READLINK(P) POSIX Programmer's Manual READLINK(P)NAMEreadlink - 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 con‐
tents of the symbolic link as returned by readlink(), this proposal was
rejected, and the historical practice retained.
FUTURE DIRECTIONS
None.
SEE ALSOlstat() , 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 .
IEEE/The Open Group 2003 READLINK(P)
