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 (16 chapters)
15
Index

Creating conditional statements using if

As we have seen so far, it is possible to build simple conditions using command-line lists. These conditionals can be written both with and without a test. As the complexity of the tasks increases, it will be easier to create statements using if. This certainly will ease both the readability of the script and the logic layout. To a degree, it also matches the way in which we think and speak, if is a semantic in our spoken language as it is within the bash script.

Even though it will take up more than a single line in the script, with an if statement we can achieve more and make the script more legible. With that said, let's look at creating if conditions. The following is an example of a script using an if statement:

#!/bin/bash
# Welcome script to display a message to users
# Author: @theurbanpenguin
# Date: 1/1/1971
if [ $# -lt 1 ] ; then
echo "Usage: $0 <name>"
exit 1
fi
echo "Hello $1"
exit 0

The code within the if...