getpwent.3

操作系统设计与实现源码

.TH GETPWENT 3
.SH NAME
getpwent, getpwnam, getpwuid, setpwent, endpwent, setpwfile \- password file routines
.SH SYNOPSIS
.ft B
.nf
#include <pwd.h>

struct passwd *getpwent(void)
struct passwd *getpwnam(const char *\fIname\fP)
struct passwd *getpwuid(uid_t \fIuid\fP)
int setpwent(void)
void endpwent(void)
void setpwfile(const char *\fIfile\fP)
.fi
.ft P
.SH DESCRIPTION
These functions are used to obtain information from the password file.  They
return this information in a
.B struct passwd
as defined by <pwd.h>:
.PP
.nf
.ta +4n +6n +15n
struct passwd {
	char	*pw_name;	/* login name */
	char	*pw_passwd;	/* encrypted password */
	uid_t	pw_uid;	/* numeric user id */
	gid_t	pw_gid;	/* numeric group id */
	char	*pw_gecos;	/* user full name and other info */
	char	*pw_dir;	/* user's home directory */
	char	*pw_shell;	/* name of the user's shell */
};
.fi
.PP
.B Getpwent()
reads the password file entry by entry.
.B Getpwnam()
scans the entire password file for the user with the given
.IR name .
.B Getpwuid()
looks for the first user with the given
.IR uid .
The
.B setpwent()
and
.B endpwent()
functions are used to open and later close the password file.  With
.B setpwfile()
one can specify the file to read other than the normal password file.  This
only sets the name, the next
.B setpwent()
call will open the file.  Do not touch the file name while it is active.
Use
.B setpwfile(NULL)
to revert back to the normal password file.
.PP
The usual way to scan the password file is (error checking omitted):
.PP
.RS
.nf
.DT
setpwent();
while ((pw = getpwent()) != NULL)
	if (appropriate_test(pw)) break;
endpwent();
.fi
.RE
.PP
The
.B pw
variable contains the entry that is wanted if non-NULL.  The
.B getpwnam()
and
.B getpwuid()
functions are implemented as in this example, with error checking of course.
.PP
.B Getpwent()
calls
.B setpwent()
if this has not yet been done.
.B Setpwent()
first calls
.B endpwent()
if the password file is still open.  (Other implementations may simply
rewind the file.)
.SH FILES
.TP 15
.B /etc/passwd
The password file database.
.SH "SEE ALSO"
.BR cuserid (3),
.BR getlogin (3),
.BR getgrent (3),
.BR passwd (5).
.SH DIAGNOSTICS
.B Setpwent()
has the same return value and error codes as the
.BR open (2)
call it uses to open the password file.  The
.BI get xxx ()
functions return NULL on end of file, entry not found, or error.  You can
set
.B errno
to zero before the call and check it after.
.SH NOTES
All
.BI get xxx ()
routines return a pointer to static storage that is overwritten in each call.
.PP
Only
.B getpwnam()
and
.B getpwuid()
are defined by \s-2POSIX\s+2.  The
.B _MINIX_SOURCE
macro must be defined before including <pwd.h> to make the other functions
visible.  The
.B pw_passwd
and
.B pw_gecos
fields are also not defined by \s-2POSIX\s+2, but are always visible.
Portable code cannot reliably detect errors by setting
.B errno
to zero.  Under Minix it is better to make a
.B getpwent()
scan if you need to look up several user-id's or names, but portable code
had better use several
.B getpwuid()
or
.B getpwnam()
calls.  The
.B getpwent()
is usually available on other systems, but may be very expensive.
.SH AUTHOR
Kees J. Bot ([e-mail])