Getting Information About a File With stat

Getting Information About a File With stat

The stat function produces useful information about files that you can use in your file management functions. The stat function returns a thirteen-element array of file information using the syntax:

open ([FILE_HANDLE_NAME], "[filename]")|| 
     &CgiDie ("Can't open file");
     ($dev, $ino, $mode, $nlink, $uid, $gid, $rdev, $size,   
            $atime, $mtime, $ctime, $blksize, $blocks) =   
            stat([FILE_HANDLE_NAME]);
     close ([FILE_HANDLE_NAME]);

The following table describes the elements returned by stat

Variable	Description
$dev	The device that the file resides on
$ino	The inode for this file
$mode	The permissions for the file
$nlink	The number of hard links to the file
$uid	The numerical user ID for the file owner
$gid	The numerical group ID for the file owner
$rdev	The device type if the file is a device
$size	The size of the file in bytes
$atime	When the file was last accessed
$mtime	When the file was last modified
$ctime	When the file status was last changed
$blksize	The optimal block size for i/o operations on the file system containing the file
$blocks	The number of blocks allocated to the file

For the most part, CGI scripts will need to take advantage only of $atime, $mtime, $ctime, $mode and $size. $size and $mode are fairly straight forward in usage. However, the usage of the "time" variables is a bit subtle.
The time values returned by stat are formatted in terms of the number of non-leap seconds since January 1, 1970, UTC. Thus, the stat function might yield a result such as $mtime is equal to "838128443". Likewise, the time function returns the current time in the same format. Thus, the scalar variable $current_time is assigned the current time with the following syntax:

$current_time = time;

Once you have both the age of the file and the current time, you can use arithmetic to compare them for various operations such as the pruning of a Session Files directory after a certain amount of time.
For example, the following code snippet can be used to prune the file "289576893.dat" if it is older than an administratively-defined amount of time.

$seconds_to_save = 3600;
$age_of_file = $current_time - $mtime ;
if ($age_of_file > $seconds_to_save)
   {
   unlink ("289576893.dat");
   }

If you are interested in what the actual day is, and not the number of seconds since 1970, you must use the localtime function to convert the value to a more human-recognizable form using the syntax:

($sec, $min, $hour, $mday, $mon, $year, $wday, $yday, $isdst) = localtime (time);

The following code gets the same information for an $mtime value extracted from stat:

($sec, $min, $hour, $mday, $mon, $year,
$wday, $yday, $isdst) = localtime ($mtime);

Additional Resources:

File Tests
Table of Contents
Opening, Reading and Closing Directories

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