A free Basic UNIX-training with muLinux

Easy Shell Scripts

In our first dive into shell scripting, we will create some small programs, to learn some of the possibilities and advantages of shell-scripts.

A script is a text, which contains a list of commands, which are going to be interpreted by the shell. In other words, in every line of the textfile, we can write a Unix-command like ls or date. Then these will (mostly) be executed one after the other.

To save our scripts permanently, our floppy-disc needs to be mounted to /a. We create a directory with the name bin for our script-files.

/# cd /a
/a# mkdir bin
/a# cd bin
/a/bin# _

Steps to create and finish shell-scripts

1. Write the commands with a text-editor (like  vi filename ) in the Script-file.
2. The script file we gonna made into an executable file with the command  chmod u+x filename.
3. Executing the script-file is done by:  ./filename 

A small example will help review this. Firstly the scriptfile should clear the screen with: clear and then the already known command df should be executed. The script-file should be called test. By the way, you can call script-files anything you want.

/a/bin# vi test

clear df ~ ~ ~ ~ ~ ~ ~ ~ ~ "test" [New File] 2 lines, 9 chars

We save our work and leave vi:

[Esc] :wq

Now comes the second step. We need to make our file executable, so that users can run it. By using ls -l we can see that the file isn't yet an executable. If we go ...

/a/bin# chmod u+x test

The file is now executable. We can check this with ls -l:

/a/bin# ls -l test
1 -rwxr--r--  1  root root  9 Nov 17 17:59 test

The x shows us that we as a user have the permissions to execute this file. And this is what we are gonna do:

/a/bin# ./test
The output of df: all mounted devices and the
space-information on it.

The dot defines the parent working directory. We also can execute the command like this:

/a/bin# /a/bin/test

Modification of our script

[Alt] [F2]

Also there we log in as root and fire up the text editor vi:

login: root
/# cd /a/bin
/a/bin# vi test

So, now we can edit on the second console our script, save it ([Esc] :w) and change to console 1 ([Alt] [F1]) to execute it. For that we use again the repeat-command feature of Unix (Cursor-up). To continuing editing we return to console 2 ([Alt] [F2]).

Comments

Leave this blank # This is a comment-line! clear df ~ ~ ~ ~ ~ ~ ~ ~

Outputting text

# This is a comment-line! clear echo " info about the mounted devices:" df ~ ~ ~ ~ ~ ~ ~

echo Without parameters this outputs a empty line. But we can format our script to get our output a bit fancier.

# This is a comment-line! clear echo echo "info about the mounted devices:" df echo ~ ~ ~ ~ ~

Parameters

# This is a comment-line clear echo echo "info about the mounted devices:" df $* echo ~ ~ ~ ~ ~

Now we can execute our script with parameters. The parameter /a shows us the info about the mounted device mounted on mountpoint /a

/a/bin# ./test /a

The parameters /a and /tmp show us the info about the devices mounted on these mountpoints.

/a/bin# ./test /a /tmp

There can also be given special devices as parameters.

/a/bin# ./test /dev/ram0 /dev/ram1

Exercise

Hint: the floppy can't be mounted while it is being formatted! And please don't format either your work floppy or your muLinux bootdisc. And finally a copy of the error-free script should be put onto your work floppy.

So, this is it for now with shell-scripts.

To finish this lesson we unmount our work floppy.
/a# cd /
/# umount /a
/# _