.\" Generated from openpam_readword.c by gendoc.pl
.Dd June 27, 2023
.Dt OPENPAM_READWORD 3
.Os
.Sh NAME
.Nm openpam_readword
.Nd read a word from a file, respecting shell quoting rules
.Sh SYNOPSIS
.In sys/types.h
.In stdio.h
.In security/pam_appl.h
.In security/openpam.h
.Ft "char *"
.Fn openpam_readword "FILE *f" "int *lineno" "size_t *lenp"
.Sh DESCRIPTION
The
.Fn openpam_readword
function reads the next word from a file, and
returns it in a NUL-terminated buffer allocated with
.Xr malloc 3 .
.Pp
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:
.Bl -bullet
.It
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.
.It
Within a single- or double-quoted string, all whitespace characters,
including the newline character, are preserved as-is.
.It
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.
.It
Within a single-quoted string, double quotes and backslashes are
preserved as-is.
.It
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.
.El
.Pp
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.
.Pp
If
.Fa lineno
is not
.Dv NULL ,
the integer variable it points to is
incremented every time a quoted or escaped newline character is read.
.Pp
If
.Fa lenp
is not
.Dv NULL ,
the length of the word (after quotes and
backslashes have been removed) is stored in the variable it points to.
.Sh RETURN VALUES
If successful, the
.Fn openpam_readword
function returns a pointer to a
dynamically allocated NUL-terminated string containing the first word
encountered on the line.
.Pp
The caller is responsible for releasing the returned buffer by passing
it to
.Xr free 3 .
.Pp
If
.Fn openpam_readword
reaches the end of the line or file before any
characters are copied to the word, it returns
.Dv NULL .
In the former
case, the newline is pushed back to the file.
.Pp
If
.Fn openpam_readword
reaches the end of the file while a quote or
backslash escape is in effect, it sets
.Va errno
to
.Dv EINVAL
and returns
.Dv NULL .
.Sh 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.
.Pp
.Sh SEE ALSO
.Xr openpam_readline 3 ,
.Xr openpam_readlinev 3 ,
.Xr pam 3
.Sh STANDARDS
The
.Fn openpam_readword
function is an OpenPAM extension.
.Sh AUTHORS
The
.Fn openpam_readword
function and this manual page were
developed by
.An Dag-Erling Sm\(/orgrav Aq Mt des@des.no .