port/gen/getopt_long.c

/*
 * Copyright 2009 Sun Microsystems, Inc.  All rights reserved.
 * Use is subject to license terms.
 */

/*
 * Copyright (c) 2002 Todd C. Miller <Todd.Miller@courtesan.com>
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. The name of the author may not be used to endorse or promote products
 *    derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES,
 * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY
 * AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL
 * THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;
 * OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
 * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
 * OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
 * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */
/*
 * Copyright (c) 2000 The NetBSD Foundation, Inc.
 * All rights reserved.
 *
 * This code is derived from software contributed to The NetBSD Foundation
 * by Dieter Baron and Thomas Klausner.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *  This product includes software developed by the NetBSD
 *  Foundation, Inc. and its contributors.
 * 4. Neither the name of The NetBSD Foundation nor the names of its
 *  contributors may be used to endorse or promote products derived
 *  from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 */

#pragma weak _getopt_clip = getopt_clip
#pragma weak _getopt_long = getopt_long
#pragma weak _getopt_long_only = getopt_long_only

#include "lint.h"
#include <getopt.h>
#include <stdio.h>
#include <errno.h>
#include <unistd.h>
#include <stdlib.h>
#include <string.h>
#include "_libc_gettext.h"

static int optreset = 0;    /* keep track of first entry to getopt() */
#define PRINT_ERROR ((opterr) && (*options != ':'))
#define FLAG_IS_SET(flag)   ((flags & flag) != 0)   /* is flag turned on? */

/* Determine if an argument is required for this long option */
#define LONGOPT_REQUIRES_ARG(longopt) \
        ((((longopt).has_arg == optional_argument) && \
            (!FLAG_IS_SET(FLAG_OPTIONAL_ARGS))) || \
            ((longopt).has_arg == required_argument))

#define FLAG_PERMUTE    0x01    /* permute non-options to the end of argv */
#define FLAG_ALLARGS    0x02    /* treat non-options as args to option "1" */
#define FLAG_LONGONLY   0x04    /* operate as getopt_long_only() */
#define FLAG_OPTIONAL_ARGS 0x08 /* allow optional arguments to options */
#define FLAG_REQUIRE_EQUIVALENTS 0x10 /* require short<->long equivalents */
#define FLAG_ABBREV 0x20    /* long option abbreviation allowed. */
#define FLAG_W_SEMICOLON 0x40   /* Support for W; in optstring */
#define FLAG_PLUS_DASH_START 0x80   /* leading '+' or '-' in optstring */

/* return values */
#define BADCH       (int)'?'
#define BADARG      ((*options == ':') ? (int)':' : (int)'?')
#define INORDER     (int)1

#define EMSG        ""

static int getopt_internal(int, char * const *, const char *,
                const struct option *, int *, uint_t);
static int parse_long_options(int nargc, char * const *nargv, const char *,
                const struct option *, int *, int,
                uint_t flags);
static int gcd(int, int);
static void permute_args(int, int, int, char * const *);

static char *place = EMSG; /* option letter processing */

/* XXX: set optreset to 1 rather than these two */
static int nonopt_start = -1; /* first non option argument (for permute) */
static int nonopt_end = -1;   /* first option after non options (for permute) */

/*
 * Generalized error message output.
 *
 * NOTE ON ERROR MESSAGES: All the error messages in this file
 * use %s (not %c) because they are all routed through warnx_getopt(),
 * which takes a string argument. Character arguments passed
 * to warnxchar() are converted to strings automatically before
 * being passed to warnx_getopt().
 */
static void
warnx_getopt(const char *argv0, const char *msg, const char *arg) {
    char errbuf[256];
    (void) snprintf(errbuf, sizeof (errbuf), msg, argv0, arg);
    (void) write(2, errbuf, strlen(errbuf));
    (void) write(2, "\n", 1);
}

/*
 * Generalized error message output.
 */
static void
warnxchar(const char *argv0, const char *msg, const char c) {
    char charbuf[2];
    charbuf[0] = c;
    charbuf[1] = '\0';
    warnx_getopt(argv0, msg, charbuf);
}

/*
 * Generalized error message output.
 */
static void
warnxlen(const char *argv0, const char *msg, int argLen, const char *arg) {
    char argbuf[256];
    (void) strncpy(argbuf, arg, argLen);
    argbuf[argLen < (sizeof (argbuf)-1)? argLen:(sizeof (argbuf)-1)] = '\0';
    warnx_getopt(argv0, msg, argbuf);
}

