Tar Tutorial

Prerequisites

Step 1 -- Create a directory to work with and download a "tarball"

Start off with the following:

$ mkdir TarTutorial
$ cd TarTutorial
$ wget http://www.mmm.ucar.edu/wrf/src/WRFDAV3.1.tar.gz
$ ls -ltr

The third command will take a while because it is downloading a file from the internet. The file is call a "tarball" or a "gzipped tarball". TAR is an old unix short name for "tape archive" but a tar file is a file that contains a bunch of other files. If you have to move a bunch of files from one place to another, a good way to do it is to pack them into a tar file, move the tar file where you want it then unpack the files at the destination. A tar file usually has the extension ".tar". What about the ".gz"? This means the tar file has been further compressed with the program gzip -- this makes it a lot smaller.

Step 2 -- Unpack the "tarball" and check out the contents

After step 1 your working directory should be ~/TarTutorial and there should be a file called WRFDAV3.1.tar.gz in it.

Now do this:

$ gunzip WRFDAV3.1.tar.gz
$ ls -ltr

You should now have a file called WRFDAV3.1.tar which should be quite a bit larger in size than WRFDAV3.1.tar.gz -- this is because it has been uncompressed by the "gunzip" command which is the opposite of the "gzip" command.

Now do this:

$ tar -xvf WRFDAV3.1.tar
$ ls -ltr

You should see a lot of filenames go by on the screen and when the first command is done and you issue the ls command you should see two things -- WRFDAV3.1.tar is still there but there is also a directory called WRFDA. You can look at the contents of this directory and navigate around in the directory tree to see what is in there. The options on the "tar" command have the following meanings (you can do a "man tar" to get all the options):

x: extract the contents of the tar file

v: be verbose, i.e. show what is happening on the screen

f: the name of the file which follows the "f" option is the tar file to expand.

Another thing you can do is see how much space is being taken up by the files. Make sure TarTutorial is your working directory then issue the following command:

$ du .

Remember that "." (dot) means the current working directory. The "du" command means "disk usage" -- it shows you how much space is being used by every file and directory in the directory tree. It ends up with the highest level files and directories. You might prefer to do

$ du -h .
$ ls -ltrh

Adding the "-h" option to these commands puts the file sizes in human-readable format -- you should get a size of 66M for the tar file -- that's 66 megabytes -- and "du" should print a size of 77M next to ./WRFDA.

Step 3 -- create your own "tarball"

Now, make your own tar file from the WRFDA directory tree:

$ tar -cf mywrf.tar WRFDA
$ ls -ltrh

You have created a tar from all the files in the WRFDA directory. The options given to the "tar" command have the following meanings:

c: create a tar file

f: give it the name which follows the "f" option

The files WRFDAV3.1.tar and mywrf.tar are identical. Now compress the tar file you made:

$ gzip mywrf.tar
$ ls -ltrh

You should see a file called mywrf.tar.gz which is smaller than WRFDAV3.1.tar.

Step 4 -- Clean up!

You don't want to leave all these files lying around. So delete them

$ rm WRFDAV3.1.tar
$ rm mywrf.tar
$ rm WRFDA

Oops! You can't remove the directory. You need to use the "rmdir" command:

$ rmdir WRFDA

Oh no! That doesn't work on a directory that's not empty. So are you stuck with all those files? Maybe you can do this:

$ cd WRFDA
$ rm *
$ cd ..
$ rmdir WRFDA

That won't work either because there are some subdirectories in WRFDA and "rm *" won't remove them. Do you have to work your way to the all the leaves at the bottom of the directory tree and remove files then come back up and remove directories? No, there is a simpler way:

$ rm -Rf WRFDA

This will get rid of the entire directory tree. The options have the following meanings:

R: recursively remove all files and directories

f: force; i.e., just remove everything without asking for confirmation

I encourage you to do

$ man rm

and check out all the options. Or some of them -- there are quite a few.