Some commands must be implemented as shell builtins, so that they can mutate the shell state, a thing that would not be possible for an external program. A good example of such kind is the
cd command, which must change the shell's working directory.
Hush currently provides the following builtin commands:
cd: change the working directory to the given argument.
As Hush has no such thing as subshells, builtin commands may not be used in pipes, redirections, or capture blocks.