Learning Perl, Fourth Edition

The stat and lstat Functions

Though 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, call the stat function, which returns pretty much everything that the stat Unix system call returns (and more than you want to know).^[270] The operand to stat is a 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 look there for the detailed descriptions. 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 will 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 (long) file listing, you’ll see that each line of output starts with ...