Book Image

Linux Shell Scripting Cookbook, Second Edition - Second Edition

Book Image

Linux Shell Scripting Cookbook, Second Edition - Second Edition

Overview of this book

The shell remains one of the most powerful tools on a computer system — yet a large number of users are unaware of how much one can accomplish with it. Using a combination of simple commands, we will see how to solve complex problems in day to day computer usage.Linux Shell Scripting Cookbook, Second Edition will take you through useful real-world recipes designed to make your daily life easy when working with the shell. The book shows the reader how to effectively use the shell to accomplish complex tasks with ease.The book discusses basics of using the shell, general commands and proceeds to show the reader how to use them to perform complex tasks with ease.Starting with the basics of the shell, we will learn simple commands with their usages allowing us to perform operations on files of different kind. The book then proceeds to explain text processing, web interaction and concludes with backups, monitoring and other sysadmin tasks.Linux Shell Scripting Cookbook, Second Edition serves as an excellent guide to solving day to day problems using the shell and few powerful commands together to create solutions.
Table of Contents (16 chapters)
Linux Shell Scripting Cookbook
About the Authors
About the Reviewers

Visiting aliases

An alias is basically a shortcut that takes the place of typing a long-command sequence. In this recipe, we will see how to create aliases using the alias command.

How to do it...

There are various operations you can perform on aliases, these are as follows:

  1. An alias can be created as follows:

    $ alias new_command='command sequence'

    Giving a shortcut to the install command, apt-get install, can be done as follows:

    $ alias install='sudo apt-get install'

    Therefore, we can use install pidgin instead of sudo apt-get install pidgin.

  2. The alias command is temporary; aliasing exists until we close the current terminal only. To keep these shortcuts permanent, add this statement to the ~/.bashrc file. Commands in ~/.bashrc are always executed when a new shell process is spawned:

    $ echo 'alias cmd="command seq"' >> ~/.bashrc
  3. To remove an alias, remove its entry from ~/.bashrc (if any) or use the unalias command. Alternatively, alias example= should unset the alias named example.

  4. As an example, we can create an alias for rm so that it will delete the original and keep a copy in a backup directory:

    alias rm='cp $@ ~/backup && rm $@'


When you create an alias, if the item being aliased already exists, it will be replaced by this newly aliased command for that user.

There's more...

There are situations when aliasing can also be a security breach. See how to identify them.

Escaping aliases

The alias command can be used to alias any important command, and you may not always want to run the command using the alias. We can ignore any aliases currently defined by escaping the command we want to run. For example:

$ \command

The \ character escapes the command, running it without any aliased changes. While running privileged commands on an untrusted environment, it is always good security practice to ignore aliases by prefixing the command with \. The attacker might have aliased the privileged command with his/her own custom command to steal the critical information that is provided by the user to the command.