====== getopt(): Parse command-line opions ======

  * [[https://www.gnu.org/software/libc/manual/html_node/Getopt.html|Parsing program options using getopt]]
  * [[https://man7.org/linux/man-pages/man3/getopt.3.html|getopt(3) — Linux manual page]]
  * [[https://azrael.digipen.edu/~mmead/www/mg/getopt/index.html|Mead's Guide to getopt]]

----
===== Simple Usage =====

<code C>
// man 3 getopt
// gcc -Wall -Wextra -Werror -pedantic -std=c99 getopt.c

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

int main(int argc, char *argv[])
{
    int opt;
    while ((opt = getopt(argc, argv, "abX")) != -1) {
        switch (opt) {
            case 'a':
                printf("Option -a provided\n");
                break;
            case 'b':
                printf("Option -b provided\n");
                break;
            case 'X':
                printf("Option -X provided\n");
                break;
        }
    }
    return EXIT_SUCCESS;
}
</code>

<code>
$ ./a.out -b
Option -b provided

$ ./a.out -b -X -a
Option -b provided
Option -X provided
Option -a provided

$ ./a.out -bXa
Option -b provided
Option -X provided
Option -a provided

$ ./a.out -a b X
Option -a provided

$ ./a.out -t
./a.out: invalid option -- 't'

$ ./a.out a b c

</code>

<code C>
// Option Arguments
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <getopt.h>

int main(int argc, char *argv[])
{
    int opt;
    while ((opt = getopt(argc, argv, "a:b:X")) != -1) {
        switch (opt) {
            case 'a':
                printf("Option -a provided with argument: %s\n", optarg);
                break;
            case 'b':
                printf("Option -b provided with argument: %s\n", optarg);
                break;
            case 'X':
                printf("Option -X provided\n");
                break;
        }
    }
    return EXIT_SUCCESS;
}
</code>

<code>
$ gcc -Wall -Wextra -Werror -pedantic -std=c99 getopt.c

$ ./a.out -a one -b two -X
Option -a provided with argument: one
Option -b provided with argument: two
Option -X provided

$ ./a.out -aone -btwo
Option -a provided with argument: one
Option -b provided with argument: two

$ ./a.out -X -a
Option -X provided
./a.out: option requires an argument -- 'a'

$ ./a.out -a -X
Option -a provided with argument: -X
</code>

<code C>

// Unknown Options and Missing Option Arguments

// To disable the automatic error printing, simply put a colon as
// the first character in optstring

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

int main(int argc, char *argv[])
{
    int opt;
    // Notice the leading : in the option string
    while ((opt = getopt(argc, argv, ":a:b:X")) != -1) {
        switch (opt) {
            case 'a':
                printf("Option -a provided with argument: %s\n", optarg);
                break;
            case 'b':
                printf("Option -b provided with argument: %s\n", optarg);
                break;
            case 'X':
                printf("Option -X provided\n");
                break;
            case '?':
                printf("Unknown option: %c\n", optopt);
                break;
            case ':':
                printf("Missing argument for: %c\n", optopt);
                break;
        }
    }
    return EXIT_SUCCESS;
}

</code>

<code>
$ gcc -Wall -Wextra -Werror -pedantic -std=c99 getopt.c

$ ./a.out -a
Missing argument for: a

$ ./a.out -t
Unknown option: t

$ ./a.out -a one -t -X -b
Option -a provided with argument: one
Unknown option: t
Option -X provided
Missing argument for: b

$ ./a.out -a one,two,three
Option -a provided with argument: one,two,three

$ ./a.out -a "one two three"
Option -a provided with argument: one two three
</code>


<code C>
// Non-Option Arguments

// The default is to permute the contents of argv while scanning it
// so that eventually all the non-options are at the end. This allows
// options to be given in any order, even with programs that were not
// written to expect this.

