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

Script comments


We should always introduce commenting scripts early in the piece. A script comment is prefaced with a # symbol. Anything after the # symbol is a comment and is not evaluated by the script. The shebang, #!/bin/bash, is primarily a comment and, as such, is not evaluated by the script. The shell running the script reads the shebang so it knows which command interpreter to hand the script over to. A comment may be at the start of a line or partly into the line. Shell scripting does not have the notion of multi-line comments.

If you are not already familiar with comments, then they are added to the script to tell all about who wrote the script, when it was written and last updated, and what the script does. It is the metadata of the script.

The following is an example of comments in scripts:

#!/bin/bash
# Welcome script to display a message to users on login
# Author: @theurbanpenguin
# Date: 1/1/1971

It is a good practice to comment and add comments that explain what the code is...