This mimics GNU Bash built-ins and Coreutils more closely. It allows the user to tell usage and other errors apart by their exit status.

From the Bash Reference Manual:

All of the Bash builtins return an exit status of zero if they succeed and a non-zero status on failure, so they may be used by the conditional and list constructs. All builtins return an exit status of 2 to indicate incorrect usage, generally invalid options or missing arguments.

From the GNU ls(1) manual:

   Exit status:
       0      if OK,
       1      if minor problems (e.g., cannot access subdirectory),
       2      if serious trouble (e.g., cannot access command-line
              argument).