Using 'tar' (file archive) and 'gzip' (file compression) 




  










Available CEE UCL softeware(s) related to this topic:



    

  • tar (command-line mode)

  • xtar (X11)

  • gzip (command-line mode)

  • compress/uncompress (command-line mode)

  • zip/unzip (command-line mode)

  • lha (command-line mode)









When a big file(s) or directory(ies) is not used frequently 
but you still need to keep it in your account for future use, 
you may consider compressing it or archiving it or 
both to conserve disk space.  



There are several common tools for archiving and compressing; "tar", "compress/uncompress",
"gunzip(=gzip) " and "zip/unzip".



The "tar" (tape archiver) command is useful for 
storing or "archiving" a bunch of files and directories.  
It archives and extracts files to and from a single file 
called a "tarfile. "  The "tape" in tar command originated 
from the "old days" when backup and archive were solely 
done using magnetic tape devices, but it doesn't have 
to be nowadays and it can be any file.  (well, still 
tape backup is the most common means to do regular system backups).



The syntax for "tar" command is





$ tar  [key]  [name ...]





where key is specified by a plethora of options (see abridged list below
and unabridged list in the man
pages) and name is either the file name or device name (such as magnetic
tapes, CD-R, WORM, MO disk, etc.). Here are some of the more commonly
used keys:











	tar key
	It will


	c
	Creates a new tape


	t
	Lists the contents of a tarfile without untarring a tarfile


	f
	File.  Use the [name] argument as the name 
		of the tarfile instead of the default tape device.


	v
	Turns verification on


	x
	Extracts selected files.  If no file argument 
		is given the entire contents of the tar 
		file is extracted











Here is some examples:





$ tar  cvf  oink.tar  /home/wclinton/project




Create a tarfile that archives all files and subdirectories 
in "/home/wclinton"







$ tar  tvf  /dev/rmt0/jumbo.tar




List contents of a tarfile in a magnetic tape ("/dev/rmt0" 
is a standard name for a mounted tape drive)








$ tar  xvfp  ~/archive/noway.tar  ~/project




Extract all files from "noway.tar" tarfile in 
"/home/wclinton/archive" directory to "/home/wclinton/project" 
directory.  If "noway.tar" tarfile contains subdirectoies, 
they'll be also extracted under "/home/wclinton/project" 
directory.








It is a common practice to compress the resulting tarfile when archiving
(=tarring) is completed. Compression is done by using either "gunzip
(=gzip) " or "compress"
command. 





$ gzip  -9  oink.tar




Compress "oink.tar" using gzip with a maximum compression.
Resulting file will be "oink.tar.gz"








$ compress  oink.tar




Compress "oink.tar" using compress command. Resulting file 
will be "oink.tar.Z"






"gzip" is better in compression speed and efficiency 
than "compress."  However, "compress" is a standard command 
comes with the Unix OS, whereas "gzip" is a GNU program 
you need to install.



Thus, if you're preparing a "gzipped 
tarfile" file(s) for others, make sure the person who will 
receive the "gzipped & tar'd " file" (or often called as 
"tarball")
has "gzip" installed in 
one's system. (if not sure, use "compress" instead)



Now, here's how to uncompress and untar (=extract) a 
compressed and tarred archive.  Here, I'm using the 
pipeline technique that we discussed previously.





$ gzip  -cd  oink.tar.gz  | tar  xpvf  -




Decompress and extract all files/directories from 
"oink.tar.gz" to current directory








$ uncompress  oink.tar.Z  | tar  xpvf  -




Decompress and extract all files/directories from 
"oink.tar.Z" to current directory






Further details on "compress" can be found from man
pages. For "gzip," type "gzip -h" for additional flags information.



zip/unzip compression method popular
in wintel PCs is also available via "zip/unzip" command. Their usage and
flags information can be also found by typing "zip -h" and "unzip -h."