builtin prints nothing and returns exit code 0. This is in accordance with
help builtin, which shows all parameters as optional. But why isn't this no-op an error? Is there a use case for this? A more useful result would be an error code or, even better, listing the currently available builtins.
Bash built-ins are inconsistent and poorly documented.
Here's an example:
$ help command command: command [-pVv] command [arg ...] Runs COMMAND with ARGS ignoring shell functions. If you have a shell function called 'ls', and you wish to call the command `ls', you can say "command ls". If the -p option is given, a default value is used for PATH that is guaranteed to find all of the standard utilities. If the -V or -v option is given, a string is printed describing COMMAND. The -V option produces a more verbose description. $ command; echo $? 0
command the return code
$? -eq 0 and there is no error on
$ help disown disown: disown [-h] [-ar] [jobspec ...] By default, removes each JOBSPEC argument from the table of active jobs. If the -h option is given, the job is not removed from the table, but is marked so that SIGHUP is not sent to the job if the shell receives a SIGHUP. The -a option, when JOBSPEC is not supplied, means to remove all jobs from the job table; the -r option means to remove only running jobs. $ disown; echo $? -bash: disown: current: no such job 1
All the arguments are optional but it returns
$? -eq 1 when there are none.
I've even compiled the newest Bash 4.2 and here are my results:
$ help command command: command [-pVv] command [arg ...] Execute a simple command or display information about commands. Runs COMMAND with ARGS suppressing shell function lookup, or display information about the specified COMMANDs. Can be used to invoke commands on disk when a function with the same name exists. Options: -p use a default value for PATH that is guaranteed to find all of the standard utilities -v print a description of COMMAND similar to the `type' builtin -V print a more verbose description of each COMMAND Exit Status: Returns exit status of COMMAND, or failure if COMMAND is not found. $ command; echo $? 0
There's a new section "Exit Status" and
command is still an optional argument. Even worse than 3.x. The same for other built-ins.
So, you're right. Bash built-ins are a mess and should be fixed.