Aliases are quick and simple ways to make one command stand for a whole command line, expressed as a string. They are perhaps the best-known way to customize behavior in the Bash shell, but they are also the least flexible.
Depending on your system, it's possible you already have an alias or two defined by your startup scripts. When the builtin alias command is entered with no arguments, it lists all of the aliases defined in the current Bash session.
For example, on a Debian GNU/Linux server, a new user might have the following alias defined:
bash$ alias alias ls='ls --color=auto'
This is also evident from running the type command on ls with the -a switch, which informs us that the command used is an alias:
bash$ type -a ls ls is ...
