Book Image

Linux Command Line and Shell Scripting Bible - Third Edition

By : Richard Blum, Christine Bresnahan
Book Image

Linux Command Line and Shell Scripting Bible - Third Edition

By: Richard Blum, Christine Bresnahan

Overview of this book

The Linux command line enables you to type specific shell commands directly into the system to manipulate files and query system resources. Command line statements can be combined into short programs called shell scripts, a practice increasing in popularity due to its usefulness in automation. Linux is a robust system with tremendous potential, and Linux Command Line and Shell Scripting Bible opens the door to new possibilities. Linux Command Line and Shell Scripting Bible is your essential Linux guide. It contains new functional examples that are fully updated to align with the latest Linux features. Beginning with command line fundamentals, the book moves into shell scripting and shows you the practical application of commands in automating frequently performed functions. This book is a complete guide providing detailed instruction and expert advice working within this aspect of Linux. Whether used as a tutorial or as a quick reference, this book contains information that every Linux user should know.
Table of Contents (34 chapters)
2
Part I: The Linux Command Line
13
Part II: Shell Scripting Basics
20
Part III: Advanced Shell Scripting
28
Part IV: Creating Practical Scripts
32
End User License Agreement

Returning a Value

The bash shell treats functions like mini-scripts, complete with an exit status (see Chapter11). There are three different ways you can generate an exit status for your functions.

The default exit status

By default, the exit status of a function is the exit status returned by the last command in the function. After the function executes, you use the standard $? variable to determine the exit status of the function:

$ cat test4
#!/bin/bash
# testing the exit status of a function
func1() {
   echo "trying to display a non-existent file"
   ls -l badfile
}
echo "testing the function: "
func1
echo "The exit status is: $?"
$
$ ./test4
testing the function:
trying to display a non-existent file
ls: badfile: No such file or directory
The exit status is: 1
$

The exit status of the function is 1 because the last command in the function failed. However, you have no way of knowing if any of the other commands in the function completed successfully...