Tar and Compress

Create a relatively large file (you can copy and paste from another). When complete, try to compress it as follows:

gzip largeFile                  

Compare the size of the compressed file and the original both in terms of bytes and allocation units. When finished, uncompress the file:

gzip –d largeFile 

Create a number of small text files (at least four) and fill them with trivial data e.g.

myFile1

myFile2

myFile3,  etc.

Try ls –ls and examine the size of each file and the number of allocation units. Now archive these files using tar.

tar cvf myFiles.tar *

Now enter ls –ls, a new file should be created. Again look at the size of the file and the number of allocation units it uses.

Finally, we can compress the new file:

gzip myFiles.tar

Do ls –ls and note .gz should be appended to the file.

Now, compare the size of the four files (i.e. the number of allocation units) and the number of allocation files taken up by the new file.

Now uncompress the tar file (gzip –d as above) and extract files from the archive:

tar xvf myFiles.tar

Exercise 1 Write a shell script which prompts a user to enter a directory path. The script should archive and compress all the files which are contained in the directory. Note: the user running the script needs to enter the full path of the directory.

Exercise 2 Write a complimentary script which de-archives and decompresses the files above. The shell should include creating a directory to contain all the de-compressed and de-archived files.

Environmental Variables

Changing PATH

Create a new directory at / e.g. /newDir

Change the directory and create a simple script (call it script1) e.g. echo “Hello”

Grant yourself permission to execute and check it runs

Return to your home directory and try to run it again – it should not run.

Now add the directory (i.e. /newDir) to your PATH e.g. PATH=$PATH:/newDir and try again.

It should work from any directory (don’t use ./ with it), enter script1.

Making PATH permanent

Unfortunately when you change PATH from the command line (as above) means only a temporary change.

To make the change permanent, create the file .bash_profile (if it’s not already there) in your home directory.

           

PATH=$PATH:/newDir

            export PATH

Once the file is saved, log out and log in again. The script should now run.

PS1 – the primary prompt

Set PS1=”Hello Everybody”

To make it permanent, create .bashrc

PS1=”My Linux: “

export PS1

Exercise 3 – look up to see how prompt colours can be changed.