Aliases are commands that expand to a longer input line. For example,
ll is a common alias for ls -l, and would be defined
with the command invocation ‘alias ll ls -l’; with this defined,
running ‘ll foo’ in Eshell will actually run ‘ls -l foo’.
Aliases defined (or deleted) by the alias command are
automatically written to the file named by eshell-aliases-file,
which you can also edit directly (although you will have to manually
reload it).