There are many ways to read the last line of a file in perl, but as usual, not all are equal. 

#! perl -slw
use strict;
use Benchmark qw[ cmpthese ];
use Tie::File;
use File::ReadBackwards;

for our $file ( qw[ data/500k.dat data/1000k.dat data/2MB.dat ]) {
    print "\nComparing $file";
    cmpthese( -3, {
        'Tie::File' => q[
            my( @lines, $last );
            tie @lines, 'Tie::File', $file or die $!;
            $last = $lines[ -1 ];
            untie @lines;
#            print "TF:$last";
        ],
        'File::ReadBackwards' => q[
            my $last;

            tie *FILE, 'File::ReadBackwards', $file or die $!;
            $last = <FILE>;
            untie *FILE;
#            print "RB:$last";
        ],
        rawio => q[
            my( $last, $buffer );
            open FILE, '< :raw', $file or die $!;
            sysseek FILE, -1000, 2;
            sysread FILE, $buffer, 1000;
            $last = substr $buffer, 1+rindex( $buffer, "\n", length($b
+uffer)-2 );
            close FILE;
#            print "raw:$last";
        ],
        readfwd => q[
            my $last;
            open FILE, '<', $file or die $!;
            $last = <FILE> until eof FILE;
            close FILE;
#            print "RF:$last";
        ],
    });
}

__END__
P:\test>354830

Comparing data/500k.dat
                       Rate  Tie::File    readfwd File::ReadBackwards 
+     rawio
Tie::File            5.12/s         --       -94%                -99% 
+     -100%
readfwd              90.0/s      1657%         --                -88% 
+      -99%
File::ReadBackwards   775/s     15042%       762%                  -- 
+      -95%
rawio               14765/s    288372%     16314%               1805% 
+        --

Comparing data/1000k.dat
                       Rate  Tie::File    readfwd File::ReadBackwards 
+     rawio
Tie::File            2.51/s         --       -95%               -100% 
+     -100%
readfwd              45.9/s      1730%         --                -95% 
+     -100%
File::ReadBackwards   854/s     33931%      1759%                  -- 
+      -94%
rawio               15214/s    605971%     33011%               1681% 
+        --

Comparing data/2MB.dat
                       Rate  Tie::File    readfwd File::ReadBackwards 
+     rawio
Tie::File            1.25/s         --       -95%               -100% 
+     -100%
readfwd              22.9/s      1736%         --                -98% 
+     -100%
File::ReadBackwards  1040/s     83151%      4434%                  -- 
+      -93%
rawio               15087/s   1207959%     65694%               1351% 
+        --

[download]

Note: The figures are for 3 files (25 character lines), on one OS (Win32XP) and perl 5.8.3. YMMV.

Examine what is said, not who speaks.
"Efficiency is intelligent laziness." -David Dunham
"Think for yourself!" - Abigail

In reply to Reading from the end of a file. by BrowserUk

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