forkdup.c

Linux 0.01内核 T-Shell 比较完整的shell功能

/* forkdup.c */
/* This program executes /bin/cat with stdin coming from f1, and stdout
going to f2.  This is all done with fork, exec, and dup: */

#include <stdio.h>
#include <fcntl.h>

main(int argc, char **argv, char **envp)
{
    int fd1, fd2;
    int dummy;
    char *newargv[2];

    if (fork() == 0) {
        fd1 = open("f1", O_RDONLY);
        if (fd1 < 0) {
            perror("catf1f2: f1");
            exit(1);
        }

        if (dup2(fd1, 0) != 0) {
            perror("catf1f2: dup2(f1, 0)");
            exit(1);
        }
        close(fd1);

        fd2 = open("f2", O_WRONLY | O_TRUNC | O_CREAT, 0644);
        if (fd2 < 0) {
            perror("catf1f2: f2");
            exit(2);
        }

        if (dup2(fd2, 1) != 1) {
            perror("catf1f2: dup2(f2, 1)");
            exit(1);
        }
        close(fd2);

        newargv[0] = "cat";
        newargv[1] = (char *) 0;

        execve("/bin/cat", newargv, envp);
        perror("execve(bin/cat, newargv, envp)");
        exit(1);
    } else {
        wait(&dummy);
    }
}