/*-
 * SPDX-License-Identifier: BSD-3-Clause
 *
 * Copyright (c) 1989, 1993
 *      The Regents of the University of California.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#include <sys/param.h>
#include <sys/stat.h>

#include <err.h>
#include <errno.h>
#include <fcntl.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

static void dofile(void);
static void usage(void) __dead2;

#define FILENAME        "nohup.out"
/*
 * POSIX mandates that we exit with:
 * 126 - If the utility was found, but failed to execute.
 * 127 - If any other error occurred. 
 */
#define EXIT_NOEXEC     126
#define EXIT_NOTFOUND   127
#define EXIT_MISC       127

int
main(int argc, char *argv[])
{
        int exit_status;

        while (getopt(argc, argv, "") != -1)
                usage();
        argc -= optind;
        argv += optind;
        if (argc < 1)
                usage();

        if (isatty(STDOUT_FILENO))
                dofile();
        if (isatty(STDERR_FILENO) && dup2(STDOUT_FILENO, STDERR_FILENO) == -1)
                /* may have just closed stderr */
                err(EXIT_MISC, "%s", argv[0]);

        (void)signal(SIGHUP, SIG_IGN);

        execvp(*argv, argv);
        exit_status = (errno == ENOENT) ? EXIT_NOTFOUND : EXIT_NOEXEC;
        err(exit_status, "%s", argv[0]);
}

static void
dofile(void)
{
        int fd;
        char path[MAXPATHLEN];
        const char *p;

        /*
         * POSIX mandates if the standard output is a terminal, the standard
         * output is appended to nohup.out in the working directory.  Failing
         * that, it will be appended to nohup.out in the directory obtained
         * from the HOME environment variable.  If file creation is required,
         * the mode_t is set to S_IRUSR | S_IWUSR.
         */
        p = FILENAME;
        fd = open(p, O_RDWR | O_CREAT | O_APPEND, S_IRUSR | S_IWUSR);
        if (fd != -1)
                goto dupit;
        if ((p = getenv("HOME")) != NULL && *p != '\0' &&
            (size_t)snprintf(path, sizeof(path), "%s/%s", p, FILENAME) <
            sizeof(path)) {
                fd = open(p = path, O_RDWR | O_CREAT | O_APPEND,
                    S_IRUSR | S_IWUSR);
                if (fd != -1)
                        goto dupit;
        }
        errx(EXIT_MISC, "can't open a nohup.out file");

dupit:
        if (dup2(fd, STDOUT_FILENO) == -1)
                err(EXIT_MISC, NULL);
        (void)fprintf(stderr, "appending output to %s\n", p);
}

static void
usage(void)
{
        (void)fprintf(stderr, "usage: nohup [--] utility [arguments]\n");
        exit(EXIT_MISC);
}