pipe2.c

unix环境高级编程的源代码

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

#define    DEF_PAGER    "/usr/bin/more"        /* default pager program */

int
main(int argc, char *argv[])
{
    int        n, fd[2];
    pid_t    pid;
    char    line[MAXLINE], *pager, *argv0;
    FILE    *fp;

    if (argc != 2)
        err_quit("usage: a.out <pathname>");
    if ( (fp = fopen(argv[1], "r")) == NULL)
        err_sys("can't open %s", argv[1]);

    if (pipe(fd) < 0)
        err_sys("pipe error");

    if ( (pid = fork()) < 0)
        err_sys("fork error");
    else if (pid > 0) {                                /* parent */
        close(fd[0]);        /* close read end */
            /* parent copies argv[1] to pipe */
        while (fgets(line, MAXLINE, fp) != NULL) {
            n = strlen(line);
            if (write(fd[1], line, n) != n)
                err_sys("write error to pipe");
        }
        if (ferror(fp))
            err_sys("fgets error");

        close(fd[1]);    /* close write end of pipe for reader */
        if (waitpid(pid, NULL, 0) < 0)
            err_sys("waitpid error");
        exit(0);

    } else {                                        /* child */
        close(fd[1]);    /* close write end */
        if (fd[0] != STDIN_FILENO) {
            if (dup2(fd[0], STDIN_FILENO) != STDIN_FILENO)
                err_sys("dup2 error to stdin");
            close(fd[0]);    /* don't need this after dup2 */
        }

            /* get arguments for execl() */
        if ( (pager = getenv("PAGER")) == NULL)
            pager = DEF_PAGER;
        if ( (argv0 = strrchr(pager, '/')) != NULL)
            argv0++;        /* step past rightmost slash */
        else
            argv0 = pager;    /* no slash in pager */

        if (execl(pager, argv0, (char *) 0) < 0)
            err_sys("execl error for %s", pager);
    }
}