Linux · system information

alias

a shortcut for a command

alias gives a command a nickname. Type the short name and the shell replaces it with the full command. An alias lasts only for the current shell unless it is written into ~/.bashrc.

If you type it ten times a day, give it a two-letter name.

Define

alias ll='ls -la'

no spaces around the =

List

alias

with no arguments

Remove

unalias ll

for this shell

Keep it

~/.bashrc

read at every new shell

At the terminal

Read the session first, then the notes: each numbered line in the output is answered by the note with the same number.

user@netflow — bashbash

$ alias

1alias grep='grep --color=auto'

alias ll='ls -alF'

2$ alias gs='git status'

3$ type ll

ll is aliased to `ls -alF'

4$ echo "alias gs='git status'" >> ~/.bashrc

Illustrative session · names, sizes and dates are examples, and every address is from a documentation or private range

Reading the output

What the numbered lines are telling you

Aliases you already have

Most distributions define a few. This is why grep shows colour and ll works without you having set anything up.

Defining one

From now on, in this shell, gs runs git status. Quote the command so the spaces are kept together.

type shows what a name means

It reports that ll is an alias and what it expands to.

Making it permanent

Appending the line to ~/.bashrc defines the alias in every new shell. Run "source ~/.bashrc" to load it now.

Switches

A switch changes how the command behaves. These are the ones used day to day; man alias lists the rest. Single-letter switches can usually be joined, so -l -a may be written -la.

-p: Print all aliases in a form that can be reused as input.

Variations worth knowing

The same tool, pointed at a narrower question. These four cover most of what it is reached for day to day.

alias rm='rm -i'

Makes rm ask before each removal.

\ls

A leading backslash runs the real command, ignoring any alias.

unalias -a

Removes every alias from the current shell.

alias ports='ss -tulpn'

A memorable name for a command with awkward switches.

In cybersecurity

An alias means the command you type may not be the command that runs.

A hijacked alias

Someone with write access to your .bashrc can alias sudo to a script that records your password and then runs the real sudo. Check with "type sudo".

Aliases are not a safety net

alias rm='rm -i' is not there in scripts, under sudo, or on the next machine. Do not let it teach you to type rm carelessly.

Protect your dot files

~/.bashrc and ~/.profile run at every login. They should be writable only by you.

Filed under

System information

Read alongside

historyLists the commands you have typed, numbered, so they can be searched and run again.whichPrints the full path of the program that a command name would run.