In the Linux system, alias commands are a very useful feature that allows users to define simplified commands to execute complex operations. Sometimes, users may need to cancel previously set alias commands in order to use the original commands or change them to new aliases. This article will provide detailed instructions on how to cancel alias commands in the Linux system, including temporary cancellation and permanent cancellation methods, with specific examples.

Temporary Cancellation of Alias Commands

The temporary cancellation of alias commands is relatively simple. You just need to use the unalias command or add a backslash before the command in the session where you need to use the original command.

Using the unalias command

The unalias command is used to temporarily cancel a previously set alias. The syntax of this command is as follows:

unalias alias_name

If you have an alias called lsa, which is set to ls la, you can use the following command to temporarily cancel this alias:

unalias lsa

In this session, the lsa alias will be canceled, and you can use the original ls la command. However, please note that this cancellation is temporary and the alias will be restored when the session ends or after re-logging in.

Using a backslash (\\)

Another method of temporarily canceling an alias is to add a backslash before the command in the place where you want to use the original command. This tells the shell to ignore any alias and execute the original command directly.

If you have an alias called ll, which is set to ls l, you can use the following command to temporarily cancel this alias:

\ll

This will execute the original ls l command instead of the ll alias. Similarly, this cancellation is also temporary and only valid for the current session.

Permanent Cancellation of Alias Commands

Permanent cancellation of alias commands requires editing the alias configuration file, which is usually either ~/.bashrc or ~/.bash_profile. Here are the specific steps:

1. Open a terminal.

2. Open the alias configuration file using a text editor. For the ~/.bashrc file, you can use the following command:

nano ~/.bashrc

3. In the opened file, find the alias definition line that needs to be canceled. It usually looks like this:

alias alias_name='original_command'

4. Delete or comment out the line (add a # at the beginning).

5. Save and close the file.

6. To make the changes take effect, you need to reload the configuration file. You can use the following command:

source ~/.bashrc

or

. ~/.bashrc

7. Now, the alias has been permanently canceled, and you can use the original command in any new session.

Example

Suppose you have an alias called grep, which actually executes grep color=auto. If you want to cancel this alias to use the grep command without the color option in certain cases, you can permanently cancel this alias by following the steps mentioned above.

Related FAQs

Q1: What should I do if I don't know where the alias is set?

A1: You can use the alias command to list all aliases in the current session. If you want to see the permanently set aliases, you can check the ~/.bashrc, ~/.bash_profile, or /etc/profile.d/ files. Usually, user-defined aliases are set in the ~/.bashrc or ~/.bash_profile file.

Q2: Can I create an alias to cancel another alias?

A2: Yes, you can create an alias that cancels another alias. Let's say you have an alias ll, and you want to create a new alias original_ll to execute the original ls l command. You can define it as follows:

alias original_ll='ls l'

This way, when you use original_ll, it will execute the original ls l command instead of the ll alias. However, please note that this method only temporarily cancels the alias, as it relies on the alias definition in the current session.

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