Enable and disable builtin shell commands. This allows
you to use a disk command which has the same name as a shell
builtin without specifying a full pathname. If -n is used, the
NAMEs become disabled; otherwise NAMEs are enabled. For example,
to use the `test' found in $PATH instead of the shell builtin
version, type `enable -n test'. On systems supporting dynamic
loading, the -f option may be used to load new builtins from the
shared object FILENAME. The -d option will delete a builtin
previously loaded with -f. If no non-option names are given, or
the -p option is supplied, a list of builtins is printed. The
-a option means to print every builtin with an indication of whether
or not it is enabled. The -s option restricts the output to the POSIX.2
`special' builtins. The -n option displays a list of all disabled builtins.