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Shell Scripting Tutorial

Purpose Of This Tutorial

This tutorial is written to help people understand some of the basics of shell script programming (aka shell scripting), and hopefully to introduce some of the possibilities of simple but powerful programming available under the Bourne shell. As such, it has been written as a basis for one-on-one or group tutorials and exercises, and as a reference for subsequent use.

Getting The Most Recent Version Of This Tutorial

You are reading Version 4.5b, last updated 6th June 2023.

The most recent version of this tutorial is always available at: https://www.shellscript.sh. Always check there for the latest copy. (If you are reading this at some different address, it is probably a copy of the real site, and therefore may be out of date).

A Brief History of sh

Steve Bourne wrote the original Bourne shell which appeared in the Seventh Edition Bell Labs Research version of Unix. Many variants have come and gone over time (csh, ksh, and so on).

This tutorial restricts itself to being Bourne shell compatible, to provide a baseline. This tutorial covers all shell scripting basics. The Shell Scripting Examples section of the tutorial adds additional examples in particular of how the Bash shell provides additional useful functionality over the standard Bourne shell.

Audience

This tutorial assumes some prior experience; namely:

  • Use of an interactive Unix/Linux shell
  • Minimal programming knowledge - use of variables, functions, is useful background knowledge
  • Understanding of some Unix/Linux commands, and competence in using some of the more common ones. (ls, cp, echo, etc)
  • Programmers of ruby, perl, python, C, Pascal, or any programming language (even BASIC) who can maybe read shell scripts, but don't feel they understand exactly how they work.

You may want to review some of the feedback that this tutorial has received to see how useful you might find it.

Typographical Conventions Used in This Tutorial

Code segments and script output will be displayed as monospaced text. Command-line entries will be preceded by the Dollar sign ($). If your prompt is different, enter the command: 

PS1="$ " ; export PS1

Then your interactions should match the examples given (such as ./my-script.sh below). Script output (such as "Hello World" below) is displayed at the start of the line.

$ echo '#!/bin/sh' > my-script.sh
$ echo 'echo Hello World' >> my-script.sh
$ chmod 755 my-script.sh
$ ./my-script.sh
Hello World
$

Entire scripts will be shown with a like this, and include a reference to the plain text of the script, where available like this: my-script.sh

#!/bin/sh
# This is a comment!
echo Hello World        # This is a comment, too!

Note that to make a file executable, you must set the eXecutable bit, and for a shell script, the Readable bit must also be set. So it is likely that you will need to change the permissions on your script, to make it executable. If your script is named "myscript.sh" then you will need to change its permissions, like this: 

$ chmod u+rx myscript.sh
$ ./myscript.sh