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

Verifying user input with lists

In this script, we will ensure that a value has been supplied to the first positional parameter. We can modify the hello2.sh script that we created in Chapter 1, What and Why of Scripting with Bash, to check for user input before displaying the hello text.

You can copy the hello2.sh script to hello4.sh or simply create a new script from scratch. There will not be a lot a typing and the script will be created as $HOME/bin/hello4.sh, as shown:

Verifying user input with lists

We can ensure that the script is executable with the following command:

$ chmod +x $HOME/bin/hello4.sh

We can then run the script with or without arguments. The test statement is looking for the $1 variable to be zero bytes. If it is, then we will not see the hello statement; otherwise it will print the Hello message. In simple terms, we will see the hello message if we supply a name.

The following screenshot shows the output that you will see when you do not supply a parameter to the script, followed by the supplied parameter...