PHP : Directories - [19.3] Getting File Information

19.3.1 Problem

You want to read a file's metadata; for example, permissions and ownership.

19.3.2 Solution

Use stat( ), which returns an array of information about a file:

$info = stat('harpo.php');

19.3.3 Discussion

The function stat( ) returns an array with both numeric and string indexes with information about a file. The elements of this array are in Table 19-3.

Table 19-3. Information returned by stat( )

Numeric index	String index	Value
0	dev	Device
1	ino	Inode
2	mode	Permissions
3	nlink	Link count
4	uid	Owner's user ID
5	gid	Group's group ID
6	rdev	Device type for inode devices (-1 on Windows)
7	size	Size (in bytes)
8	atime	Last access time (epoch timestamp)
9	mtime	Last change time of contents (epoch timestamp)
10	ctime	Last change time of contents or metadata (epoch timestamp)
11	blksize	Block size for I/O (-1 on Windows)
12	blocks	Number of block allocated to this file

The mode element of the returned array contains the permissions expressed as a base 10 integer. This is confusing since permissions are usually either expressed symbolically (e.g., ls's -rw-r--r-- output) or as an octal integer (e.g., 0644). To convert the permissions to a more understandable format, use base_convert( ) to change the permissions to octal:

$file_info = stat('/tmp/session.txt');
$permissions = base_convert($file_info['mode'],10,8);

This results in a six-digit octal number. For example, if ls displays the following about /tmp/session.txt:

-rw-rw-r--    1 sklar    sklar          12 Oct 23 17:55 /tmp/session.txt

Then $file_info['mode'] is 33204 and $permissions is 100664. The last three digits (664) are the user (read and write), group (read and write), and other (read) permissions for the file. The third digit, 0, means that the file is not setuid or setgid. The leftmost 10 means that the file is a regular file (and not a socket, symbolic link, or other special file).

Because stat( ) returns an array with both numeric and string indexes, using foreach to iterate through the returned array produces two copies of each value. Instead, use a for loop from element 0 to element 12 of the returned array.

Calling stat( ) on a symbolic link returns information about the file the symbolic link points to. To get information about the symbolic link itself, use lstat( ).

Similar to stat( ) is fstat( ), which takes a file handle (returned from fopen( ) or popen( )) as an argument. You can use fstat( ) only on local files, however, not URLs passed to fopen( ).

PHP's stat( ) function uses the underlying stat(2) system call, which is expensive. To minimize overhead, PHP caches the result of calling stat(2). So, if you call stat( ) on a file, change its permissions, and call stat( ) on the same file again, you get the same results. To force PHP to reload the file's metadata, call clearstatcache( ), which flushes PHP's cached information. PHP also uses this cache for the other functions that return file metadata: file_exists( ), fileatime( ), filectime( ), filegroup( ), fileinode( ), filemtime( ), fileowner( ), fileperms( ), filesize( ), filetype( ), fstat( ), is_dir( ), is_executable( ), is_file( ), is_link( ), is_readable( ), is_writable( ), and lstat( ).