Hi,
I'm trying to confirm whether I'm doing something wrong or I'm running
into a limitation. I want to spawn arbitrary shell commands and send
input / capture output.
The typical uv_spawn example (code below) works fine for
non-backgrounded shell commands like these:
bash -c 'tee'
bash -c 'cat -'
but "backgrounded" shell commands do not capture input:
bash -c 'tee &'
bash -c 'cat - &'
For example, when the sample code below is modified with:
args[2] = "cat - &";
and invoked with:
$ echo foo | ./a.out
then "foo" is not printed.
Although intuitively it seems like this "should not" work, the reason
I bothered to ask is that the following *does* work:
args[2] = "echo foo &";
invoked with:
$ ./a.out
prints "foo". Here the "backgrounded" output was captured by libuv.
But in the cases above, input does not reach the backgrounded process.
Sample code follows:
================================================
#include <stdio.h>
#include <stdlib.h>
#include <inttypes.h>
#include <uv.h>
void exit_cb(uv_process_t *req, int64_t exit_status, int term_signal) {
fprintf(stderr, "Process exited with status %" PRId64 ",
signal %d\n", exit_status, term_signal);
uv_close((uv_handle_t*) req, NULL);
}
int main() {
uv_loop_t *loop = malloc(sizeof(uv_loop_t));
uv_loop_init(loop);
char* args[4];
args[0] = "/bin/bash";
args[1] = "-c";
args[2] = "cat - &";
args[3] = NULL;
uv_stdio_container_t child_stdio[3];
child_stdio[0].flags = UV_INHERIT_FD;
child_stdio[0].data.fd = 0;
child_stdio[1].flags = UV_INHERIT_FD;
child_stdio[1].data.fd = 1;
child_stdio[2].flags = UV_INHERIT_FD;
child_stdio[2].data.fd = 2;
uv_process_options_t options = {0};
options.exit_cb = exit_cb;
options.file = args[0];
options.args = args;
options.stdio_count = 3;
options.stdio = child_stdio;
int r;
uv_process_t child_req = {0};
if ((r = uv_spawn(loop, &child_req, &options))) {
fprintf(stderr, "%s\n", uv_strerror(r));
return 1;
} else {
fprintf(stderr, "Launched process with ID %d\n", child_req.pid);
}
return uv_run(loop, UV_RUN_DEFAULT);
}
================================================
Compiled with:
gcc -pthread -fno-omit-frame-pointer -Wall -g main.c
~/libuv/out/Debug/libuv.a -I ~/libuv/include/
Side note: in the actual application, rather than UV_INHERIT_FD I
would want to use (UV_CREATE_PIPE | UV_READABLE_PIPE) and
(UV_CREATE_PIPE | UV_WRITABLE_PIPE) so that application buffers can be
written to the spawned process.
Thanks for your time.
---
Justin M. Keyes
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