/*
 * Compute the greatest common divisor of a and b.
 */
static int
gcd(int a, int b)
{
    int c;

    c = a % b;
    while (c != 0) {
        a = b;
        b = c;
        c = a % b;
    }

    return (b);
}

/*
 * Exchange the block from nonopt_start to nonopt_end with the block
 * from nonopt_end to opt_end (keeping the same order of arguments
 * in each block).
 */
static void
permute_args(int panonopt_start, int panonopt_end, int opt_end,
    char * const *nargv)
{
    int cstart, cyclelen, i, j, ncycle, nnonopts, nopts, pos;
    char *swap;

    /*
     * compute lengths of blocks and number and size of cycles
     */
    nnonopts = panonopt_end - panonopt_start;
    nopts = opt_end - panonopt_end;
    ncycle = gcd(nnonopts, nopts);
    cyclelen = (opt_end - panonopt_start) / ncycle;

    for (i = 0; i < ncycle; i++) {
        cstart = panonopt_end+i;
        pos = cstart;
        for (j = 0; j < cyclelen; j++) {
            if (pos >= panonopt_end)
                pos -= nnonopts;
            else
                pos += nopts;
            swap = nargv[pos];
            ((char **)nargv)[pos] = nargv[cstart];
            ((char **)nargv)[cstart] = swap;
        }
    }
} /* permute_args() */

/*
 * Verify that each short option (character flag) has a long equivalent,
 * and that each long option has a short option equivalent. Note that
 * multiple long options can map to the same character.
 *
 * This behavior is defined by Sun's CLIP specification (11/12/02),
 * and currently getopt_clip() is the only getopt variant that
 * requires it.
 *
 * If error output is enabled and an error is found, this function
 * prints ONE error message (the first error found) and returns an
 * error value.
 *
 * ASSUMES: options != NULL
 * ASSUMES: long_options may be NULL
 *
 * Returns < 0 if an error is found
 * Returns >= 0 on success
 */
static int
/* LINTED: argument unused in function: nargc */
verify_short_long_equivalents(int nargc,
                char *const *nargv,
                const char *options,
                const struct option *long_options,
                uint_t flags) {
    int short_i = 0;
    int long_i = 0;
    int equivFound = 0;
    int ch = 0;

    /*
     * Find a long option for each short option
     */
    equivFound = 1;
    for (short_i = 0; equivFound && (options[short_i] != 0); ++short_i) {
        ch = options[short_i];

        if (ch == ':') {
            continue;
        }
        if (FLAG_IS_SET(FLAG_W_SEMICOLON) &&
            (ch == 'W') && (options[short_i+1] == ';')) {
            /* W; is a special case */
            ++short_i;
            continue;
        }

        equivFound = 0;
        if (long_options != NULL) {
            for (long_i = 0; ((!equivFound) &&
                    (long_options[long_i].name != NULL));
                                ++long_i) {
                equivFound = (ch == long_options[long_i].val);
            }
        }
        if ((!equivFound) && (PRINT_ERROR)) {
            warnxchar(nargv[0],
                _libc_gettext(
                "%s: equivalent long option required -- %s"),
                ch);
        }
    } /* short_i */

    /*
     * Find a short option for each long option. Note that if we came
     * out of the above loop with equivFound==0, we are already done.
     */
    if (equivFound && (long_options != NULL)) {
        for (long_i = 0; (equivFound &&
                (long_options[long_i].name != NULL));
                                ++long_i) {
            equivFound = ((long_options[long_i].val != 0) &&
                (strchr(options, long_options[long_i].val)
                                != NULL));

            if ((!equivFound) && (PRINT_ERROR)) {
                warnx_getopt(nargv[0],
                    _libc_gettext(
                "%s: equivalent short option required -- %s"),
                    long_options[long_i].name);
            }
        } /* for long_i */
    }

    return (equivFound? 0:-1);
} /* verify_short_long_equivalents() */

/*
 * parse_long_options --
 *  Parse long options in argc/argv argument vector.
 * Returns -1 if short_too is set and the option does not match long_options.
 */
static int
parse_long_options(int nargc, char * const *nargv, const char *options,
    const struct option *long_options, int *idx, int short_too,
    uint_t flags)
{
    char *current_argv = NULL;
    char *argv_equal_ptr = NULL;
    size_t current_argv_len = 0;
    size_t long_option_len = 0;
    int i = 0;
    int match = 0;

    current_argv = place;
    match = -1;

    optind++;

    if ((argv_equal_ptr = strchr(current_argv, '=')) != NULL) {
        /* argument found (--option=arg) */
        current_argv_len = (argv_equal_ptr - current_argv);
        argv_equal_ptr++;
    } else {
        current_argv_len = strlen(current_argv);
    }

