NetBSD/lib/libc/gen/getcwd.3

.\"	$NetBSD: getcwd.3,v 1.18 2010/04/29 06:54:26 jruoho Exp $
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.\"     @(#)getcwd.3	8.2 (Berkeley) 12/11/93
.\"
.Dd April 29, 2010
.Dt GETCWD 3
.Os
.Sh NAME
.Nm getcwd ,
.Nm getwd
.Nd get working directory pathname
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In unistd.h
.Ft char *
.Fn getcwd "char *buf" "size_t size"
.Ft char *
.Fn getwd "char *buf"
.Sh DESCRIPTION
The
.Fn getcwd
function copies the absolute pathname of the current working directory
into the memory referenced by
.Fa buf
and returns a pointer to
.Fa buf .
The
.Fa size
argument is the size, in bytes, of the array referenced by
.Fa buf .
.Pp
If
.Fa buf
is
.Dv NULL ,
space is allocated as necessary to store the pathname.
This space may later be
.Xr free 3 Ns 'd .
.Pp
The function
.Fn getwd
is a compatibility routine which calls
.Fn getcwd
with its
.Fa buf
argument and a size of
.Dv MAXPATHLEN
(as defined in the include
file
.In sys/param.h ) .
Obviously,
.Fa buf
should be at least
.Dv MAXPATHLEN
bytes in length.
.Pp
These routines have traditionally been used by programs to save the
name of a working directory for the purpose of returning to it.
A much faster and less error-prone method of accomplishing this is to
open the current directory
.Pq Ql \&.
and use the
.Xr fchdir 2
function to return.
.Sh RETURN VALUES
Upon successful completion, a pointer to the pathname is returned.
Otherwise a
.Dv NULL
pointer is returned and the global variable
.Va errno
is set to indicate the error.
In addition,
.Fn getwd
copies the error message associated with
.Va errno
into the memory referenced by
.Fa buf .
.Sh ERRORS
The
.Fn getcwd
function
will fail if:
.Bl -tag -width Er
.It Bq Er EACCES
Read or search permission was denied for a component of the pathname.
.It Bq Er EINVAL
The
.Fa size
argument is zero.
.It Bq Er ENOENT
A component of the pathname no longer exists.
.It Bq Er ENOMEM
Insufficient memory is available.
.It Bq Er ERANGE
The
.Fa size
argument is greater than zero but smaller than the length of the pathname
plus 1.
.El
.Sh SEE ALSO
.Xr chdir 2 ,
.Xr fchdir 2 ,
.Xr malloc 3 ,
.Xr strerror 3
.Sh STANDARDS
The
.Fn getwd
and
.Fn getcwd
functions conform to
.St -p1003.1-90 .
The
.St -p1003.1-2004
revision marked
.Fn getwd
as legacy and recommended the use of
.Fn getcwd
instead.
The
.St -p1003.1-2008
revision removed
.Fn getwd
from the specification.
.Pp
The ability to specify a
.Dv NULL
pointer and have
.Fn getcwd
allocate memory as necessary is an extension.
.Sh HISTORY
The
.Fn getwd
function appeared in
.Bx 4.0 .
.Sh SECURITY CONSIDERATIONS
As
.Fn getwd
does not know the length of the supplied buffer, it is possible
for a long (but valid) path to overflow the buffer and provide
a means for an attacker to exploit the caller.
.Fn getcwd
should be used in place of
.Fn getwd
(the latter is only provided for compatibility purposes).