Advanced Bash−Scripting Guide

Appendix J. Copyright
The "Advanced Bash−Scripting Guide" is copyright, (c) 2000, by Mendel Cooper. This document may only
be distributed subject to the terms and conditions set forth in the Open Publication License (version 1.0 or
later), http://www.opencontent.org/openpub/. The following license options also apply.
A. Distribution of substantively modified versions of this document
is prohibited without the explicit permission of the copyright holder.
B. Distribution of the work or derivative of the work in any standard
(paper) book form is prohibited unless prior permission is obtained from
the copyright holder.
Essentially, you may freely distribute this book in unaltered electronic form. You must obtain the author's
permission to distribute a substantially modified version or derivative work. The purpose of this restriction is
to preserve the artistic integrity of this document and to prevent "forking".
These are very liberal terms, and they should not hinder any legitimate distribution or use of this book. The
author especially encourages the use of this book for instructional purposes.
The commercial print rights to this book are available. Please contact the author if interested.
The author produced this book in a manner consistent with the spirit of the LDP Manifesto.
−−−
Hyun Jin Cha has done a Korean translation of version 1.0.11 of this book. Spanish, Portuguese, French,
German, and Chinese translations are underway. If you wish to translate this document into another language,
please feel free to do so, subject to the terms stated above. The author wishes to be notified of such efforts.
Notes
[1] These are referred to as builtins, features internal to the shell.
[2] Many of the features of ksh88, and even a few from the updated ksh93 have been merged into Bash.
[3] By convention, user−written shell scripts that are Bourne shell compliant generally take a name with a
.sh extension. System scripts, such as those found in /etc/rc.d, do not follow this guideline.
[4] Some flavors of UNIX (those based on 4.2BSD) take a four−byte magic number, requiring a blank after
the !, #! /bin/sh.
[5] The #! line in a shell script will be the first thing the command interpreter (sh or bash) sees. Since this
line begins with a #, it will be correctly interpreted as a comment when the command interpreter finally
executes the script. The line has already served its purpose − calling the command interpreter.
If, in fact, the script includes an extra #! line, then bash will interpret it as a comment.
#!/bin/bash
echo "Part 1 of script."
a=1
#!/bin/bash
# This does *not* launch a new script.
Appendix J. Copyright 440