简单实现ls命令

#include <stdio.h>#include <unistd.h>#include <string.h>#include <sys/stat.h>#include <pwd.h>#include <grp.h>#include <time.h>#include <dirent.h>#include <getopt.h>#include <stdlib.h>int aflag, lflag;typedef struct _node_{char fname[256];struct _node_ *next;} linknode, *linklist;void display_file(char *path, char *fname){struct stat buf;struct tm *tp;if ( ! lflag ){printf("%s  ", fname);return;}if (lstat(path, &buf) < 0){perror("fail to lstat");return ;}switch (buf.st_mode & S_IFMT){case S_IFSOCK :printf("s");break;case S_IFLNK :printf("l");break;case S_IFREG :printf("-");break;case S_IFBLK :printf("b");break;case S_IFDIR :printf("d");break;case S_IFCHR :printf("c");break;case S_IFIFO :printf("p");break;}int n;for (n=8; n>=0; n--){if (buf.st_mode & (1 << n)){switch (n % 3){case 2 :printf("r");break;case 1 :printf("w");break;case 0 :printf("x");break;}}else{printf("-");}}printf("%3d", buf.st_nlink);printf(" %s", getpwuid(buf.st_uid)->pw_name);printf(" %s", getgrgid(buf.st_gid)->gr_name);printf("%8ld", buf.st_size);tp = localtime(&buf.st_mtime);printf(" %d", tp->tm_year+1900);if (tp->tm_mon < 9) printf("-0%d", tp->tm_mon+1);else printf("-%d", tp->tm_mon+1);if (tp->tm_mday < 10) printf("-0%d ", tp->tm_mday);else printf("-%d ", tp->tm_mday);if (tp->tm_min < 10) printf("0%d", tp->tm_min);else printf("%d", tp->tm_min);if (tp->tm_sec < 10) printf(":0%d ", tp->tm_sec);else printf(":%d ", tp->tm_sec);printf("%s\n", fname);return;}void display_dir(char *dirname){DIR *mydir;struct dirent *myitem;char path[256];linklist h, p, q;h = (linklist)malloc(sizeof(linknode));h->next = NULL;mydir = opendir(dirname);while((myitem = readdir(mydir)) != NULL){if ((myitem->d_name[0] == '.') && !aflag)  continue;p = h;while ((p->next != NULL) && (strcmp(p->next->fname, myitem->d_name) < 0)) p = p->next;q = (linklist)malloc(sizeof(linknode));strcpy(q->fname, myitem->d_name);q->next = p->next;p->next = q;}p = h->next;while ( p ){sprintf(path, "%s/%s", dirname, p->fname);display_file(path, p->fname);p = p->next;}return;}int main(int argc, char *argv[]){struct stat buf;int i, ch;opterr = 0;while ((ch = getopt(argc, argv, "la")) != EOF){switch ( ch ){case 'a' : aflag = 1; break;case 'l' : lflag = 1; break;default  : printf("wrong option %d is set\n", optopt); return -1;}}if (optind == argc){display_dir(".");if ( ! lflag ) printf("\n");return 0;}for (i=optind; i<argc; i++){if (lstat(argv[i], &buf) < 0){perror("fail to lstat");return -1;}if ( S_ISDIR(buf.st_mode) ){printf("%s:\n", argv[i]);display_dir(argv[i]);}else{display_file(argv[i], argv[i]);}}return 0;}

运行：./a.out -la   ./a.out / 

shell命令其实也是调用系统函数。这些系统函数调用好的话你也可以实现shell命令。。敬请参考《UNIX环境高级编程2》，他可以让你深刻了解linux系统。随手可以自己去写shell命令。