1. The Korn Shell Environment
2. Standard Files and Special Operators
3. Using Aliases
4. Shell Variables and Functions
5. What is a Shell Script?
6. Writing a Basic Shell Script
7. Advanced Shell Scripting
   

The Korn Shell Environment

Just as Windows is the world-recognized operating system interface to the majority of PC's in use today, the shell is the standard interface to UNIX and Linux operating systems. When you log on, the shell prompt represents your first opportunity to issue commands directly to the operating system.

While the shell prompt displayed differs depending on the type of shell invoked - $ and % prompts are displayed for Bourne and C shells, respectively - the Korn shell (also a $ prompt) is the most powerful, widely used shell in today's environments. This course focuses exclusively on the scripting capabilities available in the Korn shell.

- What is a Korn Shell?
- Starting up a Korn Shell
- Basic shell behavior

Standard Files and Special Operators

While the Korn shell is a powerful, versatile tool that is indispensable in communicating with the operating system, it was written from a programmer's perspective - therefore, it is not intended to serve as a high-level, user-friendly interface. It functions according to explicit commands and shows little tolerance for the uninitiated. Therefore, it is important to be familiar with the basic rules that give the shell its unique character.

- How the Korn Shell sees things
- Pattern matching and standard metacharacters
- Recalling and modifying commands
- Redirects, pipes, and input/output operators
- Redirects, pipes, and input/output operators (appending and pipes)
- Command substitution
- Using grep
- Using grep (metacharacters and pipes)
- Basic filters

Using Aliases

In the Korn shell, aliases are synonyms for longer commands. Or, in other words, they are miniature shell scripts that are stored in the working memory of the shell instead of a file. Aliases are probably the most widely used way of customizing your environment to save typing and give more recognizable names to complex commands.

- Making aliases
- Listing aliases
- Removing aliases

Shell Variables and Functions

A key to basic shell scripting is the ability of the Korn shell to combine standard commands with user-defined data to create more efficient, customized tools. In addition to command substitution and aliases, the Korn shell supports shell variables and functions that behave in similar, but more powerful ways.

- Shell variables
- Shell variables (displaying, changing, deleting)
- Shell variables (substitution, protection, combining)
- Functions
- Creating functions

What is a Shell Script?

A shell script is merely an executable file containing multiple shell commands that are executed sequentially. The file can contain:

· a shell definition statement
· comments
· commands

The Korn shell supports a number of features and functions that make learning shell scripting techniques preferable to learning a standard programming language such as C or C++. An added bonus of using a shell script is that it is interpreted, meaning that it does not have to be compiled like most programming languages.

- An overview
- Shell script execution
- Shell scripts - an illustrated view

Writing a Basic Shell Script

In previous modules, we covered a lot - if not most - of the shell features and commands that might be used in a basic shell script. We also touched briefly on some rules that well-written shell scripts should follow. In this module, we'll get more detailed about the proper construct of a good shell script and also show some other ways that scripts receive and interpret data. At the very end, we'll put those things to use in building a shell script that you can execute on the lab system.

- What's in a shell script
- Conditionally executing commands in a shell script
- Passing information to a shell script using positional parameters
- Using the read command
- Interactively passing variables to the read command
- Flow control and looping commands (while and case)
- Flow control and looping commands (exit and break)
- Flow control and looping commands (select)
- Putting it all together (menu script #1)
- Putting it all together (menu script #2)

Advanced Shell Scripting

The final module of the course discusses Korn shell scripting tools used by more advanced script writers. Again, it would impossible to cover everything that is available as a resource for script writers using the Korn shell, but the things discussed in this module show up often in intermediate-to-complex scripts.

- Looping and logic
- Looping and logic (if, if-else, and elif)
- More flow control and looping statements (for and until)
- More flow control and looping statements (continue and nested loops)
- Scheduling automatic script execution with the cron program
- Using escape characters with the print command
- Error checking and debugging your shell scripts
- Arithmetic operators
- The ((...)) command