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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(): _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 non-
       zero.

       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).

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 3.15 of the Linux man-pages project.  A
       description of the project, and information about reporting  bugs,  can
       be found at http://www.kernel.org/doc/man-pages/.