xnu-7195.101.1.tar.gz

[apple/xnu.git] / bsd / man / man2 / readlink.2

.\"	$NetBSD: readlink.2,v 1.7 1995/02/27 12:35:54 cgd Exp $
.\"
.\" Copyright (c) 1983, 1991, 1993
.\"	The Regents of the University of California.  All rights reserved.
.\"
.\" 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. All advertising materials mentioning features or use of this software
.\"    must display the following acknowledgement:
.\"	This product includes software developed by the University of
.\"	California, Berkeley and its contributors.
.\" 4. 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.
.\"
.\"     @(#)readlink.2	8.1 (Berkeley) 6/4/93
.\"
.Dd June 4, 1993
.Dt READLINK 2
.Os BSD 4.2
.Sh NAME
.Nm readlink ,
.Nm readlinkat
.Nd read value of a symbolic link
.Sh SYNOPSIS
.Fd #include <unistd.h>
.Ft  ssize_t
.Fo readlink
.Fa "const char *restrict path"
.Fa "char *restrict buf"
.Fa "size_t bufsize"
.Fc
.Ft ssize_t
.Fo readlinkat
.Fa "int fd" "const char *restrict path" "char *restrict buf" "size_t bufsize"
.Fc
.Sh DESCRIPTION
.Fn readlink
places the contents of the symbolic link
.Fa path
in the buffer
.Fa buf ,
which has size
.Fa bufsize .
.Nm Readlink
does not append a
.Dv NUL
character to
.Fa buf .
.Pp
The
.Fn readlinkat
system call is equivalent to
.Fn readlink
except in the case where
.Fa path
specifies a relative path.
In this case the symbolic link whose content is read relative to the
directory associated with the file descriptor
.Fa fd
instead of the current working directory.
If
.Fn readlinkat
is passed the special value
.Dv AT_FDCWD
in the
.Fa fd
parameter, the current working directory is used and the behavior is
identical to a call to
.Fn readlink .
.Sh RETURN VALUES
The call returns the count of characters placed in the buffer
if it succeeds, or a -1 if an error occurs, placing the error
code in the global variable
.Va errno .
.Sh ERRORS
.Fn readlink
will fail if:
.Bl -tag -width Er
.\" ===========
.It Bq Er EACCES
Search permission is denied for a component of the path prefix.
.\" ===========
.It Bq Er EFAULT
.Fa Buf
extends outside the process's allocated address space.
.\" ===========
.It Bq Er EINVAL
The named file is not a symbolic link.
.\" ===========
.It Bq Er EIO
An I/O error occurred while reading from the file system.
.\" ===========
.It Bq Er ELOOP
Too many symbolic links are encountered in translating the pathname.
This is taken to be indicative of a looping symbolic link.
.\" ===========
.It Bq Er ENAMETOOLONG
A component of a pathname exceeded 
.Dv {NAME_MAX}
characters, or an entire path name
(possibly expanded by a symbolic link) exceeded 
.Dv {PATH_MAX}
characters.
.\" ===========
.It Bq Er ENOENT
The named file does not exist.
.\" ===========
.It Bq Er ENOTDIR
A component of the path prefix is not a directory.
.El
.Pp
In addition to the errors returned by the
.Fn readlink ,
the
.Fn readlinkat
may fail if:
.Bl -tag -width Er
.It Bq Er EBADF
The
.Fa path
argument does not specify an absolute path and the
.Fa fd
argument is neither
.Dv AT_FDCWD
nor a valid file descriptor open for searching.
.It Bq Er ENOTDIR
The
.Fa path
argument is not an absolute path and
.Fa fd
is neither
.Dv AT_FDCWD
nor a file descriptor associated with a directory.
.El
.Sh LEGACY SYNOPSIS
.Fd #include <unistd.h>
.Pp
.Ft int
.br
.Fo readlink
.Fa "const char *path"
.Fa "char *buf"
.Fa "int bufsize"
.Fc ;
.Pp
The function type and the type of
.Fa bufsize
have changed.
.Sh SEE ALSO
.Xr lstat 2 ,
.Xr stat 2 ,
.Xr symlink 2 ,
.Xr compat 5 ,
.Xr symlink 7
.Sh STANDARDS
The
.Fn readlinkat
system call is expected to conform to POSIX.1-2008 .
.Sh HISTORY
The
.Fn readlink
function call appeared in
.Bx 4.2 .
The
.Fn readlinkat
system call appeared in OS X 10.10