6-5-tee.c

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


int main(int argc, const char *argv[])
{
    if (argc != 2) 
    {
        fprintf(stderr, "usage: %s <file>\n", basename(argv[0]));
        return 1;
    }
    int filefd = open(argv[1], O_CREAT | O_WRONLY | O_TRUNC, 0666);
    assert(filefd > 0);

    int pipefd_stdout[2];
    int ret = pipe(pipefd_stdout);
    assert(ret != -1);
    
    int pipefd_file[2];
    ret = pipe(pipefd_file);
    assert(ret != -1);

    /*将标准输入内容输入管道 pipefd_stdout */
    ret = splice(STDIN_FILENO, NULL, pipefd_stdout[1], NULL,
                32678, SPLICE_F_MORE | SPLICE_F_MOVE);
    assert(ret != -1);
    
    /*将管道pipefd_stdout的输出复制到管道pipefd_file的输入端 */
    ret = tee(pipefd_stdout[0], pipefd_file[1], 32678, SPLICE_F_NONBLOCK);
    assert(ret != -1);
    /*将pipefd_file的输出定向到文件描述符file_fd上，从而将标准输入的内容写入文件
     * */
    ret = splice(pipefd_file[0], NULL, filefd, NULL,
                32678, SPLICE_F_MORE | SPLICE_F_MOVE);
    assert(ret != -1);

    /*将管道pipefd_stdout的输出定向到标准输出， 其内容和写入文件的内容完全一致
     * */
    ret = splice(pipefd_stdout[0], NULL, STDOUT_FILENO, NULL,
                32678, SPLICE_F_MORE | SPLICE_F_MOVE);
    assert(ret != -1);

    close(filefd);
    close(pipefd_stdout[0]);
    close(pipefd_stdout[1]);
    close(pipefd_file[0]);
    close(pipefd_file[1]);
    return 0;
}