Linux/UNIX编程：实现简单 tee 命令

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/stat.h>
#include <errno.h>

#ifndef BUF_SIZE
#define BUF_SIZE 1024
#endif

int main(int argc,char const *argv[])
{
    int outputFd;
    /* 命令格式要求为 `tee [-a] file`，没有判断参数是否合法*/
    if(argc == 3){ //加了 -a 选项，则以追加的方式写数据
        outputFd = open(argv[2],O_WRONLY | O_CREAT | O_APPEND,S_IRUSR | S_IWUSR | S_IRGRP); //rw-r-----
    } else if (argc == 2){
        outputFd = open(argv[1],O_WRONLY | O_CREAT,S_IRUSR | S_IWUSR | S_IRGRP); //rw-r-----
    }

    if(outputFd == -1){
        perror(strerror(errno));
        exit(EXIT_FAILURE);
    }

    char buffer[BUF_SIZE];
    int readNum;

    while((readNum = read(STDIN_FILENO,buffer,BUF_SIZE)) > 0){
        ssize_t fileWrNum = write(outputFd,readNum); //向指定文件写出数据
        ssize_t stdoutWrNum = write(STDOUT_FILENO,readNum); //向标准输出写入数据

        if(fileWrNum != readNum || stdoutWrNum != readNum){ //判断是否写成功
            perror("couldn't write the whole buffern");
            exit(EXIT_FAILURE);
        }
    }
    if(readNum == -1){ //判断是否读取成功
        perror(strerror(errno));
        exit(EXIT_FAILURE);
    }

    if(close(outputFd) == -1){ //判断是否成功关闭
        perror(strerror(errno));
        exit(EXIT_FAILURE);
    }

　　 exit(EXIT_SUCCESS);

}