    for (i = 0; (long_options[i].name != NULL); i++) {

        /* find matching long option */
        if (strncmp(current_argv, long_options[i].name,
            current_argv_len) != 0) {
            continue;   /* no match  */
        }
        long_option_len = strlen(long_options[i].name);
        if ((!FLAG_IS_SET(FLAG_ABBREV)) &&
            (long_option_len > current_argv_len)) {
            continue;   /* Abbreviations are disabled */
        }

        if (long_option_len == current_argv_len) {
            /* exact match */
            match = i;
            break;
        }
        /*
         * If this is a known short option, don't allow
         * a partial match of a single character.
         */
        if (short_too && current_argv_len == 1)
            continue;

        if (match == -1)    /* partial match */
            match = i;
        else {
            /* ambiguous abbreviation */
            if (PRINT_ERROR) {
                warnxlen(nargv[0],
                    _libc_gettext(
                    "%s: ambiguous option -- %s"),
                    (int)current_argv_len,
                    current_argv);
            }
            optopt = 0;
            return (BADCH);
        }
    } /* for i */
    if (match != -1) {      /* option found */
        if ((long_options[match].has_arg == no_argument) &&
            (argv_equal_ptr != NULL)) {
            if (PRINT_ERROR) {
                warnxlen(nargv[0],
                    _libc_gettext(
                "%s: option doesn't take an argument -- %s"),
                    (int)current_argv_len,
                    current_argv);
            }
            /*
             * XXX: GNU sets optopt to val regardless of flag
             */
            if (long_options[match].flag == NULL)
                optopt = long_options[match].val;
            else
                optopt = 0;
            return (BADARG);
        }
        if (long_options[match].has_arg == required_argument ||
            long_options[match].has_arg == optional_argument) {
            if (argv_equal_ptr != NULL) {
                optarg = argv_equal_ptr;
            } else if (LONGOPT_REQUIRES_ARG(long_options[match])) {
                /* The next argv must be the option argument */
                if (optind < nargc) {
                    optarg = nargv[optind];
                }
                ++optind; /* code below depends on this */
            }
        }
        if (LONGOPT_REQUIRES_ARG(long_options[match]) &&
            (optarg == NULL)) {
            /*
             * Missing argument; leading ':' indicates no error
             * should be generated.
             */
            if (PRINT_ERROR) {
                warnx_getopt(nargv[0],
                    _libc_gettext(
                "%s: option requires an argument -- %s"),
                    current_argv);
            }
            /*
             * XXX: GNU sets optopt to val regardless of flag
             */
            if (long_options[match].flag == NULL)
                optopt = long_options[match].val;
            else
                optopt = 0;
            --optind;
            return (BADARG);
        }
    } else {            /* unknown option */
        if (short_too) {
            --optind;
            return (-1);
        }
        if (PRINT_ERROR) {
            warnx_getopt(nargv[0],
                _libc_gettext("%s: illegal option -- %s"),
                current_argv);
        }
        optopt = 0;
        return (BADCH);
    }
    if (idx)
        *idx = match;
    if (long_options[match].flag != NULL) {
        *long_options[match].flag = long_options[match].val;
        return (0);
    } else {
        optopt = long_options[match].val;
        return (optopt);
    }
} /* parse_long_options() */

/*
 * getopt_internal() --
 *  Parse argc/argv argument vector.  Called by user level routines.
 *
 * This implements all of the getopt_long(), getopt_long_only(),
 * getopt_clip() variants.
 */
static int
getopt_internal(int nargc, char * const *nargv, const char *options,
    const struct option *long_options, int *idx, uint_t flags)
{
    char *oli;              /* option letter list index */
    int optchar, short_too;
    static int posixly_correct = -1;

    if (options == NULL)
        return (-1);

    /*
     * Disable GNU extensions if POSIXLY_CORRECT is set or options
     * string begins with a '+'.
     */
    if (posixly_correct == -1) {
        posixly_correct = (getenv("POSIXLY_CORRECT") != NULL);
    }
    if (FLAG_IS_SET(FLAG_PLUS_DASH_START)) {
        /*
         * + or - at start of optstring takes precedence
         * over POSIXLY_CORRECT.
         */
        if (*options == '+') {
            /*
             * leading + means POSIX-compliant; first non-option
             * ends option list. Therefore, don't permute args.
             */
            posixly_correct = 1;
        } else if (*options == '-') {
            posixly_correct = 0;
            flags |= FLAG_ALLARGS;
        }
        if ((*options == '+') || (*options == '-')) {
            options++;
        }
    } /* if FLAG_PLUS_DASH_START */

    if (posixly_correct) {
        flags &= ~FLAG_PERMUTE;
        flags &= ~FLAG_ALLARGS;
    }

