Learning Perl, 5th Edition

The stat and lstat Functions

While these file tests are fine for testing various attributes regarding a particular file or filehandle, they don’t tell the whole story. For example, there’s no file test that returns the number of links to a file or the owner’s user ID (uid). To get at the remaining information about a file, merely call the stat function, which returns pretty much everything that the stat Unix system call returns (hopefully more than you want to know).^[*] The operand to stat is a filehandle (including the _ virtual filehandle), or an expression that evaluates to a filename. The return value is either the empty list, indicating that the stat failed (usually because the file doesn’t exist), or a 13-element list of numbers, most easily described using the following list of scalar variables:

my($dev, $ino, $mode, $nlink, $uid, $gid, $rdev,
  $size, $atime, $mtime, $ctime, $blksize, $blocks)
    = stat($filename);

The names here refer to the parts of the stat structure, described in detail in the stat(2) manpage. You should probably look there for the detailed descriptions. But in short, here’s a quick summary of the important ones:

$dev and $ino

The device number and inode number of the file. Together they make up a “license plate” for the file. Even if it has more than one name (hard link), the combination of device and inode numbers should always be unique.

$mode

The set of permission bits for the file, and some other bits. If you’ve ever used the Unix command ls -l to get a detailed ...