yes yes, ive read the faq, camel, cookbook and searched deja, but am still
not sure on the best way to do this.

What is the most efficient & fastest way of reading the last line of a flat
file (small or large)?

Ive heard these solutions:
1) Read the whole file into an array, then process. (how well would this
work for large files???)
2) Open the file, seek to the end, seek back a little, use sysread to read
the part you seeked back over. If it contains a newline, you now know the
part you can read, else you seek back a bit more, rinse and repeat.
3) using tell() and truncate():
        open (FH, "+< $file");
        while ( <FH> ) { $addr = tell(FH) unless eof(FH) }
        truncate(FH, $addr);
This deletes the last line of a file without making a copy or reading the
whole file into memory, but how can it be used to return the last line?
(then i guess you could process it then append it back on - quick?)
4) is there a tail function for perl? as in unix? where the end is read
only? (perhaps I could then tell/truncate??)

I want to try and avoid reading the whole file just to find the end, as
presumably this could take ages with a large file.

Any opinons on this??

# perldoc -q tail
=head1 Found in /opt/perl5.00503/lib/5.00503/pod/perlfaq5.pod

=head2 How do I do a C<tail -f> in perl?

As far as 'which of the methods is best?' goes. Probably depends. I
would just code for the general case, which disallows slurping in the
whole file (what if it's 3 GB large?).

The Perl Power Tools also come with a tail. Have a look at that.
http://language.perl.com/

I recommend running your own tests.  It's good to
profit from the experience of others.  However, cod-
ing each of the possibilities you're already
mentioned is so quick in Perl that, if the differ-
ences in performance truly matter to you, your time
will be will spent on measuring their performance
yourself.

Please do consider the `tail -1 ...` alternative.
I suspect that Mr. Verbruggen's reservations about
it might not apply in your situation.
--

Try this at a command prompt:

perldoc -q tail

[snip of code showing this]

Actually, I find that ActiveState Perl on win32 and the Perl Power Tools
can make working on win32 platforms much nicer.  There's a tail program
in there, IIRC...

And in considerably less lines:

Abigail
--

             "\150\145\162\040\120\145\162\154\040\110\141\143\153\145\162".

So here is a burning question on reading the last line of a file that
has been bugging me for months....

This WILL work

open(FILE, '/dir/file.file') or die "Can't read file.file, $!\n";
 $line = (<FILE>)[-1];
close FILE  or warn "Can't close file.file, $!\n";

print "$line\n";

# prints last line or (<FILE>)[5] prints... well, you know..

BUT!

Is the whole file being read into memory so it can be treated as an
array, or is Perl counting $/ and then pulling the proper line or???

I haven't found any docs that tell me what's going on here.  I may be
looking in the wrong places of course.

Interestingly, this code will ONLY grab one line from the file, attempts
to run a loop and get more than one line seem doomed to failure.

Something like:

open(FILE, '/dir/file.file') or die "Can't read file.file, $!\n";

close FILE  or warn "Can't close file.file, $!\n";

or

open(FILE, '/dir/file.file') or die "Can't read file.file, $!\n";
$string .= (<FILE>)[1],"\n";
$string .= (<FILE>)[2],"\n";
close FILE  or warn "Can't close file.file, $!\n";

will ONLY grab the first element, subsequent arguments are ignored.  
'Course I could be doing something wrong. :-)

I've used this once or twice on small files on (shudder) win32 where I
didn't have tail handy and I needed a specific line, but have always
been hesitant to use it on bigger files. And a bit hesitant to use it in
production code since I don't really understand exactly what's going on.

Interested in comments.

But:

my $line;
$line = $_ while(<FILE>);

only reads in one line at a time.  Of course, it still does an
assignment for each line in the file, and it has to scan the whole
file.

Something like this avoids the assignments:

while(<FILE>) {
        next unless eof FILE;
        $line = $_;

Probably it depends on the size of the file you want to open what's
most efficient (a seek to the end and jumping backwards, slurping in
the file, scanning each line until the last).

You could have a look to see how this is implemented in the tail that comes
with the Perl Power Tools: http://language.perl.com/ppt. (It seems
that  that tail always scans the file if it's text, so maybe it was
judged to be the best general case).

Martien