.\" Copyright (c) 1994
.\"	The Regents of the University of California.  All rights reserved.
.\"
.\" This code is derived from software contributed to Berkeley by
.\" Jan-Simon Pendry.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\"    notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\"    notice, this list of conditions and the following disclaimer in the
.\"    documentation and/or other materials provided with the distribution.
.\" 3. Neither the name of the University nor the names of its contributors
.\"    may be used to endorse or promote products derived from this software
.\"    without specific prior written permission.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.\"	$OpenBSD: realpath.3,v 1.26 2021/10/13 15:04:53 kn Exp $
.\"
.Dd $Mdocdate: October 13 2021 $
.Dt REALPATH 3
.Os
.Sh NAME
.Nm realpath
.Nd returns the canonicalized absolute pathname
.Sh SYNOPSIS
.In limits.h
.In stdlib.h
.Ft "char *"
.Fn realpath "const char *pathname" "char *resolved"
.Sh DESCRIPTION
The
.Fn realpath
function resolves all symbolic links, extra
.Dq /
characters and references to
.Pa /./
and
.Pa /../
in
.Fa pathname ,
and copies the resulting absolute pathname into the memory referenced by
.Fa resolved .
The
.Fa resolved
argument
.Em must
refer to a buffer capable of storing at least
.Dv PATH_MAX
characters, or be
.Dv NULL .
.Pp
The
.Fn realpath
function will resolve both absolute and relative paths
and return the absolute pathname corresponding to
.Fa pathname .
All components of
.Fa pathname
must exist when
.Fn realpath
is called.
.Sh RETURN VALUES
The
.Fn realpath
function returns
.Fa resolved
on success.
If
.Fa resolved
is
.Dv NULL
and no error occurred, then
.Fn realpath
returns a NUL-terminated string in a newly allocated buffer.
If an error occurs,
.Fn realpath
returns
.Dv NULL
and the contents of
.Fa resolved
are undefined.
.Sh ERRORS
The function
.Fn realpath
will fail if:
.Bl -tag -width Er
.It Bq Er EACCES
Read or search permission was denied for a component of
.Ar pathname .
.It Bq Er EINVAL
The
.Ar pathname
argument is a null pointer.
.It Bq Er EIO
An error occurred while reading from the file system.
.It Bq Er ELOOP
Too many symbolic links were encountered in translating
.Ar pathname .
.It Bq Er ENAMETOOLONG
A component of
.Ar pathname
exceeded
.Dv NAME_MAX
characters, or the entire
.Ar pathname
(including the terminating NUL) exceeded
.Dv PATH_MAX .
.It Bq Er ENAMETOOLONG
Pathname resolution of a symbolic link produced an intermediate
result whose length exceeds
.Dv PATH_MAX .
.It Bq Er ENOENT
A component of
.Ar pathname
does not name an existing file or
.Ar pathname
points to an empty string.
.It Bq Er ENOTDIR
A component of the path prefix is not a directory.
.It Bq Er ENOMEM
Sufficient storage space is unavailable for allocation.
.El
.Sh SEE ALSO
.Xr readlink 1 ,
.Xr realpath 1 ,
.Xr getcwd 3
.Sh STANDARDS
The
.Fn realpath
function conforms to
.St -p1003.1-2008 .
.Sh HISTORY
The
.Fn realpath
function call first appeared in
.Bx 4.4 .
.Pp
In
.Ox 6.6 ,
it was reimplemented on top of the
.Fn __realpath
system call.
Its calling convention differs from the standard
function by requiring
.Ar resolved
to not be
.Dv NULL
and by returning an integer,
zero on success, and -1 with corresponding errno on failure.
This is visible in the output of
.Xr kdump 1 .