Linux C变成小例子——实现ls命令_linux c 变成-优快云博客

本文链接：https://blog.youkuaiyun.com/hjd_love_zzt/article/details/17715607

本文介绍了一个使用C语言编写的程序，该程序能够显示指定目录下文件的详细信息，包括权限、链接数、所有者、组、大小及最后修改时间等。通过对系统调用和库函数的应用，此程序展示了如何获取并打印文件元数据。

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/*
 * ls2.c
 *
 *  Created on: Dec 30, 2013
 *      Author: fedora
 */
#include <stdio.h>
#include <sys/types.h>
#include <dirent.h>
#include <sys/stat.h>
#include <pwd.h>
#include <grp.h>

void show_file_info(char* filename, struct stat* info_p) {
	char* uid_to_name(), *ctime(), *gid_to_name(), *filemode();
	void mode_to_letters();
	char modestr[11];

	mode_to_letters(info_p->st_mode, modestr);

	printf("%s", modestr);
	printf(" %4d", (int) info_p->st_nlink);
	printf(" %-8s", uid_to_name(info_p->st_uid));
	printf(" %-8s", gid_to_name(info_p->st_gid));
	printf(" %8ld", (long) info_p->st_size);
	printf(" %.12s", 4 + ctime(&info_p->st_mtime));
	printf(" %s\n", filename);

}

void mode_to_letters(int mode, char str[]) {
	strcpy(str, "----------");

	if (S_ISDIR(mode)) {
		str[0] = 'd';
	}

	if (S_ISCHR(mode)) {
		str[0] = 'c';
	}

	if (S_ISBLK(mode)) {
		str[0] = 'b';
	}

	if ((mode & S_IRUSR)) {
		str[1] = 'r';
	}

	if ((mode & S_IWUSR)) {
		str[2] = 'w';
	}

	if ((mode & S_IXUSR)) {
		str[3] = 'x';
	}

	if ((mode & S_IRGRP)) {
		str[4] = 'r';
	}

	if ((mode & S_IWGRP)) {
		str[5] = 'w';
	}

	if ((mode & S_IXGRP)) {
		str[6] = 'x';
	}

	if ((mode & S_IROTH)) {
		str[7] = 'r';
	}

	if ((mode & S_IWOTH)) {
		str[8] = 'w';
	}

	if ((mode & S_IXOTH)) {
		str[9] = 'x';
	}
}

char* uid_to_name(uid_t uid){
	struct passwd* getpwuid(),* pw_ptr;
	static char numstr[10];

	if((pw_ptr = getpwuid(uid)) == NULL){
	  sprintf(numstr,"%d",uid);

	  return numstr;
	}else{
		return pw_ptr->pw_name;
	}
}

char* gid_to_name(gid_t gid){
	struct group* getgrgid(),* grp_ptr;
	static char numstr[10];

	if(( grp_ptr = getgrgid(gid)) == NULL){
		sprintf(numstr,"%d",gid);
		return numstr;
	}else{
		return grp_ptr->gr_name;
	}
}
void do_ls(char dirname[]) {
	DIR* dir_ptr;
	struct dirent* direntp;

	if ((dir_ptr = opendir(dirname)) == NULL) {
		fprintf(stderr, "ls2: cannot open %s \n", dirname);
	} else {
		while ((direntp = readdir(dir_ptr)) != NULL) {
			dostat(direntp->d_name);
		}

		close(dir_ptr);
	}
}

void dostat(char* filename) {
	struct stat info;

	if (stat(filename, &info) == -1) {
		perror(filename);
	} else {
		show_file_info(filename, &info);
	}
}

int main(int ac,char* av[]){
	if(ac == 1){
		do_ls(".");
	}else{
		while(--ac){
			printf("%s: \n",*++av);
			do_ls(*av);
		}
	}
}

输出的结果如下图所示：