stat

Here's what the UNIX man page on stat has to say about the difference
between a file change and  a file modification:

st_mtime  Time when data was last modified.  Changed by  the following 
functions:   creat(),  mknod(), pipe(), utime(), and write(2).

st_ctime  Time when file status was last  changed.   Changed by  the 
following  functions: chmod(), chown(), creat(), link(2), mknod(), pipe(),
unlink(2), utime(), and write().

So a modification is a change in the data, whereas a change also happens if
you modify file permissions and so on.

Note that in the docs above, the array is zero based. I scratched my head a
couple of times, before decreasing each item by one. ie - stat for file
size is actually 7 !

When you get a time from stat, like the date modified, you'll get a
timestamp returned.  You can use date() to convert it into a human readable
format:

$modified = stat("yourfile.html"); 
echo date("l, F dS",$modified[9]);

This function returns NULL if an invalid filename is entered.  This
function also does not work on remote files.

Remember that arrays are numbered from 0, whereas this document page is
numbered from 1.

$s = stat($file); 
$bytes = $s[7];

*not* $s[8], as you might think from quickly glancing at the list of
elements that stat() returns.

I think "3. inode protection mode" is incorrect.  Value 2 in the
array actually seems to actually correspond to st_mode from a C stat()
call, ie what the UNIX man pages call file "mode", or what I
would call "file type".

At the moment, I'm trying to reliably detect files that are not regular
files or directories.  I don't seem to be able to do this with is_file and
is_dir (this seems to mess up on special files, eg named pipes).

What I have constructed below seems to do what I want, but careful if you
want to reuse it: it isn't well tested yet and the constant values are from
a system file on Solaris 8.

// from /usr/include/sys/stat.h -- careful: probably only valid on Solaris
define("S_IFMT",  0xF000);
define("S_IFREG", 0x8000);
define("S_IFDIR", 0x4000);

if ((s = lstat($fileName)) == false)
die("ERROR: failed to stat file $fileName");

$type = s[2] & S_IFMT;
if (($type != S_IFREG) && ($type != S_IFDIR))
die("ERROR: expecting file or directory and found something else at
$fileName");

If you'd like to get information about a symlink, rather than the file it's
pointing to, use the lstat() function instead.  Took me a little while to
figure that out...

it's probably more readable to just use the associative key instead of the
numeric index. it'll also save you some head-scratching. for instance:

$info = stat('path/file');
echo $info[4];
echo $info['uid'];

will both output the same thing. using the print_r() function is really
pretty awesome for error-testing arrays just like this one. just be sure to
surround it in <PRE> tags if you are sending output to a browser.