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

Awk control files


Just as with sed, we can simplify the command line by creating and including control files. This also makes the later editing of the command more easily achievable. The control files contain all the statements that we want awk to execute. The main thing that we must consider with sed, awk, and, shell scripts is modularization; creating reusable elements that can be used to isolate and reuse the codes. This saves us time and work and we get more time for the tasks that we enjoy.

To see an example of an awk control file, we should revisit the formatting of the passwd file. Creating the following file will encapsulate the awk statements:

function green(s) {
    printf "\033[1;32m" s "\033[0m\n"
}
BEGIN {
    FS=":"
    green("   Name:   UID:       Shell:")
}
{
    printf "%10s %4d %17s\n",$1,$3,$7
}

We can save this file as passwd.awk.

Being able to encompass all the awk statements in the one file is very convenient and the execution becomes clean and tidy:

$ awk -f passwd.awk...