1 extern int cat_main(int argc, char **argv)
 2 {
 3     int status = EXIT_SUCCESS;
 4 
 5     if (argc == 1) {
 6         print_file(stdin);
 7         return status;
 8     }
 9 
10     while (--argc > 0) {
11         if(!(strcmp(*++argv, "-"))) {
12             print_file(stdin);
13         } else if (print_file_by_name(*argv) == FALSE) {
14             status = EXIT_FAILURE;
15         }
16     }
17     return status;
18 }

1 extern void print_file(FILE *file)
2 {
3     fflush(stdout);
4     copyfd(fileno(file), fileno(stdout));//将file文件的内容拷贝到stdout
5     fclose(file);
6 }

V658tekiMacBook-Pro:busybox-0.60.3 neilhappy$ cat -
input--stdin
input--stdin

1 extern int print_file_by_name(char *filename)
 2 {
 3     struct stat statBuf;
 4     int status = TRUE;
 5 
 6     if(is_directory(filename, TRUE, &statBuf)==TRUE) {
 7         error_msg("%s: Is directory", filename);
 8         status = FALSE;
 9     } else {
10         FILE *f = wfopen(filename, "r");
11         if(f!=NULL)
12             print_file(f);
13         else
14             status = FALSE;
15     }
16 
17     return status;
18 }

 1 int is_directory(const char *fileName, const int followLinks, struct stat *statBuf)
 2 {
 3     int status;
 4     int didMalloc = 0;
 5 
 6     if (statBuf == NULL) {
 7         statBuf = (struct stat *)xmalloc(sizeof(struct stat));
 8         ++didMalloc;
 9     }
10 
11     if (followLinks == TRUE)
12         status = stat(fileName, statBuf);
13     else
14         status = lstat(fileName, statBuf);
15 
16     if (status < 0 || !(S_ISDIR(statBuf->st_mode))) {
17         status = FALSE;
18     }
19     else status = TRUE;
20 
21     if (didMalloc) {
22         free(statBuf);
23         statBuf = NULL;
24     }
25     return status;
26 }