Unset values and attributes of shell variables and functions.
For each NAME, remove the corresponding variable or function.
Options:
-f
[tab]treat each NAME as a shell function
-v
[tab]treat each NAME as a shell variable
-n
[tab]treat each NAME as a name reference and unset the variable itself
[tab][tab]rather than the variable it references
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.