    /*
     * Some programs (like GNU cvs) set optind to 0 to restart
     * option processing. Work around this braindamage.
     *
     * The above problem comes from using global variables. We
     * should avoid their use in the future.
     */
    if (optind == 0) {
        optind = optreset = 1;
    }

    optarg = NULL;
    optopt = 0;

    if (optreset) {
        nonopt_start = nonopt_end = -1;
    }

    /*
     * On the first call, make sure that there is a short equivalent
     * for each long option, and vice versa. This is required by
     * Sun's CLIP specification (11/12/02).
     */
    if ((optind == 1) && FLAG_IS_SET(FLAG_REQUIRE_EQUIVALENTS)) {
        if (verify_short_long_equivalents(
            nargc, nargv, options, long_options, flags) < 0) {
            /* function printed any necessary messages */
            errno = EINVAL;     /* invalid argument */
            return (-1);
        }
    }

start:
    if (optreset || !*place) {      /* update scanning pointer */
        optreset = 0;
        if (optind >= nargc) {      /* end of argument vector */
            place = EMSG;
            if (nonopt_end != -1) {
                /* do permutation, if we have to */
                permute_args(nonopt_start, nonopt_end,
                    optind, nargv);
                optind -= nonopt_end - nonopt_start;

            } else if (nonopt_start != -1) {
                /*
                 * If we skipped non-options, set optind
                 * to the first of them.
                 */
                optind = nonopt_start;
            }
            nonopt_start = nonopt_end = -1;
            return (-1);
        }
        if ((*(place = nargv[optind]) != '-') || (place[1] == '\0')) {
            place = EMSG;       /* found non-option */
            if (flags & FLAG_ALLARGS) {
                /*
                 * GNU extension:
                 * return non-option as argument to option '\1'
                 */
                optarg = nargv[optind++];
                return (INORDER);
            }
            if (!(flags & FLAG_PERMUTE)) {
                /*
                 * If no permutation wanted, stop parsing
                 * at first non-option.
                 */
                return (-1);
            }
            /* do permutation */
            if (nonopt_start == -1)
                nonopt_start = optind;
            else if (nonopt_end != -1) {
                permute_args(nonopt_start, nonopt_end,
                    optind, nargv);
                nonopt_start = optind -
                    (nonopt_end - nonopt_start);
                nonopt_end = -1;
            }
            optind++;
            /* process next argument */
            goto start;
        }
        if (nonopt_start != -1 && nonopt_end == -1)
            nonopt_end = optind;

        /*
         * Check for "--" or "--foo" with no long options
         * but if place is simply "-" leave it unmolested.
         */
        if (place[1] != '\0' && *++place == '-' &&
            (place[1] == '\0' || long_options == NULL)) {
            optind++;
            place = EMSG;
            /*
             * We found an option (--), so if we skipped
             * non-options, we have to permute.
             */
            if (nonopt_end != -1) {
                permute_args(nonopt_start, nonopt_end,
                    optind, nargv);
                optind -= nonopt_end - nonopt_start;
            }
            nonopt_start = nonopt_end = -1;
            return (-1);
        }
    }

    /*
     * Check long options if:
     *  1) we were passed some
     *  2) the arg is not just "-"
     *  3) either the arg starts with -- or we are getopt_long_only()
     */
    if (long_options != NULL && place != nargv[optind] &&
        (*place == '-' || (FLAG_IS_SET(FLAG_LONGONLY)))) {
        short_too = 0;
        if (*place == '-')
            place++;        /* --foo long option */
        else if (*place != ':' && strchr(options, *place) != NULL)
            short_too = 1;      /* could be short option too */

        optchar = parse_long_options(nargc, nargv, options,
            long_options, idx, short_too, flags);
        if (optchar != -1) {
            place = EMSG;
            return (optchar);
        }
    }

