The alias substitution mechanism provides a simple way for the user to change the meaning of a command, or to build a new command from existing commands. The mechanism substitutes a predefined word list in place of the first word on a command line (or the first word on a line in a script).
The built-in command 'unalias' is used to undefine aliases which have been defined with the command 'alias'
Unalias expects its arguments to be kewords referring to currently defined aliases. Any such aliases will be cleared from MacShell, and no longer used by its alias substitution mechanism.