Bash-Beginners-Guide

Bash Guide for Beginners
rbash script_name.sh
sh script_name.sh
bash -x script_name.sh
The specified shell will start as a subshell of your current shell and execute the script. This is done when you
want the script to start up with specific options or under specific conditions which are not specified in the
script.
If you don't want to start a new shell but execute the script in the current shell, you source it:
source script_name.sh
source = .
The Bash source built-in is a synonym for the Bourne shell . (dot) command.
The script does not need execute permission in this case. Commands are executed in the current shell context,
so any changes made to your environment will be visible when the script finishes execution:
willy:~/scripts> source script1.sh
--output ommitted--
willy:~/scripts> echo $VALUE
9
willy:~/scripts>
2.2. Script basics
2.2.1. Which shell will run the script?
When running a script in a subshell, you should define which shell should run the script. The shell type in
which you wrote the script might not be the default on your system, so commands you entered might result in
errors when executed by the wrong shell.
The first line of the script determines the shell to start. The first two characters of the first line should be #!,
then follows the path to the shell that should interpret the commands that follow. Blank lines are also
considered to be lines, so don't start your script with an empty line.
For the purpose of this course, all scripts will start with the line
#!/bin/bash
As noted before, this implies that the Bash executable can be found in /bin.
2.2.2. Adding comments
You should be aware of the fact that you might not be the only person reading your code. A lot of users and
system administrators run scripts that were written by other people. If they want to see how you did it,
comments are useful to enlighten the reader.
Chapter 2. Writing and debugging scripts 24