1. Unix Scripting
Session 1
March 6, 2008

2. A Very Brief History of Unix
Invented in late 1960s at AT&T Bell Labs
They were not allowed to sell it, so they licensed it to places like Berkeley, starting with Version 6
Version 7 was the first widely-known version of Unix, incorporating both Bell Labs and Berkeley innovations
The 1984 break-up of AT&T allowed it to be sold for commercial purposes

3. Diverging Paths
Berkeley’s version became known as the Berkeley Standard Distribution, or BSD, and led to 4.2, 4.3, and 4.4 releases among others
AT&T marketed System III, based on Version 7, then later System V, which was a success especially on AT&T 3B series computers
Sun Microsystems originally based SunOS on BSD, then joined with AT&T to create SVR4, the core of which became Solaris 2.x

4. Who Cares?
Why is the fact that there are multiple versions of Unix important?
Because each brought unique tools to the core operating system, leading to many choices to solve problems
“There’s more than one right way to do it”

5. The Shell
A command line interface in Unix is called a “shell”, and can be used both interactively and for scripting
The default shell is /bin/sh, first the Thompson Shell then later the Bourne Shell (v7)
The Bourne Shell is the most portable shell, and will be found on all dialects of Unix
Easy to program, not friendly interactively

6. The C Shell
The C Shell (csh) was written by Bill Joy for BSD (he also wrote vi, NFS, and other things)
Syntax based on C, hence the name
Much friendlier for interactive use, includes history substitution, aliases and job control
Scripting syntax can be ambiguous and confusing, aliases can cause unexpected results
Not found on all dialects of Unix

7. Other Shells
The Korn Shell (ksh), an enhanced Bourne Shell with many C Shell features plus history editing and enhanced scripting features
The Tenex C Shell (tcsh), an enhanced C Shell with history editing and enhanced syntax
The Bourne-Again Shell (bash), part of the GNU project and the default /bin/sh on Linux systems, very similar to the Korn Shell

8. What is a Shell Script?
A script is a text file containing commands to be executed by a scripting language
A shell script specifically uses a shell
Scripts must be executable: chmod +x script
The shebang (also called a “pound bang”) tells the operating system which shell to use:
#!bin/sh
#!/bin/csh
#!/bin/ksh

9. Other Scripting Languages
Scripting is not just for shells
Scripts can be written in awk, sed, and other common Unix utilities
Popular add-on scripting languages include Perl, Tcl/Tk, Python, and Ruby
Shebangs are used for these as well:
#!/usr/bin/awk
#!/util/perl/bin/perl

10. Which Ones to Use? For shell scripting, we use the Bourne Shell:
Simple
Portable
Easy for running Unix commands
For other scripting needs, we use Perl:
As simple or complex as you want it to be
Becoming standard on newer versions of Unix
Great for text manipulation and systems programming

11. Our First Bourne Shell Script
#!/bin/sh echo "Hello, world!" for number in ; do echo "$number…\c" done echo "Liftoff!" exit 0

12. References The Creation of the Unix Operating System:
Unix Seventh Edition Manual:
Dennis Ritchie's Home Page:
The Bourne Shell:
The C Shell (Read external links):