip itself—at the cost of more processor time compared to the reference implementation.{{citation needed|date=December 2018}}

Research published in 2023 showed that simple lossless compression techniques such as gzip could be combined with a k-nearest-neighbor classifier to create an attractive alternative to deep neural networks for text classification in natural language processing. This approach has been shown to equal and in some cases outperform conventional approaches such as BERT due to low resource requirements, e.g. no requirement for GPU hardware.{{Cite journal |last1=Jiang |first1=Zhiying |last2=Yang |first2=Matthew |last3=Tsirlin |first3=Mikhail |last4=Tang |first4=Raphael |last5=Dai |first5=Yiqin |last6=Lin |first6=Jimmy |date=July 2023 |title="Low-Resource" Text Classification: A Parameter-Free Classification Method with Compressors |url=https://aclanthology.org/2023.findings-acl.426 |journal=Findings of the Association for Computational Linguistics: ACL 2023 |location=Toronto, Canada |publisher=Association for Computational Linguistics |pages=6810–6828|doi=10.18653/v1/2023.findings-acl.426 |s2cid=260668487 |doi-access=free }}

Notes

References

[https://tools.ietf.org/html/rfc1952 RFC 1952] {{Webarchive|url=https://web.archive.org/web/20190728213743/https://tools.ietf.org/html/rfc1952 |date=28 July 2019 }} – GZIP file format specification version 4.3