cp命令的实现代码

#include <unistd.h>
#include <stdio.h>
#include <fcntl.h>int main(int argc, char* argv[]) {if (argc != 3) {fprintf(stderr, "Usage: %s <source_file> <destination_file>\n", argv[0]);return 1;}int fd = open(argv[1], O_RDONLY); // 打开源文件，只读方式if (fd < 0) {perror("打开源文件错误");return 1;}char buf[256];int rd = read(fd, buf, sizeof(buf)); // 读取源文件内容if (rd < 0) {perror("读取源文件失败");close(fd);return 1;}close(fd);int fd1 = open(argv[2], O_WRONLY | O_CREAT | O_TRUNC, 0664); // 创建或打开目标文件，截断内容if (fd1 < 0) {perror("打开目标文件错误");return 1;}int wd = write(fd1, buf, rd); // 将从源文件读取的内容写入目标文件if (wd < 0) {perror("写入目标文件错误");close(fd1);return 1;}close(fd1);return 0;
}

pwd指令

#include<unistd.h>
#include<fcntl.h>
#include<stdio.h>
#include<stdlib.h>int main(int argc,char*argv[])
{char buf[256];getcwd(buf,256);printf("\n%s\n",buf);return 0;}

ls指令

#include <stdio.h>
#include <stdlib.h>
#include <dirent.h>int main(int argc,char*argv[]) {// DIR *dir;// struct dirent *ent;// dir = opendir(".");// if (dir == NULL) {//     perror("Unable to open directory");//     return EXIT_FAILURE;// }// while ((ent = readdir(dir)) != NULL) {//     printf("%s\n", ent->d_name);// }// closedir(dir);DIR *dp;struct dirent *sdp;dp = opendir(argv[1]);if(dp==NULL){perror("opendir error");exit(1);}int count = 0;while((sdp= readdir(dp))!=NULL){printf("%-20s\t",sdp->d_name);count++;if(count%5!=0){continue;}else{printf("\n");}}printf("\n");closedir(dp);return EXIT_SUCCESS;
}

cat指令

#include<stdio.h>
#include<stdlib.h>
#include<unistd.h>
#include<fcntl.h>
#include<string.h>
int main(int argc,char*argv[])
{int n;if(argc==4){if(strcmp(argv[2],">")==0){int fd1 = open(argv[3],O_RDWR|O_CREAT|O_TRUNC,0664);if(fd1==-1){perror("open error");exit(1);}dup2(fd1,STDOUT_FILENO);}}char buf[1024];int fd2 = open(argv[1],O_RDONLY);if(fd2==-1){perror("open read error");exit(1);}while((n=read(fd2,buf,sizeof(buf)))){write(STDOUT_FILENO,buf,n);}return 0;
}