PHP Directories Getting File Information

PHP Directories

Getting File Information

Problem

You want to read a file’s metadata—for example, permissions and ownership.

Solution

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

       $info = stat('harpo.php');

Discussion

stat() returns an array with both numeric and string indexes with information about a file.

Table  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 blocks allocated to this file

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The mode element of the returned array contains the permissions expressed as a base 10 integer. This is confusing because 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 the more understandable octal format, use base_convert():

       $file_info = stat('/tmp/session.txt');

       $permissions = base_convert($file_info['mode'],10,8);

Here, $permissions is 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 filehandle (returned from fopen() or popen()) as an argument.

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().