8. Process Control and Jobs

Lash exposes Bash process control with structured syntax for the common cases.

shift

shift
shift 2

shift defaults to 1. Lash guards the generated Bash so shifting past the end clears the argument list instead of failing halfway through.

subshell

subshell
    cd build
    make
end

subshell ... end lowers to a Bash subshell block:

(
  ...
)

Capturing subshell status or pid

var status = 0
subshell into status
    false
end

var pid = 0
subshell into pid
    sleep 1
end &

For a foreground subshell, into captures $?. For a background subshell, into captures $!.

coproc

var copid = 0

coproc into copid
    sh "cat"
end

coproc ... end lowers to Bash coproc { ... }. into captures ${COPROC_PID}.

wait

wait
wait pid
wait pid into status

wait lowers to Bash wait. into captures the resulting exit status.

wait jobs

subshell
    sleep 1
end &

coproc
    sleep 1
end

wait jobs

wait jobs waits for jobs that Lash tracks from background subshell and coproc statements in the current analysis scope. It does not discover arbitrary jobs started by raw shell commands.

The compiler warns when wait jobs has no tracked jobs.

trap and untrap

fn cleanup()
    echo "cleanup"
end

trap EXIT into cleanup()
trap INT "echo interrupted"
untrap INT

trap SIGNAL into function() registers a Lash function as the handler. Handler calls cannot include arguments. trap SIGNAL "command" emits a Bash command handler. untrap SIGNAL clears the trap.

Valid trap signals are checked by the compiler.