cat命令的具体实现代码

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

#define BUFFERSIZE 4096

int main(int argc, char *argv[])
{
    int fd, fd_tty, n_chars;
    char buf[BUFFERSIZE];

    if (argc != 2)
    {   
        fprintf(stderr, "Usage: %s filename\n", *argv);
        exit(1);
    }   

    if ((fd = open(argv[1], O_RDONLY)) == -1) 
    {   
        perror("Open error!");
        exit(1);
    }   

    /* /dev/tty 表示输入终端 */
    if (fd_tty = open("/dev/tty", O_RDWR) == -1) 
    {   
        perror("Open error!");
        exit(1);
    }   

    while ((n_chars = read(fd, buf, BUFFERSIZE)) > 0)
    {   
        if (write(fd_tty, buf, n_chars) != n_chars)
        {   
            perror("Write error!");
            exit(1);
        }   
    }   
    
    if (close(fd) == -1) 
        perror("Error closing files!");
    
    return 0;
}