25.Command_Aliases.md

Command Aliasing

• Alias means other alternative name or nickname.
• We can give our own more convinient nicknames for unix commands. This concept is called command aliasing.

Note: we can use type command, to check whether the command is already available or not.

How to Create Alias Names?

$ alias nickname='original command'
$ alias nickname="original command"

#  After aliasname space is not allowed. Hence the following are invalid

alias nickname ='original command'
alias nickname= 'original command'
alias nickname = 'original command'

How to List all available Aliases? By using alias command without any arguments

$ alias

How to Remove Alias Names? By using unalias command.

$ unalias alias_name

Where we can use aliasing:

1. If any lengthy command repeatedly required, then we can create shortcut alias name and we can use that short alias name every time.

alias d20f='mkdir dir1;touch dir1/file{1..20}.txt'

1. List Files and Save to Output

   • To list all files in the current working directory, save this data to output.txt, and display the number of lines to the terminal:

   alias current='ls -l | tee output.txt | wc -l'

2. Using Windows Commands in Linux

   • Create aliases for common Windows commands:

   alias cls='clear'
   alias rename='mv'

3. Correct Typing Mistakes

   • Create an alias for a common typo:

   alias grpe='grep'

4. Handle Language Barriers

   • In Germany, "datum" means "date". Create an alias for the date command:

   alias datum='date'

You can add these aliases to your .bashrc or .bash_profile file to make them permanent.

Persisting Aliases Permanently

Aliases created in a terminal session are temporary and will be lost once the terminal is closed. To make them permanent, you can use one of the following methods:

1st Way: Editing the .bashrc File

1. Open the .bashrc file in your home directory:

   gedit ~/.bashrc

2. Add your aliases to the file. For example:

   # My own aliases
   alias cls='clear'
   alias ddd='date; date; date'

3. Note: You need to close and reopen the terminal for the changes to take effect.

2nd Way: Creating a .bash_aliases File

1. Create a file named .bash_aliases in your home directory:

   gedit ~/.bash_aliases

2. Add your aliases to this file. For example:

   alias ccc='cal; cal; cal'
   alias ct='cal; date'

3. Note: Again, you must close and reopen the terminal for the changes to take effect.

FAQ

Q1: What is the Purpose of the Alias Command?
A: To list all available aliases and to create new aliases.

Q2: How to Use the Unalias Command?

• To remove a specific alias:

  unalias alias_name

• To remove all aliases:

  unalias -a

Q3: In which file do we define aliases to persist them?
A: .bashrc or .bash_aliases.

Q4: Which of the following is a valid way of creating an alias?

• A alias rename ="mv"
• B alias rename= "mv"
• C alias rename = "mv"
• D alias rename="mv"
  Answer: D
  Note: While creating aliases, do not include spaces around the = sign.