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READLINK(2) System Calls Manual READLINK(2)

readlink, readlinkat — read value of a symbolic link

library “libc”

#include <unistd.h>

ssize_t
readlink(const char * restrict path, char * restrict buf, size_t bufsiz);

ssize_t
readlinkat(int fd, const char * restrict path, char * restrict buf, size_t bufsiz);

() places the contents of the symbolic link path in the buffer buf, which has size bufsiz. readlink() does not append a NUL character to buf.

() works the same way as readlink() except if path is relative. In that case, it is looked up from a directory whose file descriptor was passed as fd. Search permission is required on this directory. fd can be set to AT_FDCWD in order to specify the current directory.

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 errno.

A typical use is illustrated in the following piece of code which reads the contents of a symbolic link named /symbolic/link and stores them as null-terminated string:

#include <limits.h>
#include <unistd.h>

char buf[PATH_MAX];
ssize_t len;

if ((len = readlink("/symbolic/link", buf, sizeof(buf)-1)) == -1)
	error handling;
buf[len] = '\0';

readlink() and readlinkat() will fail if:

[]
Search permission is denied for a component of the path prefix.
[]
buf extends outside the process's allocated address space.
[]
The named file is not a symbolic link.
[]
An I/O error occurred while reading from the file system.
[]
Too many symbolic links were encountered in translating the pathname.
[]
A component of a pathname exceeded {NAME_MAX} characters, or an entire path name exceeded {PATH_MAX} characters.
[]
The named file does not exist.
[]
A component of the path prefix is not a directory.

In addition, readlinkat() will fail if:

[]
path does not specify an absolute path and fd is neither AT_FDCWD nor a valid file descriptor open for reading or searching.
[]
path is not an absolute path and fd is a file descriptor associated with a non-directory file.

lstat(2), stat(2), symlink(2), symlink(7)

The readlink() function conforms to IEEE Std 1003.1-2001 (“POSIX.1”). readlinkat() conforms to IEEE Std 1003.1-2008 (“POSIX.1”).

The readlink() function appeared in 4.2BSD. The type returned was changed from int to ssize_t in NetBSD 2.1.

July 28, 2013 NetBSD-9.2