Book Image

Mastering Linux Shell Scripting

By : Andrew Mallett
Book Image

Mastering Linux Shell Scripting

By: Andrew Mallett

Overview of this book

Shell scripting is a quick method to prototype a complex application or a problem by automating tasks when working on Linux-based systems. Using both simple one-line commands and command sequences complex problems can be solved with ease, from text processing to backing up sysadmin tools. In this book, you’ll discover everything you need to know to master shell scripting and make informed choices about the elements you employ. Get to grips with the fundamentals of creating and running a script in normal mode, and in debug mode. Learn about various conditional statements' code snippets, and realize the power of repetition and loops in your shell script. Implement functions and edit files using the Stream Editor, script in Perl, program in Python – as well as complete coverage of other scripting languages to ensure you can choose the best tool for your project.
Table of Contents (21 chapters)
Mastering Linux Shell Scripting
About the Author
About the Reviewer

Conditional statements in Perl

Similar to the rest of the Perl language, we will have similarities with bash scripting and some completely new ways of implementing conditions. This will often work in our favor; thus, making the code more readable.

Replacing command line lists

First, we do not have the command line list logic, which we use in bash and we do not make use of the && and ||. Instead of these rather weird looking symbols, the conditional logic for single statements in Perl is written in the following manner:

exit(2) if scalar @ARGV < 1;
print("Hello $ARGV[0]\n") unless scalar @ARGV == 0;

In the first example, we exit with an error code of 2, if we have supplied less than one command-line argument. The bash equivalent to this will be:

[ $# -lt 1 ] && exit 2

In the second example, we will only print the hello statement if we have supplied arguments. This will be written in bash, as shown in the following example:

[ $# -eq 0 ] || echo "Hello $1"

Personally, I like Perl...