utils-std

nohup.c (2735B)

// utils-std: Collection of commonly available Unix tools
// SPDX-FileCopyrightText: 2017 Haelwenn (lanodan) Monnier <contact+utils@hacktivis.me>
// SPDX-License-Identifier: MPL-2.0
#define _POSIX_C_SOURCE 200809L
#include <assert.h>
#include <errno.h>
#include <fcntl.h>  // open
#include <limits.h> // PATH_MAX
#include <signal.h>
#include <stdbool.h>
#include <stdio.h>    // fprintf
#include <stdlib.h>   // getenv
#include <string.h>   // strerror
#include <sys/stat.h> // S_IRUSR, S_IWUSR
#include <unistd.h>   // isatty
const char *argv0 = "nohup";
static void
usage(void)
{
	fprintf(stderr, "Usage: nohup command [args ...]\n");
}
int
main(int argc, char *argv[])
{
	int nohup_fd = -1;
	if(argc <= 1)
	{
		usage();
		return 127;
	}
	if(signal(SIGHUP, SIG_IGN) == SIG_ERR)
	{
		fprintf(stderr, "%s: error: Failed to set SIGHUP as ignored: %s\n", argv0, strerror(errno));
		return 127;
	}
	assert(errno == 0);
	if(isatty(1))
	{
		assert(errno == 0);
		nohup_fd = open("nohup.out", O_WRONLY | O_APPEND | O_CREAT, S_IRUSR | S_IWUSR);
		if(nohup_fd < 0)
		{
			fprintf(stderr,
			        "%s: warning: Failed opening ./nohup.out (%s), fallbacking to ~/nohup.out\n",
			        argv0,
			        strerror(errno));
			char *home = getenv("HOME");
			if(!home)
			{
				fprintf(stderr,
				        "%s: error: $HOME is undefined, can't fallback writing from ./nohup.out to "
				        "~/nohup.out\n",
				        argv0);
				return 127;
			}
			char home_nohup[PATH_MAX];
			if(snprintf(home_nohup, sizeof(home_nohup), "%s/nohup.out", home) < 0)
			{
				fprintf(stderr,
				        "%s: error: Failed concatenating $HOME and '/nohup.out': %s\n",
				        argv0,
				        strerror(errno));
				return 127;
			}
			nohup_fd = open(home_nohup, O_WRONLY | O_APPEND | O_CREAT, S_IRUSR | S_IWUSR);
			if(nohup_fd < 0)
			{
				fprintf(stderr, "%s: error: Failed opening ~/nohup.out: %s\n", argv0, strerror(errno));
				return 127;
			}
		}
		if(dup2(nohup_fd, 1) < 0)
		{
			fprintf(stderr,
			        "%s: error: Failed assigning 'nohup.out' to stdout: %s\n",
			        argv0,
			        strerror(errno));
			return 127;
		}
		if(isatty(2))
		{
			assert(errno == 0);
			if(dup2(1, 2))
			{
				fprintf(
				    stderr, "%s: error: Failed assigning stdout to stderr: %s\n", argv0, strerror(errno));
				return 127;
			}
		}
		else
			errno = 0; // isatty sets errno on returning false
	}
	else
		errno = 0; // isatty sets errno on returning false
	argc -= 1;
	argv += 1;
	(void)argc;
	assert(argv[0]);
	assert(errno == 0);
	if(execvp(argv[0], argv) < 0)
	{
		fprintf(stderr, "%s: error: Failed executing '%s': %s\n", argv0, argv[0], strerror(errno));
		return (errno == ENOENT) ? 127 : 126;
	}
	assert(false);
}