system.c

UNIX编程高级环境（第二版）的信号部分的程序源码

#include    <sys/types.h>
#include    <sys/wait.h>
#include    <errno.h>
#include    <signal.h>
#include    <unistd.h>

int
system(const char *cmdstring)    /* with appropriate signal handling */
{
    pid_t                pid;
    int                    status;
    struct sigaction    ignore, saveintr, savequit;
    sigset_t            chldmask, savemask;

    if (cmdstring == NULL)
        return(1);        /* always a command processor with Unix */

    ignore.sa_handler = SIG_IGN;    /* ignore SIGINT and SIGQUIT */
    sigemptyset(&ignore.sa_mask);
    ignore.sa_flags = 0;
    if (sigaction(SIGINT, &ignore, &saveintr) < 0)
        return(-1);
    if (sigaction(SIGQUIT, &ignore, &savequit) < 0)
        return(-1);

    sigemptyset(&chldmask);            /* now block SIGCHLD */
    sigaddset(&chldmask, SIGCHLD);
    if (sigprocmask(SIG_BLOCK, &chldmask, &savemask) < 0)
        return(-1);

    if ( (pid = fork()) < 0) {
        status = -1;    /* probably out of processes */

    } else if (pid == 0) {            /* child */
            /* restore previous signal actions & reset signal mask */
        sigaction(SIGINT, &saveintr, NULL);
        sigaction(SIGQUIT, &savequit, NULL);
        sigprocmask(SIG_SETMASK, &savemask, NULL);

        execl("/bin/sh", "sh", "-c", cmdstring, (char *) 0);
        _exit(127);        /* exec error */
    } else {                        /* parent */
        while (waitpid(pid, &status, 0) < 0)
            if (errno != EINTR) {
                status = -1; /* error other than EINTR from waitpid() */
                break;
            }
    }

        /* restore previous signal actions & reset signal mask */
    if (sigaction(SIGINT, &saveintr, NULL) < 0)
        return(-1);
    if (sigaction(SIGQUIT, &savequit, NULL) < 0)
        return(-1);
    if (sigprocmask(SIG_SETMASK, &savemask, NULL) < 0)
        return(-1);

    return(status);
}