Updated: 2022/Sep/29

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OPENPAM_READWORD(3)        Library Functions Manual        OPENPAM_READWORD(3)

NAME
     openpam_readword - read a word from a file, respecting shell quoting
     rules

SYNOPSIS
     #include <sys/types.h>
     #include <stdio.h>
     #include <security/pam_appl.h>
     #include <security/openpam.h>

     char *
     openpam_readword(FILE *f, int *lineno, size_t *lenp);

DESCRIPTION
     The openpam_readword() function reads the next word from a file, and
     returns it in a NUL-terminated buffer allocated with malloc(3).

     A word is a sequence of non-whitespace characters.  However, whitespace
     characters can be included in a word if quoted or escaped according to
     the following rules:

     ⊕   An unescaped single or double quote introduces a quoted string, which
         ends when the same quote character is encountered a second time.  The
         quotes themselves are stripped.

     ⊕   Within a single- or double-quoted string, all whitespace characters,
         including the newline character, are preserved as-is.

     ⊕   Outside a quoted string, a backslash escapes the next character,
         which is preserved as-is, unless that character is a newline, in
         which case it is discarded and reading continues at the beginning of
         the next line as if the backslash and newline had not been there.  In
         all cases, the backslash itself is discarded.

     ⊕   Within a single-quoted string, double quotes and backslashes are
         preserved as-is.

     ⊕   Within a double-quoted string, a single quote is preserved as-is, and
         a backslash is preserved as-is unless used to escape a double quote.

     In addition, if the first non-whitespace character on the line is a hash
     character (#), the rest of the line is discarded.  If a hash character
     occurs within a word, however, it is preserved as-is.  A backslash at the
     end of a comment does cause line continuation.

     If lineno is not NULL, the integer variable it points to is incremented
     every time a quoted or escaped newline character is read.

     If lenp is not NULL, the length of the word (after quotes and backslashes
     have been removed) is stored in the variable it points to.

RETURN VALUES
     If successful, the openpam_readword() function returns a pointer to a
     dynamically allocated NUL-terminated string containing the first word
     encountered on the line.

     The caller is responsible for releasing the returned buffer by passing it
     to free(3).

     If openpam_readword() reaches the end of the line or file before any
     characters are copied to the word, it returns NULL.  In the former case,
     the newline is pushed back to the file.

     If openpam_readword() reaches the end of the file while a quote or
     backslash escape is in effect, it sets errno to EINVAL and returns NULL.

IMPLEMENTATION NOTES
     The parsing rules are intended to be equivalent to the normal POSIX shell
     quoting rules.  Any discrepancy is a bug and should be reported to the
     author along with sample input that can be used to reproduce the error.

SEE ALSO
     openpam_readline(3), openpam_readlinev(3), pam(3)

STANDARDS
     The openpam_readword() function is an OpenPAM extension.

AUTHORS
     The openpam_readword() function and this manual page were developed by
     Dag-Erling Sm/orgrav <des@des.no>.

NetBSD 10.99                     June 27, 2023                    NetBSD 10.99