linux系统下编写myecho，mycat和mycp的两种实现

 myecho.c

• myecho.c的功能与系统echo程序相同
• 接受命令行参数，并将参数打印出来，例子如下：

  $ ./myecho x
  x
  $ ./myecho a b c
  a b c

#include <stdio.h>

int main(int argc, char *argv[])
{
    if(argc < 2){
        printf("lack of argurments");
        return -1;
    }
    printf("%s\n", argv[1]);

    return 0;
}

第二种方法：使用execl（或execv）函数调用echo命令

#include <unistd.h>
#include <stdio.h>
#include <sys/types.h>
#include <sys/wait.h>

int main(int argc, char *argv[]){
    if(argc < 2){
        printf("lack of argurments");
        return -1;
    }
    pid_t pid;
    pid = fork();
    if(pid == 0){
        execl("/bin/echo", "echo", argv[1], NULL);
    }
    wait(NULL);

    return 0;
}

 mycat.c

• mycat.c的功能与系统cat程序相同
• mycat将指定的文件内容输出到屏幕，例子如下：
• 要求使用系统调用open/read/write/close实现

  $ cat /etc/passwd 
  root:x:0:0:root:/root:/bin/bash
  daemon:x:1:1:daemon:/usr/sbin:/usr/sbin/nologin
  bin:x:2:2:bin:/bin:/usr/sbin/nologin
  ...
  $ ./mycat /etc/passwd 
  root:x:0:0:root:/root:/bin/bash
  daemon:x:1:1:daemon:/usr/sbin:/usr/sbin/nologin
  bin:x:2:2:bin:/bin:/usr/sbin/nologin
  ...

#include <stdio.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <string.h>
#include <unistd.h>
#define MAXSIZE 65535

int main(int argc, char *argv[])
{
    if(argc < 2){
        printf("lack of argurments");
        return -1;
    }
    int fd;
    fd = open(argv[1], O_RDONLY);
    if(fd < 0){
        printf("open file failure\n");
        return -1;
    }
    char str[MAXSIZE];
    int count = read(fd, str, MAXSIZE - 1);
    while(count > 0){
        printf("%s\n", str);
        memset(str, '\0', MAXSIZE);
        count = read(fd, str, MAXSIZE - 1);
    }
    close(fd);
    return 0;
}

 第二种方法

#include <unistd.h>
#include <stdio.h>
#include <sys/types.h>
#include <sys/wait.h>

int main(int argc, char *argv[]){
    if(argc < 2){
        printf("lack of argurments");
        return -1;
    }
    pid_t pid;
    pid = fork();
    if(pid == 0){
        execl("/bin/cat", "cat", argv[1], NULL);
    }
    wait(NULL);

    return 0;
}

mycp.c

• mycp.c的功能与系统cp程序相同
• 将源文件复制到目标文件，例子如下：
• 要求使用系统调用open/read/write/close实现

  $ cat /etc/passwd
  root:x:0:0:root:/root:/bin/bash
  daemon:x:1:1:daemon:/usr/sbin:/usr/sbin/nologin
  bin:x:2:2:bin:/bin:/usr/sbin/nologin
  ...
  $ ./mycp /etc/passwd passwd.bak 
  $ cat passwd.bak
  root:x:0:0:root:/root:/bin/bash
  daemon:x:1:1:daemon:/usr/sbin:/usr/sbin/nologin
  bin:x:2:2:bin:/bin:/usr/sbin/nologin
  ...

#include <stdio.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <string.h>
#include <unistd.h>
#define MAXSIZE 65535

int main(int argc, char *argv[])
{
    if(argc < 3){
        printf("lack of argurments");
        return -1;
    }
    int inFd, outFd;
    inFd = open(argv[1], O_RDONLY);
    outFd = open(argv[2], O_WRONLY | O_TRUNC | O_CREAT);
    if(inFd < 0){
        printf("open inFile failure\n");
        return -1;
    }
    if(outFd < 0){
        printf("open outFile failure\n");
        return -1;
    }
    char str[MAXSIZE];
    int count = read(inFd, str, MAXSIZE - 1);
    while(count > 0){
        write(outFd, str, strlen(str));
        memset(str, '\0', MAXSIZE);
        count = read(inFd, str, MAXSIZE - 1);
    }
    close(inFd);close(outFd);
    return 0;
}

 第二种方法

#include <unistd.h>
#include <stdio.h>
#include <sys/types.h>
#include <sys/wait.h>

int main(int argc, char *argv[]){
    if(argc < 3){
        printf("lack of argurments");
        return -1;
    }
    pid_t pid;
    pid = fork();
    if(pid == 0){
        execl("/bin/cp", "cp", argv[1], argv[2], NULL);
    }
    wait(NULL);

    return 0;
}