readlink(3p)

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 nonnull 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 .

IEEE/The Open Group 2003 READLINK(P)