getopt_example.c

#include <stdio.h>
#include <unistd.h>

int main (int argc, char *argv[]) {
int opt = 0;
char *in_fname = NULL;
char *out_fname = NULL;

while ((opt = getopt(argc, argv, "i:o:")) != -1) {
    switch(opt) {
    case 'i':
    in_fname = optarg;
    printf("\nInput option value=%s", in_fname);
    break;
    case 'o':
    out_fname = optarg;
    printf("\nOutput option value=%s", out_fname);
    break;
    case '?':
    /* Case when user enters the command as
     * $ ./cmd_exe -i
     */
    if (optopt == 'i') {
    printf("\nMissing mandatory input option");
    /* Case when user enters the command as
     * # ./cmd_exe -o
     */
  } else if (optopt == 'o') {
     printf("\nMissing mandatory output option");
  } else {
     printf("\nInvalid option received");
  }
  break;
 }
 }

printf("\n");
return 0;
 }