Lua: os.execute("sleep n") in infinite loop can't be stopped by ^C

Question

In lua 5.2.4, when using the widely used os.execute('sleep n') method in an infinite loop, the program can't be stopped by ^C (Ctrl-C).

Minimal example:

while true do
    print("HELLO!")
    os.execute("sleep 3")
end

My questions are:

1. Is this expected behavior? I would have guessed the program receives the ^C signal after returning from the os.execute command.

2. Is there a "builtin" way to sleep efficiently?

Answer 1

Control-c is most probably being caught by the shell spawned by os.execute, not by Lua. You need to look at the code returned by os.execute. When the command ends normally, os.execute returns true,"exit",rc. Otherwise, it returns nil,etc. When it is interrupted with control-c, it returns nil,"signal",2 in my machine.

Bottom line, try this code:

while true do
    print("HELLO!")
    if not os.execute("sleep 3") then break end
end