popen.c

unix环境高级编程的源代码

#include    <sys/wait.h>
#include    <errno.h>
#include    <fcntl.h>
#include    "ourhdr.h"

static pid_t    *childpid = NULL;
                        /* ptr to array allocated at run-time */
static int        maxfd;    /* from our open_max(), {Prog openmax} */

#define    SHELL    "/bin/sh"

FILE *
popen(const char *cmdstring, const char *type)
{
    int        i, pfd[2];
    pid_t    pid;
    FILE    *fp;

            /* only allow "r" or "w" */
    if ((type[0] != 'r' && type[0] != 'w') || type[1] != 0) {
        errno = EINVAL;        /* required by POSIX.2 */
        return(NULL);
    }

    if (childpid == NULL) {        /* first time through */
                /* allocate zeroed out array for child pids */
        maxfd = open_max();
        if ( (childpid = calloc(maxfd, sizeof(pid_t))) == NULL)
            return(NULL);
    }

    if (pipe(pfd) < 0)
        return(NULL);    /* errno set by pipe() */

    if ( (pid = fork()) < 0)
        return(NULL);    /* errno set by fork() */
    else if (pid == 0) {                            /* child */
        if (*type == 'r') {
            close(pfd[0]);
            if (pfd[1] != STDOUT_FILENO) {
                dup2(pfd[1], STDOUT_FILENO);
                close(pfd[1]);
            }
        } else {
            close(pfd[1]);
            if (pfd[0] != STDIN_FILENO) {
                dup2(pfd[0], STDIN_FILENO);
                close(pfd[0]);
            }
        }
            /* close all descriptors in childpid[] */
        for (i = 0; i < maxfd; i++)
            if (childpid[i] > 0)
                close(i);

        execl(SHELL, "sh", "-c", cmdstring, (char *) 0);
        _exit(127);
    }
                                /* parent */
    if (*type == 'r') {
        close(pfd[1]);
        if ( (fp = fdopen(pfd[0], type)) == NULL)
            return(NULL);
    } else {
        close(pfd[0]);
        if ( (fp = fdopen(pfd[1], type)) == NULL)
            return(NULL);
    }
    childpid[fileno(fp)] = pid;    /* remember child pid for this fd */
    return(fp);
}

int
pclose(FILE *fp)
{
    int        fd, stat;
    pid_t    pid;

    if (childpid == NULL)
        return(-1);        /* popen() has never been called */

    fd = fileno(fp);
    if ( (pid = childpid[fd]) == 0)
        return(-1);        /* fp wasn't opened by popen() */

    childpid[fd] = 0;
    if (fclose(fp) == EOF)
        return(-1);

    while (waitpid(pid, &stat, 0) < 0)
        if (errno != EINTR)
            return(-1);    /* error other than EINTR from waitpid() */

    return(stat);    /* return child's termination status */
}