'\" t
.\" Copyright (C) 2006 Justin Pryzby <pryzbyj@justinpryzby.com>
.\"
.\" %%%LICENSE_START(PERMISSIVE_MISC)
.\" Permission is hereby granted, free of charge, to any person obtaining
.\" a copy of this software and associated documentation files (the
.\" "Software"), to deal in the Software without restriction, including
.\" without limitation the rights to use, copy, modify, merge, publish,
.\" distribute, sublicense, and/or sell copies of the Software, and to
.\" permit persons to whom the Software is furnished to do so, subject to
.\" the following conditions:
.\"
.\" The above copyright notice and this permission notice shall be
.\" included in all copies or substantial portions of the Software.
.\"
.\" THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
.\" EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
.\" MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
.\" IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
.\" CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
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.\" SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
.\" %%%LICENSE_END
.\"
.\" References:
.\"   glibc manual and source
.\"
.\" 2006-05-19, mtk, various edits and example program
.\"
.TH rpmatch 3 2023-03-30 "Linux man-pages 6.04"
.SH NAME
rpmatch \- determine if the answer to a question is affirmative or negative
.SH LIBRARY
Standard C library
.RI ( libc ", " \-lc )
.SH SYNOPSIS
.nf
.B #include <stdlib.h>
.PP
.BI "int rpmatch(const char *" response );
.fi
.PP
.RS -4
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.RE
.PP
.BR rpmatch ():
.nf
    Since glibc 2.19:
        _DEFAULT_SOURCE
    glibc 2.19 and earlier:
        _SVID_SOURCE
.fi
.SH DESCRIPTION
.BR rpmatch ()
handles a user response to yes or no questions, with
support for internationalization.
.PP
.I response
should be a null-terminated string containing a
user-supplied response, perhaps obtained with
.BR fgets (3)
or
.BR getline (3).
.PP
The user's language preference is taken into account per the
environment variables
.BR LANG ,
.BR LC_MESSAGES ,
and
.BR LC_ALL ,
if the program has called
.BR setlocale (3)
to effect their changes.
.PP
Regardless of the locale, responses matching
.B \[ha][Yy]
are always accepted as affirmative, and those matching
.B \[ha][Nn]
are always accepted as negative.
.SH RETURN VALUE
After examining
.IR response ,
.BR rpmatch ()
returns 0 for a recognized negative response ("no"), 1
for a recognized positive response ("yes"), and \-1 when the value
of
.I response
is unrecognized.
.SH ERRORS
A return value of \-1 may indicate either an invalid input, or some
other error.
It is incorrect to only test if the return value is nonzero.
.PP
.BR rpmatch ()
can fail for any of the reasons that
.BR regcomp (3)
or
.BR regexec (3)
can fail; the cause of the error
is not available from
.I errno
or anywhere else, but indicates a
failure of the regex engine (but this case is indistinguishable from
that of an unrecognized value of
.IR response ).
.SH ATTRIBUTES
For an explanation of the terms used in this section, see
.BR attributes (7).
.ad l
.nh
.TS
allbox;
lbx lb lb
l l l.
Interface	Attribute	Value
T{
.BR rpmatch ()
T}	Thread safety	MT-Safe locale
.TE
.hy
.ad
.sp 1
.SH STANDARDS
None.
.SH HISTORY
GNU, FreeBSD, AIX.
.SH BUGS
The
.BR YESEXPR " and " NOEXPR
of some locales (including "C") only inspect the first character of the
.IR response .
This can mean that "yno" et al. resolve to
.BR 1 .
This is an unfortunate historical side-effect which should be fixed in time
with proper localisation, and should not deter from
.BR rpmatch ()
being the proper way to distinguish between binary answers.
.SH EXAMPLES
The following program displays the results when
.BR rpmatch ()
is applied to the string given in the program's command-line argument.
.PP
.\" SRC BEGIN (rpmatch.c)
.EX
#define _DEFAULT_SOURCE
#include <locale.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int
main(int argc, char *argv[])
{
    if (argc != 2 || strcmp(argv[1], "\-\-help") == 0) {
        fprintf(stderr, "%s response\en", argv[0]);
        exit(EXIT_FAILURE);
    }

    setlocale(LC_ALL, "");
    printf("rpmatch() returns: %d\en", rpmatch(argv[1]));
    exit(EXIT_SUCCESS);
}
.EE
.\" SRC END
.SH SEE ALSO
.BR fgets (3),
.BR getline (3),
.BR nl_langinfo (3),
.BR regcomp (3),
.BR setlocale (3)