3. Linux / Unix Command: gzip
• gzip is a fast and efficient compression
program
– .gz filename extension
– gzip test.txt
• By default, gzip keeps the original file
name and timestamp in the compressed
file.
4. gzip Synopsis
• gzip [ -acdfhlLnNrtvV19 ] [-S suffix] [ name ... ]
• gunzip [ -acfhlLnNrtvV ] [-S suffix] [ name ... ]
• zcat [ -fhLV ] [ name ... ]
• gunzip also recognizes the special
extensions .tgz and .taz as shorthands
for .tar.gz and .tar.Z respectively.
5. gzip OPTIONS
• -c --stdout --to-stdout
– Write output on standard output
– keeps original files unchanged.
– If there are several input files, the output
consists of a sequence of independently
compressed members
• -f –force
– Force compression or decompression even if
the file has multiple links or the corresponding
file already exists
6. gzip OPTIONS
• -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
7. • -n --no-name
– When compressing, do not save the original file
name and time stamp by default.
– When decompressing, do not restore the original
file name if present (remove only the gzip suffix
from the compressed file name) and do not restore
the original time stamp if present.
• -N –name
– When compressing, always save the original file
name and time stamp
– this is the default!
gzip OPTIONS
8. • -r –recursive
– Travel the directory structure recursively
• -t –test
– Test : Check the compressed file integrity.
gzip OPTIONS
9. • -# --fast –best
– Regulate the speed of compression using the
specified digit #
• -1 or --fast
– indicates the fastest compression method
– less compression
• -9 or --best
– indicates the slowest compression method
– best compression
• The default compression level is-6
• That is, biased towards high compression at
expense of speed
gzip OPTIONS
10. gzip decompression
• Compressed files can be restored to their
original form using:
– gzip -d oror
– gunzip oror
– zcat
• gunzip can currently decompress files created
by gzip, zip, compress, compress -H or pack.
– The detection of the input format is automatic.
11. • gzip and gunzip can also compress or
decompress data from standard input and
output
– ls -laR $HOME | gzip > filelist.gz
– Or by using –c option
gzip decompression
13. bzip2
• bzip2, bunzip2
– a block-sorting file compressor, v1.0.2
• bzcat
– decompresses files to stdout
• bzip2recover
– recovers data from damaged bzip2 files
14. • on the average about 10-20% better than
gzip
– at the expense of longer compression times
• Output with .bz2 filename extension
bzip2
15. • bzip2 [ -cdfkqstvzVL123456789 ] [ filenames ... ]
• bunzip2 [ -fkvsVL ] [ filenames ... ]
• bzcat [ -s ] [ filenames ... ]
• bzip2recover filename
• Each file is replaced by a compressed version of
itself, with the name "original_name.bz2“
bzip2: SYNOPSIS
16. • -c –stdout
– (as in gzip) Compress or decompress to
standard output.
• -t –test
– Check integrity of the specified file(s), but
don't decompress them.
• This really performs a trial decompression and
throws away the result.
bzip2 OPTIONS
17. • -k –keep
– Keep (don't delete) input files during
compression or decompression.
• -s –small
– Reduce memory usage, for compression,
decompression and testing.
• -1 (or --fast) to -9 (or --best)
– Set the block size to 100 k, 200 k .. 900 k
when compressing.
– Has no effect when decompressing.
bzip2 OPTIONS
18. • bzcat
• decompresses files to stdout
• bunzip2
• Cannot use bunzip2 to uncompress files
compressed with gzip and vice versa
bzip2 decompression
19. • bzip2 -d
– decompresses all specified files.
– Files which were not created by bzip2 will be
detected and ignored
• warning issued.
bzip2 decompression
22. tar
• tar is a general-purpose archiving utility
– Stands for Tape Archive
– capable of packing many files into a single
archive file,
– while retaining information needed to restore
the files fully, such as file permissions and
ownership.
23. Tar options
• -c
– Create a new archive
• -x
– Extract files from an archive
• -t
– List table of contents to an archive
• -r
– append
24. Tar options
• -u
– Update files
• -d
– Compare files in the archive to those in the
file system
• -v
– print verbose information
• -k
– To keep any existing files when extracting
• f filename
– To specify that the tar file to be read or written is
filename.
25. • Parameter for gzip and bzip2:Parameter for gzip and bzip2:
• z
– To specify that the data to be written to the tar file should
be compressed or that the data in the tar file is compressed
with gzip.
• j
– Like z, but uses bzip2 instead of gzip;
• works only with newer versions of tar.
• Note:
– f must be the last letter in the list of options.
Tar options
26. tar
• tar saves the pathname of each file
relative to the location where the tar file
was originally created.
– tar cvf bin.tar /bin
the directory bin is created in the working
directory of tar
– You can override this behavior using the P option when packing
tar files (not recommended to do!)
