The tar Program

• The tar program (short for tape archive) is used to create and manipulate archives containing files. These can be any kind of files (not just object code files, as with the Unix ar program). There are two main uses of tar:
  1. To bundle a collection of files together for more convenient archival. (Hence the name of the command).
  2. To bundle a collection of files together for more convenient transmission from one computer to another.
  
  
  
• An example. We assume that Myproject is a directory holding lots of files and possibly subdirectories too; README.txt is just an ordinary file. The command ...

  		tar cvf MyProject.tar README.txt MyProject 

  will create a new file whose name is MyProject.tar. This new file contains (in some format) a concatenation of all the files and directories named on the command line.
  
  (The code letters cvf are options to the tar program; tar is unusual in that a leading hyphen is not required in front of the options. It is not an error to provide a hyphen -- it is simply ignored.)
  
  The suffix .tar is not mandatory. However it is common practice and highly recommended because anyone seeing the filename MyProject.tar knows exactly what kind of file it is and how to process it.
  
  We can now e-mail or transfer the MyProject.tar file to another computer. The recipient will be able restore all the files and directories on that other computer.
  
  
• To see the names of the components of an archive file like MyProject.tar, we can execute the command:

  		tar tvf MyProject.tar 

  This outputs one line for every file or driectory, showing sizes and access permissions (much like a long ls listing).
  
  
• To retrieve one file from an archive file like MyProject.tar, we can execute a command like:

  		tar xvf MyProject.tar MyProject/main.c 

  where MyProject/main.c is the name of one of the constituent files.
  
  
• To retrieve all the files, execute:

     		tar xvf MyProject.tar 

• The meanings of some of the code letters supplied as the first command line argument tar are:

  c	create a new archive
  v	verbose output (report everything going on)
  t	produce a table of contents
  x	extract files from the archive

  
  
  
• The original purpose of tar was to backup entire disks onto magnetic tape. If a user subsequently asked for a file to be recovered from the tape, the extract option of tar would retrieve that one file.
  
  Tar is now widely used for distributing collections of related files over the internet (particularly in conjunction with compression -- see the following section).