HELP SHELL_LIB                Run commands with output, status and control

    uses shell;

What sysobey never gave you: captured output, exit status, separate
stderr, background jobs, kills and timeouts.  Commands run via
'/bin/sh -c'.  Status is the decoded exit code (0-255); a command
killed by a signal reports 128 + signum (so SIGTERM = 143), the
shell convention.  (HELP * SHELL is the classic 1983 guide to using
a Unix shell from Ved — different thing entirely.)

shell_run(CMD) -> (OUTPUT, STATUS)
    Stdout and stderr captured together (2>&1 semantics).

        shell_run('git rev-parse HEAD') -> (out, status);

shell_run_full(CMD) -> (OUTPUT, ERROUT, STATUS)
    Stderr captured separately (via a temp file, so large stderr
    cannot deadlock the pipe).

shell_lines(CMD) -> (LINES, STATUS)
    Output as a list of line strings.

shell_bg(CMD) -> JOB
shell_wait(JOB) -> (OUTPUT, STATUS)
shell_kill(JOB)
    Start a command in the background, later collect it (blocking),
    or SIGTERM it first.  Always shell_wait a job you started, or a
    zombie process remains.

shell_timeout(CMD, SECS) -> (OUTPUT, STATUS)
    Run with a watchdog: the command is SIGTERMed after SECS seconds
    (status 143).  Fast commands return immediately — the watchdog is
    detached from the output pipe.  The shell may append its own
    'Terminated' notice to merged output when the timeout fires.

See also: LIB * PIPEIN (character repeaters from commands), sysobey,
sys_fork/sys_wait (the primitives), tools/tests/test_shell.p.

--- pop/help/shell_lib