unset: unset [-f] [-v] [name ...]
Unset values and attributes of shell variables and functions.
For each NAME, remove the corresponding variable or function.
Without options, unset first tries to unset a variable, and if that fails, tries to unset a function.
Some variables cannot be unset; also see `readonly'.
Exit Status:
Returns success unless an invalid option is given or a NAME is read-only.