    if ((optchar = (int)*place++) == (int)':' ||
        (oli = strchr(options, optchar)) == NULL) {
        /*
         * If the user didn't specify '-' as an option,
         * assume it means -1 as POSIX specifies.
         */
        if (optchar == (int)'-')
            return (-1);
        /* option letter unknown or ':' */
        if (!*place)
            ++optind;
        if (PRINT_ERROR)
            warnxchar(nargv[0],
                _libc_gettext("%s: illegal option -- %s"),
                optchar);
        optopt = optchar;
        return (BADCH);
    }
    if (FLAG_IS_SET(FLAG_W_SEMICOLON) &&
        (long_options != NULL) && (optchar == 'W') && (oli[1] == ';')) {
        /* -W long-option */
        /* LINTED: statement has no consequent: if */
        if (*place) {           /* no space */
            /* NOTHING */;
        } else if (++optind >= nargc) { /* no long-option after -W */
            place = EMSG;
            if (PRINT_ERROR)
                warnxchar(nargv[0],
                    _libc_gettext(
                "%s: option requires an argument -- %s"),
                    optchar);
            optopt = optchar;
            return (BADARG);
        } else {            /* white space */
            place = nargv[optind];
        }
        optchar = parse_long_options(
            nargc, nargv, options, long_options,
            idx, 0, flags);

        /*
         * PSARC 2003/645 - Match GNU behavior, set optarg to
         * the long-option.
         */
        if (optarg == NULL) {
            optarg = nargv[optind-1];
        }
        place = EMSG;
        return (optchar);
    }
    if (*++oli != ':') {            /* doesn't take argument */
        if (!*place)
            ++optind;
    } else {                /* takes (optional) argument */
        optarg = NULL;
        if (*place) {           /* no white space */
            optarg = place;
        /* XXX: disable test for :: if PC? (GNU doesn't) */
        } else if (!(FLAG_IS_SET(FLAG_OPTIONAL_ARGS) &&
            (oli[1] == ':'))) {
            /* arg is required (not optional) */

            if (++optind >= nargc) {    /* no arg */
                place = EMSG;
                if (PRINT_ERROR) {
                    warnxchar(nargv[0],
                        _libc_gettext(
                "%s: option requires an argument -- %s"),
                        optchar);
                }
                optopt = optchar;
                return (BADARG);
            } else
                optarg = nargv[optind];
        }
        place = EMSG;
        ++optind;
    }
    /* return valid option letter */
    optopt = optchar;       /* preserve getopt() behavior */
    return (optchar);
} /* getopt_internal() */

/*
 * getopt_long() --
 *  Parse argc/argv argument vector.
 *
 * Requires that long options be preceded with a two dashes
 * (e.g., --longoption).
 */
int
getopt_long(int nargc, char *const *nargv,
        const char *optstring,
        const struct option *long_options, int *long_index)
{

    return (getopt_internal(
        nargc, nargv, optstring, long_options, long_index,
        FLAG_PERMUTE
        | FLAG_OPTIONAL_ARGS
        | FLAG_ABBREV
        | FLAG_W_SEMICOLON
        | FLAG_PLUS_DASH_START));
} /* getopt_long() */

/*
 * getopt_long_only() --
 *  Parse argc/argv argument vector.
 *
 * Long options may be preceded with a single dash (e.g., -longoption)
 */
int
getopt_long_only(int nargc, char *const *nargv,
        const char *optstring,
        const struct option *long_options, int *long_index)
{

    return (getopt_internal(
        nargc, nargv, optstring, long_options, long_index,
        FLAG_PERMUTE
        | FLAG_OPTIONAL_ARGS
        | FLAG_ABBREV
        | FLAG_W_SEMICOLON
        | FLAG_PLUS_DASH_START
        | FLAG_LONGONLY));
} /* getopt_long_only() */

/*
 * getopt_clip() --
 *  Parse argc/argv argument vector, requiring compliance with
 *  Sun's CLIP specification (11/12/02)
 *
 * o Does not allow arguments to be optional (optional_argument is
 *   treated as required_argument).
 *
 * o Does not allow long options to be abbreviated on the command line
 *
 * o Does not allow long argument to be preceded by a single dash
 *   (Double-dash '--' is required)
 *
 * o Stops option processing at the first non-option
 *
 * o Requires that every long option have a short-option (single
 *   character) equivalent and vice-versa. If a short option or
 *   long option without an equivalent is found, an error message
 *   is printed and -1 is returned on the first call, and errno
 *   is set to EINVAL.
 *
 * o Leading + or - in optstring is ignored, and opstring is
 *   treated as if it began after the + or - .
 */
int
getopt_clip(int nargc, char *const *nargv,
        const char *optstring,
        const struct option *long_options, int *long_index)
{
    return getopt_internal(
        nargc, nargv, optstring, long_options, long_index,
        /*
         * no permutation,
         * no optional args,
         * no long-only,
         * no abbreviations
         * no support for +- at start of optstring
         * yes support for "W;" in optstring
         */
        FLAG_W_SEMICOLON
        | FLAG_REQUIRE_EQUIVALENTS);
} /* getopt_clip() */