access - determine accessibility of file
#define R_OK 4/* test for read permission */
#define W_OK 2/* test for write permission */
#define X_OK 1/* test for execute (search) permission */
#define F_OK 0/* test for presence of file */
accessible = access(path, mode)
Access checks the given file path for accessibility according to mode, which is an inclu-
sive or of the bits R_OK, W_OK and X_OK. Specifying mode as F_OK (i.e., 0) tests whether
the directories leading to the file can be searched and the file exists.
The real user ID and the group access list (including the real group ID) are used in veri-
fying permission, so this call is useful to set-UID programs.
Notice that only access bits are checked. A directory may be indicated as writable by
access, but an attempt to open it for writing will fail (although files may be created
there); a file may look executable, but execve will fail unless it is in proper format.
If path cannot be found or if any of the desired access modes would not be granted, then a
-1 value is returned; otherwise a 0 value is returned.
Access to the file is denied if one or more of the following are true:
[ENOTDIR] A component of the path prefix is not a directory.
[EINVAL] The pathname contains a character with the high-order bit set.
[ENAMETOOLONG] A component of a pathname exceeded 255 characters, or an entire path name
exceeded 1023 characters.
[ENOENT] The named file does not exist.
[EACCES] Search permission is denied for a component of the path prefix.
[ELOOP] Too many symbolic links were encountered in translating the pathname.
[EROFS] Write access is requested for a file on a read-only file system.
[ETXTBSY] Write access is requested for a pure procedure (shared text) file that is
[EACCES] Permission bits of the file mode do not permit the requested access, or
search permission is denied on a component of the path prefix. The owner
of a file has permission checked with respect to the ``owner'' read, write,
and execute mode bits, members of the file's group other than the owner
have permission checked with respect to the ``group'' mode bits, and all
others have permissions checked with respect to the ``other'' mode bits.
[EFAULT] Path points outside the process's allocated address space.
[EIO] An I/O error occurred while reading from or writing to the file system.
4th Berkeley Distribution May 22, 1986 ACCESS(2)