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An alias is a command in the shell that allows a word to be replaced with another string. It is mainly used to shorten system commands or provide default parameters for frequently used commands.

It is similar to a shortcut command and has the same functionality as writing an entire command.

Creating Aliases in Bash

Let’s look at an example.

$ alias update="sudo apt-get update"

We created an alias updatewhich is sudo apt-get updatea shortcut for . Now, when we run update, it works the sudo apt-get updatesame as .

$ update

Output:

[sudo] password for username: 
Get:1 https://typora.io/linux ./ InRelease [793 B]            
Get:2 http://security.ubuntu.com/ubuntu focal-security InRelease [114 kB]                                                                            
Hit:3 http://np.archive.ubuntu.com/ubuntu focal InRelease                                                                                            
Hit:4 http://ppa.launchpad.net/micahflee/ppa/ubuntu focal InRelease                                  
Ign:5 http://linux.dropbox.com/ubuntu disco InRelease                                                
Get:6 http://np.archive.ubuntu.com/ubuntu focal-updates InRelease [114 kB]                                                                           
Hit:7 http://linux.dropbox.com/ubuntu disco Release                                                                                                  
Ign:8 https://repo.mongodb.org/apt/ubuntu focal/mongodb-org/4.4 InRelease                                                                            
Hit:10 https://repo.mongodb.org/apt/ubuntu focal/mongodb-org/4.4 Release                                                                             
Get:12 http://security.ubuntu.com/ubuntu focal-security/main amd64 DEP-11 Metadata [35.7 kB]                                                         
Get:13 http://np.archive.ubuntu.com/ubuntu focal-backports InRelease [108 kB]                                                                        
Get:14 http://security.ubuntu.com/ubuntu focal-security/universe amd64 DEP-11 Metadata [66.3 kB]                                                     
Get:15 http://np.archive.ubuntu.com/ubuntu focal-updates/main amd64 DEP-11 Metadata [278 kB]                                                         
Get:16 http://security.ubuntu.com/ubuntu focal-security/multiverse amd64 DEP-11 Metadata [2,468 B]                                                   
Get:17 http://np.archive.ubuntu.com/ubuntu focal-updates/universe amd64 DEP-11 Metadata [363 kB]                                                     
Get:18 http://np.archive.ubuntu.com/ubuntu focal-updates/multiverse amd64 DEP-11 Metadata [940 B]                                                    
Get:19 http://np.archive.ubuntu.com/ubuntu focal-backports/main amd64 DEP-11 Metadata [7,996 B]                                                      
Get:20 http://np.archive.ubuntu.com/ubuntu focal-backports/universe amd64 DEP-11 Metadata [11.3 kB]                                                  
Fetched 1,102 kB in 9s (120 kB/s)                                                                                                                    
Reading package lists... Done

To list all aliases, run the following command.

$ alias

Output:

alias alert='notify-send --urgency=low -i "$([ $? = 0 ] && echo terminal || echo error)" "$(history|tail -n1|sed -e '\''s/^\s*[0-9]\+\s*//;s/[;&|]\s*alert$//'\'')"'
alias echo='show'
alias egrep='egrep --color=auto'
alias fgrep='fgrep --color=auto'
alias grep='grep --color=auto'
alias l='ls -CF'
alias la='ls -A'
alias ll='ls -alF'
alias ls='ls --color=auto'
alias show='echo'
alias update='sudo apt-get update'

The newly created alias updateis also listed with all other aliases.

Creating a Bash Alias ​​with Parameters

Bash aliases do not accept arguments directly. We have to write a function because the function mechanism is more adaptable and provides the same functionality as before.

Although an alias takes no arguments, you can call a function in the same way as an alias. Let's look at an example.

$ alias wargs='f(){ echo first "$@" last;  unset -f f; }; f'
$ wargs a b c

In the above example, a temporary function is created f. The arguments fare sent at the last call.

Unsetting -fthe option eliminates the function definition when executing the alias, ensuring that it does not linger afterwards.

Output:

first a b c last

Deleting an Alias ​​in Bash

We can use unaliasthe command to delete the alias created previously update.

$ unalias update

Let's check the list of all aliases again.

$ alias

Output:

alias alert='notify-send --urgency=low -i "$([ $? = 0 ] && echo terminal || echo error)" "$(history|tail -n1|sed -e '\''s/^\s*[0-9]\+\s*//;s/[;&|]\s*alert$//'\'')"'
alias echo='show'
alias egrep='egrep --color=auto'
alias fgrep='fgrep --color=auto'
alias grep='grep --color=auto'
alias l='ls -CF'
alias la='ls -A'
alias ll='ls -alF'
alias ls='ls --color=auto'
alias show='echo'
alias wargs='f(){ echo first "$@" last;  unset -f f; }; f'

As shown in the output, the alias updateis removed from the aliases list.