Signal Termination

The traps of the preceding sections (overflow, division by zero, out-of-bounds indexing) end a program from inside with the panic exit code 101. A program may also be ended from outside the language's control flow when the host operating system delivers a signal whose default disposition is to terminate the process. Rue installs no signal handlers, so such signals keep their platform-default behavior. This section describes the observable exit status in that case; because the trigger is external to the language, these paragraphs are informative rather than normative.

On a Unix host, a process terminated by signal number signum reports the exit status 128 + signum under the conventional shell encoding (for example, the $? value observed by a parent shell). This follows the platform convention and is not defined by Rue itself; the exact encoding is that of the host operating system and its shell.

A Rue program whose standard output (or any output stream it writes to) is a pipe or socket whose reading end has been closed is terminated by SIGPIPE on its next write to that stream, exiting with status 141 (that is, 128 + SIGPIPE, where SIGPIPE is 13 on Linux and macOS). This is Rue's defined default: it matches the standard Unix behavior for programs in a pipeline (such as rue_program | head), so a downstream reader that stops consuming input promptly and cleanly ends the producer. The runtime's write path does not intercept this case — the signal is delivered before the failing write syscall returns, so the write's error result is never observed (see the write_stderr/write_stdout documentation in rue-runtime).

A write that fails without a signal — for example, writing to a file descriptor that has been closed outright (EBADF) rather than to a broken pipe — does not terminate the program. The runtime discards the error and execution continues, because there is no meaningful recovery and the process is typically about to exit regardless.

Making the SIGPIPE response configurable (an analogue of Rust's -Zon-broken-pipe, e.g. resetting the disposition so writes observe EPIPE instead of dying) is a separate, future feature and is intentionally out of scope here; the default described above is the only behavior Rue currently provides.