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

int main(int argc, char *argv[])
{
    int opt;

    // Notice the leading : in the option string
    while ((opt = getopt(argc, argv, ":a:b:X")) != -1) {
        switch (opt) {
            case 'a':
                printf("Option -a provided with argument: %s\n", optarg);
                break;
            case 'b':
                printf("Option -b provided with argument: %s\n", optarg);
                break;
            case 'X':
                printf("Option -X provided\n");
                break;
            case '?':
                printf("Unknown option: %c\n", optopt);
                break;
            case ':':
                printf("Missing argument for: %c\n", optopt);
                break;
        }
    }

    if (optind < argc) {
        printf("Non-option args: ");
        while (optind < argc)
            printf("%s ", argv[optind++]);
        printf("\n");
    }

    return EXIT_SUCCESS;
}
</code>

<code>
$ ./a.out x -a one y -X z
Option -a provided with argument: one
Option -X provided
Non-option args: x y z

$ ./a.out x y z -a one -b two
Option -a provided with argument: one
Option -b provided with argument: two
Non-option args: x y z
</code>

<code C>
// Non-Option Arguments

// If the options argument string begins with a hyphen (‘-’), this is
// treated specially. It permits arguments that are not options to be
// returned as if they were associated with option character ‘\1’.

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

int main(int argc, char *argv[])
{
    int opt;

    // Notice the leading minus sign - in the option string below
    // Remember that the number one in single quotes '1' is not the
    // same as the number one without quotes. '1' is ASCII 49
    while ((opt = getopt(argc, argv, "-:a:b:X")) != -1) {
        switch (opt) {
            case 'a':
                printf("Option -a provided with argument: %s\n", optarg);
                break;
            case 'b':
                printf("Option -b provided with argument: %s\n", optarg);
                break;
            case 'X':
                printf("Option -X provided\n");
                break;
            case '?':
                printf("Unknown option: %c\n", optopt);
                break;
            case ':':
                printf("Missing argument for: %c\n", optopt);
                break;
            case 1:
                printf("Non-option arg: %s\n", optarg);
                break;
        }
    }

    return EXIT_SUCCESS;
}
</code>

<code>
$ gcc -Wall -Wextra -Werror -pedantic -std=c99 getopt.c

$ ./a.out x y z -a foo
Non-option arg: x
Non-option arg: y
Non-option arg: z
Option -a provided with argument: foo

$ ./a.out x -a foo y -b bar z -X w
Non-option arg: x
Option -a provided with argument: foo
Non-option arg: y
Option -b provided with argument: bar
Non-option arg: z
Option -X provided
Non-option arg: w

$ ./a.out -t x -a foo -M y -b bar z -X w -b
Unknown option: t
Non-option arg: x
Option -a provided with argument: foo
Unknown option: M
Non-option arg: y
Option -b provided with argument: bar
Non-option arg: z
Option -X provided
Non-option arg: w
Missing argument for: b
</code>

----
===== POSIX Non-Option Arguments =====

<code C>
// Non-Option Arguments

// POSIX demands the following behavior: the first non-option stops option
// processing. This mode is selected by either setting the environment
// variable POSIXLY_CORRECT or beginning the options argument string
// with a plus sign (‘+’).

// Pejman:
// POSIXLY_CORRECT did not change anything
//#define POSIXLY_CORRECT 
// this line changed the behavior to POSIX
#define _XOPEN_SOURCE 

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

int main(int argc, char *argv[])
{
    int opt;

    // Notice the leading : in the option string
    while ((opt = getopt(argc, argv, ":a:b:X")) != -1) {  // or simply use "+:a:b:X"
        switch (opt) {
            case 'a':
                printf("Option -a provided with argument: %s\n", optarg);
                break;
            case 'b':
                printf("Option -b provided with argument: %s\n", optarg);
                break;
            case 'X':
                printf("Option -X provided\n");
                break;
            case '?':
                printf("Unknown option: %c\n", optopt);
                break;
            case ':':
                printf("Missing argument for: %c\n", optopt);
                break;
        }
    }

    if (optind < argc) {
        printf("Non-option args: ");
        while (optind < argc)
            printf("%s ", argv[optind++]);
        printf("\n");
    }

    return EXIT_SUCCESS;
}

</code>

<code>
$ gcc -Wall -Wextra -Werror -pedantic -std=c99 getopt.c

$ ./a.out x -a one y -X
Non-option args: x -a one y -X

$ ./a.out x y z -a one -b two
Non-option args: x y z -a one -b two

$ ./a.out -a one -b two x y z
Option -a provided with argument: one
Option -b provided with argument: two
Non-option args: x y z
</code>