Department of Statistics

University of Illinois at Urbana-Champaign

TAR - Tape ARchive

A tar file is a collection of files. In its most basic use, the tar command adds files to a tar file or extracts files from a tar file. The tar command is so useful because you can easily move tarfiles around. Altough the name tar (which comes from Tape Archive) refers to a tape, you don't need to use a tape. A tar file conventionally ends with a .tar suffix.

Format

tar [flags] [the location or name of the tar file] [files to add or extract]

Flags

• c - create - create a new tar file (and put files into it)
• x - extract - extract files from the tar file
• u - update - add files to an already existing tar file
• v - verbose - output information on what files are being manipulated
• t - table of contents - list the names of files within the tar file
• f - file - use a file instead of a tape (very common)

Examples

• Simple Examples of tarfile Creating, Updating, and Extracting

  1. Create a tarfile

     ux6> tar -cvf tarfile.tar readme.txt stat100 stat410
     readme.txt
     stat100/
     stat100/hw1.txt
     stat410/
     stat410/hw1.txt
     

  2. Update a tarfile

     ux6> tar -uvf tarfile.tar newfile.txt
     newfile.txt
     

  3. Extract a tarfile

     ux6> tar -xvf regress.tar
     regress/
     regress/readme.txt
     regress/somefile.c
     regress/anotherfile
     regress/updates
     

• Using tar to move multiple files between systems

  If I want to move all my files in my stat100 directory on ux6 to ux1, I could use ftp to transfer each file individually, but it would be must faster to
  1. Create a tarfile on ux6
  2. Use ftp to transfer that tar file to ux1
  3. Extract the tar file on ux1
  In this example, my home directory has only a few files. There is a directory called stat100, and in the stat100 directory there are a few files as well as a directory called old. I create a tar file called myfile.tar.

  ux6> cd
  ux6> ls  
  chem210    mbox       reminder   stat100    stat452    test
  
  ux6> tar -cvf mytarfile.tar stat100 

  note the flags

  stat100/
  stat100/dataset
  stat100/old/
  stat100/old/hw1.txt
  stat100/old/notes.txt
  stat100/hw1.txt
  stat100/hw2.txt
  stat100/hw3.txt
  
  ux6> ftp ux1
  [login]
  ftp> bin
  ftp> put mytarfile.tar
  ftp> quit
  
  ux6> telnet ux1
  
  [login]
  
  ux1> ls
  mbox 	mytarfile.tar
  ux1> tar -xvf mytarfile.tar
  stat100/
  stat100/dataset
  stat100/old/
  stat100/old/hw1.txt
  stat100/old/notes.txt
  stat100/hw1.txt
  stat100/hw2.txt
  stat100/hw3.txt
  
  ux1> ls
  mbox	stat100		mytarfile.tar
  

• Using ls and cat to create a list of files to include in a tarfile

  1. Use ls -ap to get a listing of all the files in a directory.
     • The a flag will force listing off all files, including files with a . prefix.
     • The p will add a / after the name of a directory.
  2. Use the > redirector to send the output of the ls into a new file.
  3. Edit this new file. Be sure to remove the entry for the parent and current directory (./ and ../), otherwise you'll run into a mess. Be aware that if you include the name of a directory, tar will include all the files within that directory.
  4. Instead of supplying a list of files as usual with tar -cvf, use the cat command within a set of backticks (`) as follows:`cat filename`.

  ux6> c
  ux6> ls -a > filelist
  ux6> [edit filelist as above]
  ux6> tar -cvf newtarfile.tar `cat filelist`
  

Gotchas & Common Mistakes

• Inadvertently overwriting files.

  If there is a file in a tarfile with the same name as an existing file, the file in the tarfile will overwrite without notice the existing file. This can be a problem if you are extracting all the files from one system to another system (for example, many systems will have the file mbox for old mail).

  One way to avoid this problem: Create a temporary directory which you extract the tar file into. Then you can use cp or mv to re-organize your files.

• Infinite loop tarfiles.

  Be sure that when you create or update a tarfile, you do not add the tarfile back into itself. This will cause an infinite loop and eventually take up all the available disk space on the system. Here is a sad example of what NOT TO DO to make a tarfile that would contain all the files in your home directory:

  ux6> cd
  ux6> tar -cvf newtarfile.tar .
  

  All the files in your home directory will be added to the file newtarfile.tar. This is a good start, but now the file newtarfile.tar is also in your home directory, so the tar process will try to add the file newtarfile.tar to itself. Newer versions of tar will prevent you from doing this.

  Be sure that the location of your new tarfile is not in the path of the files you are adding to the new tarfile. /tmp is one possibile location, but may not be too secure.

• Rootless tarfiles.

  Sometimes you will find (or create!) tarfiles that do not have a beginning directory. I find it useful to group files in a rooted directory, so when someone extracts the tarfile, the files will have a little organization and will not just spill all over the current directory.
  • If you use the symbol for "the current directory" (a dot), for the list of files you want to include in a tar file, you will end up with a rootless tarfile:

    ux6> cd
    ux6> cd furniture
    ux6> tar -cvf /tmp/furniture.tar .
    ./
    desk
    chair
    table
    

  • You can avoid rootless tar files by issuing the tar command from the parent directory.

    ux6> cd 
    ux6> cd furniture
    ux6> cd ..
    ux6> tar -cvf furniture.tar furniture
    furniture/
    furniture/desk
    furniture/chair
    furniture/table
    

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Last Updated 4/2/97

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