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On 02/27/2010 08:34 PM, Luiz Henrique de Figueiredo wrote:
It appears that the command line Lua interpreter does not trap SIGPIPE:
It does not. lua.c is mostly an ANSI C program. It'd have to be a POSIX
program to trap SIGPIPE.
Then how pcall() be implemented ?
rjek@trite:~$ lua
Lua 5.1.4  Copyright (C) 1994-2008, PUC-Rio
f = assert(io.popen("true", "w"))
f:write "Hello, world."
rjek@trite:~$ echo $?
I get this in Linux:
f = assert(io.popen("true", "w"))
=f:write "Hello, world."
Broken pipe
(program exits
I'm not sure how the situation could be improved much.
I don't think it can be improved at all if f:write returns true. Of course,
f:write probably just buffers the output because if I replace f:close with
f:flush I get the same error (Broken pipe).

Exactly same broken pipe can be verified using C:

#include <stdio.h>
#include <unistd.h>

int main(int argc, char const* argv[])
    FILE * f = popen("true", "w");
    usleep(1 << 18); // sleep sometime, pipe should be invalid.
    fprintf(f, "hello world");
    pclose(f); // cause exit, code 141
    return 0;

Since POPEN manual page says "output popen() streams are fully buffered by default."
I think f:write return true is resonable.

I am wondering why pcall(function() f:write('bla') f:flush() end) is not safe? Because it didn't trap SIGPIPE? Is it the same question?