Operating system functions.
System.os.posix: Common POSIX functions and constants.args: Arguments passed in from the shell.dylib_extension: The dynamic library extension on this system.chdir(newcwd, ): Changes the current working directory.chmod(name, permission, ): Changes permissions for a file or directory.envGet(var, ): Retrieve contents of environment variable.envSet(var, val, ): Set contents of environment variable to given value.fork(): Forks off a new process.getcwd(): Gets the current working directory.mkdir(name, ): Creates a new directory.rmdir(name, ): Removes a directory.system(cmd, ): Executes system command.