How catch ctrl-c in lua when ctrl-c is sent via the command line

Question

I would like to know when the user from a command line presses control-c so I can save some stuff.

How do I do this? I've looked but haven't really seen anything.

Note: I'm somewhat familiar with lua, but I'm no expert. I mostly use lua to use the library Torch (http://torch.ch/)

Unfortunately, on LuaJIT Ctrl-C is not catchable with pcall. — Egor Skriptunoff, Sep 01 '15 at 21:03
How exactly do you catch it with pcall? pcall(io.read()) won't catch double ctrl-c, only ctrl-c+enter. — Karl P, Sep 04 '15 at 16:38
@KarlP - `lua -e"print(pcall(io.read))"` is interrupted by `Ctrl-C` without pressing `Enter`. Describe your testing method. — Egor Skriptunoff, Oct 06 '15 at 16:39
@EgorSkriptunoff depends on the underlying libc I guess. OpenWrt/uclibc you need the enter, desktop linux you don't. — Karl P, Nov 03 '15 at 14:19

score 6 · Answer 1 · answered Dec 22 '15 at 05:52

Implementing a SIGINT handler is straightforward using the excellent luaposix library:

local signal = require("posix.signal")

signal.signal(signal.SIGINT, function(signum)
  io.write("\n")
  -- put code to save some stuff here
  os.exit(128 + signum)
end)

Refer to the posix.signal module's API documentation for more information.

score 2 · Answer 2 · answered Sep 05 '15 at 04:50

windows : SetConsoleCtrlHandler

linux : signal

There are two behaviors of the signal which are undesirable, which will cause complexities in the code.

Program termination
Broken IO

The first behavior can be caught and remembered in a C program by using SetConsoleCtrlHandler/signal. This will allow your function to be called, and you can remember that the system needs to shutdown. Then at some point in the lua code you see it has happened (call to check), and perform your tidy up and shutdown.

The second behavior, is that a blocking operation (read/write) will be cancelled by the signal, and the operation will be unfinished. That would need to be checked at each IO event, and then re-started, or cancelled as appropriate.

Blocking operations are EINTR'ed on any signal, not just SIGINT (that is sent to process by terminal on C-c). But this only happens if SA_RESTART was not set when installing a new signal handler. — user3125367, Sep 14 '15 at 13:07

score 2 · Answer 3 · answered Sep 09 '15 at 05:54

There exists io libraries that support this. I know zmq and libuv

Libuv example with lluv binding - https://github.com/moteus/lua-lluv/blob/master/examples/sig.lua

ZeroMQ return EINTR from poll function when user press Ctrl-C

But I do not handle thi byself

score -1 · Answer 4 · edited Sep 16 '15 at 05:43

-1

require('sys')
sys.catch_ctrl_c()

I use this to catch the exit from cli.

edited Sep 16 '15 at 05:43

Unheilig

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answered Sep 16 '15 at 02:51

Jin Zhou

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I'm getting `stdin:1: module 'sys' not found: ...` if I try this at either the Lua or LuaJIT CLI. – i336_ Nov 25 '19 at 10:31

How catch ctrl-c in lua when ctrl-c is sent via the command line

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