I'm currently doing the Exploit-Exercises on level02 where in script I see a function called 'asprintf',asprintf(&buffer, "/bin/echo %s is cool" , getenv("USER")); buffer = null; before this function call.
Please explain to me in plain english what this function do and why it is there, I know that there is another post asking the same thing but it didn't help me that much. (and YES I read the man page!)
Please no ignore or question delete, it's not the 1st time, (message to the moderators).
I think the asprintf function you mention is a variant of sprintf that is specific to the glibc standard library. The first argument to the function is not a pointer to a character array, as with sprintf, but a pointer to char * variable that will hold the address of a newly-allocated char array. That is, the asprintf function does the same as sprintf but, rather than working with a fixed size char array, it allocates space for the string that it builds. The array allocated by asprintf has to be freed, at some later point, by the caller.
Apparenty you are looking for a sample usage of asprintf:
char *buffer = NULL;
if (asprintf(&buffer, "The counter is %d\n", 42) < 0)
{ perror("asprintf failed"); exit(EXIT_FAILURE); };
// now buffer points to a heap allocated string "The counter is 42\n".
printf("%s", buffer); // print the string on the terminal
free(buffer); // free the buffer allocated by `asprintf`.
