minix/lib/libc/sys/readlink.2

.\"	$NetBSD: readlink.2,v 1.32 2013/07/29 11:49:31 wiz Exp $
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.\"     @(#)readlink.2	8.1 (Berkeley) 6/4/93
.\"
.Dd July 28, 2013
.Dt READLINK 2
.Os
.Sh NAME
.Nm readlink ,
.Nm readlinkat
.Nd read value of a symbolic link
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In unistd.h
.Ft ssize_t
.Fn readlink "const char * restrict path" "char * restrict buf" "size_t bufsiz"
.Ft ssize_t
.Fn readlinkat "int fd" "const char * restrict path" "char * restrict buf"\
 "size_t bufsiz"
.Sh DESCRIPTION
.Fn readlink
places the contents of the symbolic link
.Fa path
in the buffer
.Fa buf ,
which has size
.Fa bufsiz .
.Fn readlink
does not append a
.Dv NUL
character to
.Fa buf .
.Pp
.Fn readlinkat
works the same way as
.Fn readlink
except if
.Fa path
is relative.
In that case, it is looked up from a directory whose file
descriptor was passed as
.Fa fd .
Search permission is required on this directory.
.\"    (These alternatives await a decision about the semantics of O_SEARCH)
.\" Search permission is required on this directory
.\" except if
.\" .Fa fd
.\" was opened with the
.\" .Dv O_SEARCH
.\" flag.
.\"    - or -
.\" This file descriptor must have been opened with the
.\" .Dv O_SEARCH
.\" flag.
.Fa fd
can be set to
.Dv AT_FDCWD
in order to specify the current directory.
.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 EXAMPLES
A typical use is illustrated in the following piece of code
which reads the contents of a symbolic link named
.Pa /symbolic/link
and stores them as null-terminated string:
.Bd -literal -offset indent
#include \*[Lt]limits.h\*[Gt]
#include \*[Lt]unistd.h\*[Gt]

char buf[PATH_MAX];
ssize_t len;

if ((len = readlink("/symbolic/link", buf, sizeof(buf)-1)) == -1)
	error handling;
buf[len] = '\e0';
.Ed
.Sh ERRORS
.Fn readlink
and
.Fn readlinkat
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 were encountered in translating the pathname.
.It Bq Er ENAMETOOLONG
A component of a pathname exceeded
.Brq Dv NAME_MAX
characters, or an entire path name exceeded
.Brq 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,
.Fn readlinkat
will fail if:
.Bl -tag -width Er
.It Bq Er EBADF
.Fa path
does not specify an absolute path and
.Fa fd
is neither
.Dv AT_FDCWD
nor a valid file descriptor open for reading or searching.
.It Bq Er ENOTDIR
.Fa path
is not an absolute path and
.Fa fd
is a file descriptor associated with a non-directory file.
.El
.Sh SEE ALSO
.Xr lstat 2 ,
.Xr stat 2 ,
.Xr symlink 2 ,
.Xr symlink 7
.Sh STANDARDS
The
.Fn readlink
function conforms to
.St -p1003.1-2001 .
.Fn readlinkat
conforms to
.St -p1003.1-2008 .
.Sh HISTORY
The
.Fn readlink
function appeared in
.Bx 4.2 .
The type returned was changed from
.Ft int
to
.Ft ssize_t
in
.Nx 2.1 .