[系统运维]Linux中写C代码进行文件读写与权限修改等各类操作

C查看当前文件的权限

#include <unistd.h>
#include <stdio.h>
int main(int argc,char* argv[])
{
  char *my[3] = {0};
  my[0]="ls";
  my[1] = "-l";
  execv("/bin/ls",my);
  return 0;
}

C打开文件与关闭文件

参考：https://blog.csdn.net/annjeff/article/details/107086983?utm_medium=distribute.pc_relevant.none-task-blog-title-5&spm=1001.2101.3001.4242

#include <sys/types.h>                                                                                                                                         
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h> // fclose
#include <stdlib.h> //exit
#include <stdio.h>  //perror

int main()
{
    int fd; 
    // 光标在 open 身上，2 shift + k 即可跳至帮助文档
    
    // 打开文件,若该文件不存在则创建新文件
    fd = open("annNote", O_RDWR | O_CREAT, 0777);
    if(fd == -1){
        perror("create file");
        exit(1);
    }   
    // 关闭文件
    int ret = close(fd);
    if( ret == -1){
        perror("close file");
        exit(1);
    }   
    return 0;
}

Linux下用C语言使用write函数实现将键盘输入的内容写入文件

参考：https://blog.csdn.net/zxy131072/article/details/108238257

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

#define N 128

int main(int argc, const char *argv[])
{
    int  fd;
    char  buf[N] = { 0 };

    memset(buf, 0, sizeof(buf));
    
    if ((fd  = open(argv[1], O_WRONLY|O_CREAT|O_TRUNC, 0666)) < 0)
    {
           perror("open");  
		   return -1;
    }
    
    while (fgets(buf, 20, stdin) != NULL) 
    {
        if (strcmp(buf, "quit\n") == 0)
            break;
        write(fd, buf, strlen(buf));
    }
    
	close(fd);
	
	return 0;
}

Linux中C代码设置文件的权限

https://baike.baidu.com/item/MKDIR/9500968?fr=aladdin

实验需求

代码如下，创建代码为demo.c

#include<stdio.h> //标准输入输出函数
#include<stdlib.h> //C、C++语言的最常用的系统函数
#include<sys/types.h>
#include<sys/stat.h>
#include<syslog.h>
#include<string.h>
//补充缺失的头文件
#include<unistd.h>
#include <fcntl.h>
#include <unistd.h> // fclose
#include <stdlib.h> //exit
#include <stdio.h>  //perror

#define MAX 128
int chmd()
{
int c;
mode_t mode=S_IWUSR;
    printf("0: 0700\n1: 0400\n2: 0200\n3: 0100\n");
    printf("Please input your choice of change the mode of the file :");
    scanf("%d", &c);
    switch(c)
    {
        //参考：https://baike.baidu.com/item/MKDIR/9500968?fr=aladdin
        case 0:chmod("file1", S_IRWXU); break; //0700权限
// Mode flag: Read, write, execute by user.
//依据上面数字的提示定义其他case中文件权限的情况。
//补充代码：case1
   case 1: chmod("file1", S_IRUSR); break;//0400权限
//补充代码：case2
         case 2: chmod("file1", S_IWUSR); break;//0200权限
//补充代码：case3
        case 3: chmod("file1", S_IXUSR); break;//0100权限
        default:printf("You have a wrong choice! \n");
    }
    return 0;
}

int main()
{
    int fd;
    int num;
    int choice;
    char buffer[MAX];
    struct stat st;
    int n;
    char buf[1024];
    char* path="/bin/ls";
    char* argv[4]={"ls","-l","file1",NULL};
    while(1)
    {
        printf("*************************\n");
        printf("0. 退出\n");
        printf("1. 创建新文件\n");
        printf("2. 写文件\n");
        printf("3. 读文件\n");
        printf("4. 修改文件权限\n");
        printf("5. 查看当前文件的权限并退出\n");
        printf("*************************\n");
        printf("Please input your choice(0-6):");
        scanf("%d", &choice);
        
        switch(choice)
        {
            case 0: close(fd);
            exit(0);
            case 1:
                fd=open("file1",O_RDWR|O_TRUNC|O_CREAT,0750);
/* 
O_RDWR : file open mode: Read/Write
O_TRUNC : file open mode: Truncate file to length 0
O_CREAT : file open mode: Create if file does not yet exist.
0750: file access permission bits -rwxr-x---当前用户rwx；同组用户r-x；其他用户无权限
*/

                if(fd==-1)
                    printf("File Create Failed!\n");
                else
                    printf("fd=%d\n",fd);
                break;
            case 2:
                //补充代码：用read与write函数，从键盘里面读取信息，写到filel里面
                printf("输入需要写入到file1中的内容\n");
                fgets(buf, 20, stdin);//读掉上一行的行末符号
                fgets(buf, 20, stdin);
                fd = open("file1", O_RDWR | O_CREAT, 0777);
                write(fd, buf, strlen(buf));
                printf("写入成功\n");
                break;
            case 3:
                fd = open("file1", O_RDWR | O_CREAT, 0777);
                printf("读取file1成功\n");
                while((n = read(fd, buf, 1024)) > 0 ){
                    printf("%s\n",buf);
                }
                break;
                //补充代码：用read与write函数，把file1文件的内容在屏幕上输出
            case 4:
                chmd();
                printf("Change mode success!\n");
                break;
            case 5:
                printf("输出file1文件的权限、拥有者、拥有组、文件名、大小等\n");
                execv(path, argv); //-ls -l 显示文件完整的信息，包括权限，拥有者，拥有组，文件名，大小等
                break;
            default:
                printf("You have a wrong choice!\n");
        }
    }
    return 0;
}