C Program to Save output of system command to variable with popen

How to write a C Program to Save output of system command to variable with popen ?

Solution:

C Program to Realization On The Unix Tail Command

How to write a C Program to  Realization On The Unix Tail Command in C Programming Language ?

Solution For C Program :

Return the number of tokens given a command

C Program Return the number of tokens given a command

1. /* in setup_stack()... */  
2.  
3.   int i = 0;
4.   int argc = get_argc(file_name);
5.   char *token, *save_ptr;
6.   char **argv = malloc((argc + 1) * sizeof(char *));
7.   size_t token_size;
8.  

9.   //generate argv and push args onto stack

10.   for (token = strtok_r((char *)file_name, " ", &save_ptr); token != NULL; token = strtok_r(NULL, " ", &save_ptr)) {
11.     token_size = strlen(token) + 1;
12.     *esp = *esp - token_size;
13.     argv[i] = *esp;
14.     i++;
15.     memcpy(*esp, token, token_size);
16.   } argv[argc] = 0;
17.  

18.   //perform alignment

19.   size_t alignment = (size_t) *esp % 4;
20.   if (alignment) {
21.     *esp = *esp - alignment;
22.     memcpy(*esp, &argv[argc], alignment);
23.   }
24.  

25.   //push argv pointers

26.   for (i = argc; i >= 0; i--) {
27.     *esp = *esp - sizeof(char *);
28.     memcpy(*esp, &argv[i], sizeof(char *));
29.   }
30.  

31.   //push pointer to argv

32.   char *ptr = *esp;
33.   *esp = *esp - sizeof(char **);
34.   memcpy(*esp, &ptr, sizeof(char **));
35.  
36.   //push argc
37.   *esp = *esp - sizeof(int);
38.   memcpy(*esp, &argc, sizeof(int));
39.  

40.  //push dummy return address

41.   *esp = *esp - sizeof(void *);
42.   memcpy(*esp, &argv[argc], sizeof(void *));
43.  
44.   free(argv);
45.   return success;
46. }
47.  

48. /* Return the number of tokens given a command 'file_name.' */

49. int get_argc(const char* file_name) {
50.     int argc = 0;
51.     char *buffer, *token, *save_ptr;
52.     buffer = malloc(sizeof(file_name));
53.     strlcpy(buffer, file_name, sizeof(file_name));
54.     for (token = strtok_r((char *)buffer, " ", &save_ptr); token != NULL; token = strtok_r(NULL, " ", &save_ptr)) {
55.         argc++;
56.     }
57.     free(buffer);
58.     return argc;
59. }