ed.c

#include <stdlib.h>
#include <stdio.h>
#include <string.h>
 
#ifndef ED_VERSION
# define ED_VERSION "1.0"
#endif /* !ED_VERSION */
 
#define IS_OPTARG(a, s, l) a[1] == s || \
                     strcmp(a + 1, "-" l) == 0
 
static const char *prg_name;
 
void
version(void)
{
    printf("%s v%s\n", prg_name, ED_VERSION);
    printf("Copyright (C) 2022 d0p1\n");
    printf("License BSD-3: <https://directory.fsf.org/wiki/License:BSD-3-Clause>\n");
    printf("This is free software: you are free to change and redistribute it.\n");
    printf("There is NO WARRANTY, to the extent permitted by law.\n");
    exit(EXIT_SUCCESS);
}
 
void
usage(FILE *out, int retval)
{
    fprintf(out, "Usage: %s [OPTION]... [FILE]\n\n", prg_name);
    fprintf(out, "Options:\n");
    fprintf(out, "\t-h, --help\tdisplay this help and exit\n");
    fprintf(out, "\t-V, --version\toutput version information and exit\n");
 
    exit(retval);
}
 
size_t
parse_flags(int argc, char *const argv[])
{
    int idx;
 
    for (idx = 0; idx < argc; idx++)
    {
        if (argv[idx][0] == '-')
        {
            if (IS_OPTARG(argv[idx], 'h', "help"))
            {
                usage(stdout, EXIT_SUCCESS);
            }
            else if (IS_OPTARG(argv[idx], 'V', "version"))
            {
                version();
            }
            else
            {
                usage(stderr, EXIT_FAILURE);
            }
        }
        else
        {
            break;
        }
    }
 
    if (idx >= argc)
    {
        usage(stderr, EXIT_FAILURE);
    }
 
    return (idx);
}
 
int
main(int argc, char *const argv[])
{
    size_t idx;
 
    prg_name = *argv++; /* save and skip program name */
    argc--;
 
    idx = parse_flags(argc, argv);
    (void)idx;
    return (EXIT_SUCCESS);
}