Shell Scripts

Overview

#!/bin/bash
#!/usr/bin/env python
#!/bin/csh
#!/usr/bin/perl

Since you need to execute the shell script, you need execute permission on the file.
Remember that chmod is how you change permissions.
You can also "sh" the script - for instance, run: bash filename
Since the bash command interprets the commands in your script, you must have read permission on the file.

Think more about permissions: Do you need execute permission on the file when sh-ing the script? If you have execute and can just run it, do you also need read permission?

To execute the script directly, the file must also be in your PATH - we will set this up during class time.
If it is not, then you must give the path of the file rather than just use the command name.
There are a number of commands that will tell you where a command is located: which whence whereis type

REMINDER: Which ones are on your system?

There are special scripts that are meant to set up your environment - to run these you must "dot" them: . command
Your profile is an example of this type of script and we will look at it together.

We will start writing some shell scripts as we go through the material, so let's get set up now:

Under your HOME directory, create a directory called cmd.
cd to that directory and do your work from there.
Create a file called myll that has the command to do a long listing in the current directory.
Change its permissions to 755.
Execute it.
Go home and execute it twice, once with a relative path and once with an absolute path.

Shell Programming Syntax

Note: Shell has many standard programming constructs, like ifs, loops, functions, arguments, ... I will post notes on these, but we will focus on the basics. To learn about all possibilities, read the man page for bash (or whatever flavor of LINUX you are interested in).

Basic Syntax				More Advanced Syntax

Arguments if Logical Expressions				for while Functions Basic Math

Lets Write Some Shell Scripts