NAME

       rpmatch - determine if the answer to a question is affirmative or negative

SYNOPSIS

       #include <stdlib.h>

       int rpmatch(const char *response);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       rpmatch():
           Since glibc 2.19:
               _DEFAULT_SOURCE
           Glibc 2.19 and earlier:
               _SVID_SOURCE

DESCRIPTION

       rpmatch()   handles   a   user   response  to  yes  or  no  questions,  with  support  for
       internationalization.

       response should be a null-terminated string containing a user-supplied  response,  perhaps
       obtained with fgets(3) or getline(3).

       The  user's  language preference is taken into account per the environment variables LANG,
       LC_MESSAGES, and LC_ALL, if the program has called setlocale(3) to effect their changes.

       Regardless of the locale, responses matching ^[Yy] are always accepted as affirmative, and
       those matching ^[Nn] are always accepted as negative.

RETURN VALUE

       After examining response, rpmatch() returns 0 for a recognized negative response ("no"), 1
       for a recognized positive  response  ("yes"),  and  -1  when  the  value  of  response  is
       unrecognized.

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.

       rpmatch() can fail for any of the reasons that regcomp(3)  or  regexec(3)  can  fail;  the
       cause  of  the error is not available from errno or anywhere else, but indicates a failure
       of the regex engine (but this case is indistinguishable from that of an unrecognized value
       of response).

ATTRIBUTES

       For an explanation of the terms used in this section, see attributes(7).

       ┌──────────┬───────────────┬────────────────┐
       │Interface │ Attribute     │ Value          │
       ├──────────┼───────────────┼────────────────┤
       │rpmatch() │ Thread safety │ MT-Safe locale │
       └──────────┴───────────────┴────────────────┘

CONFORMING TO

       rpmatch() is not required by any standard, but is available on a few other systems.

BUGS

       The  rpmatch()  implementation  looks  at  only  the  first  character  of response.  As a
       consequence, "nyes" returns 0, and "ynever; not in a million years" returns 1.   It  would
       be  preferable to accept input strings much more strictly, for example (using the extended
       regular expression notation described in regex(7)): ^([yY]|yes|YES)$ and ^([nN]|no|NO)$.

EXAMPLE

       The following program displays the results when rpmatch() is applied to the  string  given
       in the program's command-line argument.

       #define _SVID_SOURCE
       #include <locale.h>
       #include <stdlib.h>
       #include <string.h>
       #include <stdio.h>

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

           setlocale(LC_ALL, "");
           printf("rpmatch() returns: %d\n", rpmatch(argv[1]));
           exit(EXIT_SUCCESS);
       }

SEE ALSO

       fgets(3), getline(3), nl_langinfo(3), regcomp(3), setlocale(3)

COLOPHON

       This  page  is  part of release 5.05 of the Linux man-pages project.  A description of the
       project, information about reporting bugs, and the latest version of  this  page,  can  be
       found at https://www.kernel.org/doc/man-pages/.