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READLINK
Section: POSIX Programmer's Manual (3P)
Updated: 2003
Index
Return to Main Contents
PROLOG
This manual page is part of the POSIX Programmer's Manual.
The Linux implementation of this interface may differ (consult
the corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
NAME
readlink - read the contents of a symbolic link
SYNOPSIS
#include <unistd.h>
ssize_t readlink(const char *restrict path, char *restrict
buf,
size_t bufsize);
DESCRIPTION
The readlink() function shall place the contents of the symbolic
link referred to by path in the buffer buf
which has size bufsize. If the number of bytes in the symbolic
link is less than bufsize, the contents of the
remainder of buf are unspecified. If the buf argument
is not large enough to contain the link content, the first
bufsize bytes shall be placed in buf.
If the value of bufsize is greater than {SSIZE_MAX}, the result
is implementation-defined.
RETURN VALUE
Upon successful completion, readlink() shall return the count
of bytes placed in the buffer. Otherwise, it shall return a
value of -1, leave the buffer unchanged, and set errno to indicate
the error.
ERRORS
The readlink() function shall fail if:
- EACCES
-
Search permission is denied for a component of the path prefix of
path.
- EINVAL
-
The path argument names a file that is not a symbolic link.
- EIO
-
An I/O error occurred while reading from the file system.
- ELOOP
-
A loop exists in symbolic links encountered during resolution of the
path argument.
- ENAMETOOLONG
-
The length of the path argument exceeds {PATH_MAX} or a pathname
component is longer than {NAME_MAX}.
- ENOENT
-
A component of path does not name an existing file or path
is an empty string.
- ENOTDIR
-
A component of the path prefix is not a directory.
The readlink() function may fail if:
- EACCES
-
Read permission is denied for the directory.
- ELOOP
-
More than {SYMLOOP_MAX} symbolic links were encountered during resolution
of the path argument.
- ENAMETOOLONG
-
As a result of encountering a symbolic link in resolution of the path
argument, the length of the substituted pathname
string exceeded {PATH_MAX}.
The following sections are informative.
EXAMPLES
Reading the Name of a Symbolic Link
The following example shows how to read the name of a symbolic link
named /modules/pass1.
-
#include <unistd.h>
char buf[1024];
ssizet_t len;
...
if ((len = readlink("/modules/pass1", buf, sizeof(buf)-1)) != -1)
buf[len] = '\0';
APPLICATION USAGE
Conforming applications should not assume that the returned contents
of the symbolic link are null-terminated.
RATIONALE
Since IEEE Std 1003.1-2001 does not require any association of file
times with symbolic links, there is no requirement
that file times be updated by readlink(). The type associated
with bufsiz is a size_t in order to be
consistent with both the ISO C standard and the definition of read().
The behavior
specified for readlink() when bufsiz is zero represents
historical practice. For this case, the standard developers
considered a change whereby readlink() would return the number
of non-null bytes contained in the symbolic link with the
buffer buf remaining unchanged; however, since the stat
structure member st_size value can be used to
determine the size of buffer necessary to contain the contents of
the symbolic link as returned by readlink(), this proposal
was rejected, and the historical practice retained.
FUTURE DIRECTIONS
None.
SEE ALSO
lstat(), stat(), symlink(),
the Base Definitions volume of IEEE Std 1003.1-2001, <unistd.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group. In the
event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online at
http://www.opengroup.org/unix/online.html .
Index
- PROLOG
-
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- RETURN VALUE
-
- ERRORS
-
- EXAMPLES
-
- Reading the Name of a Symbolic Link
-
- APPLICATION USAGE
-
- RATIONALE
-
- FUTURE DIRECTIONS
-
- SEE ALSO
-
- COPYRIGHT
-
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