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Linux Shell Scripting Essentials

Linux Shell Scripting Essentials

By : Sinny Kumari
4.5 (2)
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Linux Shell Scripting Essentials

Linux Shell Scripting Essentials

4.5 (2)
By: Sinny Kumari

Overview of this book

Shell scripting is a quick method to prototype complex applications or problems. Shell scripts are a collection of commands to automate tasks, usually those for which the user has a repeated need, when working on Linux-based systems. Using simple commands or a combination of them in a shell can solve complex problems easily. This book starts with the basics, including essential commands that can be executed on Linux systems to perform tasks within a few nanoseconds. You’ll learn to use outputs from commands and transform them to show the data you require. Discover how to write shell scripts easily, execute script files, debug, and handle errors. Next, you’ll explore environment variables in shell programming and learn how to customize them and add a new environment. Finally, the book walks you through processes and how these interact with your shell scripts, along with how to use scripts to automate tasks and how to embed other languages and execute them.
Table of Contents (10 chapters)
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9
Index

Managing the crontab entry


We don't add or modify an entry of a crontab directly. It is done by using the crontab command that allows you to add, modify, and list crontab entries. Each user can have their own crontab where they can add, delete, or modify tasks. By default, it is enabled for all users, but if a system administrator wants to restrict some of the users, he or she can add that user in the /etc/cron.deny file.

The syntax of using the crontab command is as follows:

crontab [-u user] file
crontab [-u user] [option]

The options of the crontab are explained in the following table:

Option

Description

-u user

Appends the name of the user whose crontab is to be modified

-l

Displays the current crontab on stdout

-e

Edit the current crontab using an editor specified by the EDITOR env

-r

Remove the current crontab

-i

Interactive removal of the current crontab when used with the -r option

Listing crontab entries

To list the crontab entries, we use the -l option for...

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