Implementation of Linux cp command

CP commands

This article will show the code to implement the Linux cp command

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Article Directory

• Series of articles catalog
• Preface
• 1. The idea of ​​realizing the CP command
• Second, the steps
  • 1. Introduce the library
  • 2. Code to implement CP commands
• to sum up

 

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Preface

Have you ever wondered how the command in Linux implements the function of the command? Here I will introduce the code.

 

1. The idea of ​​realizing the CP command

To copy the content of a file to an existing file, or copy to a newly created file, the first step : open the file to be copied; the second step : copy the file to the buffer area; the third step : Open and create a new file; Step 4 : Write the contents of the buffer area to the newly created file; Step 5 : Close the file

Second, the steps

1. Introduce the library

code show as below:

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

 

2. Code to implement CP commands

code show as below:

int main(int argc,char **argv)
{
        int fdSrc;
        int fdDes;
        char *readBuf = NULL;

    //判断使用该命令的方式是否正确 
        if(argc != 3){
                printf("param error\n");
                exit(-1);
        }

    //第一步：打开待复制的文件
        fdSrc = open(argv[1],O_RDWR);
        int size = lseek(fdSrc,0,SEEK_END);
        lseek(fdSrc,0,SEEK_SET);    //将光标移动待文件开头
    
    //第二步：将待复制的文件读取到缓存区 readBuf
        readBuf = (char *)malloc(sizeof(char)*size+8);
        int n_read = read(fdSrc,readBuf,size);

    //第三步：打开或者新创建一个文件
        fdDes = open(argv[2],O_RDWR|O_CREAT|O_TRUNC,0600);
    
    //第四步：将缓存区里的内容写入到新打开或者创建的文件中
        int n_write = write(fdDes,readBuf,size);

    //第五步：关闭文件，以达到保护文件的作用
        close(fdSrc);
        close(fdDes);
        return 0;
}

 

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to sum up

After knowing how the commands are implemented, are you curious about functions such as open(), read(), write(), etc. How do these functions implement these functions?