The getopt() function is used to extract command line arguments. Here, we are writing a C program to demonstrators the getopt() function.

Program:

The source code to demonstrate the getopt() function is given below. The given program is compiled and executed using GCC compile on UBUNTU 18.04 OS successfully.

// C program to demonstrate the getopt() function

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

int main(int argc, char* argv[])
{
    int option = 0;

    while ((option = getopt(argc, argv, ":if:lrx")) != -1) {
        switch (option) {
        case 'i':
        case 'l':
        case 'r':
            printf("option: %c\n", option);
            break;
        case 'f':
            printf("filename: %s\n", optarg);
            break;
        case ':':
            printf("Option needs a value\n");
            break;
        case '?':
            printf("unknown option: %c\n", optopt);
            break;
        }
    }

    while (optind < argc) {
        printf("Extra arguments: %s\n", argv[optind]);
        optind++;
    }

    return 0;
}

Output:

$ gcc main.c -o  main
$ ./main -i myfile.txt -lr -x "includehelp"
option: i
option: l
option: r
extra arguments: myfile.txt
extra arguments: includehelp

Explanation:

In the main() function, we used the getopt() function to extract arguments from the command line based on given options and then printed the result on the console screen.