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    copied!<p>There is a library for Ruby called <a href="https://github.com/flori/file-tail" rel="nofollow noreferrer">File::Tail</a>. This can get you the last N lines of a file just like the UNIX tail utility.</p> <p>I assume there is some seek optimization in place in the UNIX version of tail with benchmarks like these (tested on a text file just over 11M):</p> <pre><code>[john@awesome]$du -sh 11M.txt 11M 11M.txt [john@awesome]$time tail -n 25 11M.txt /sbin/ypbind /sbin/arptables /sbin/arptables-save /sbin/change_console /sbin/mount.vmhgfs /misc /csait /csait/course /.autofsck /~ /usb /cdrom /homebk /staff /staff/faculty /staff/faculty/darlinr /staff/csadm /staff/csadm/service_monitor.sh /staff/csadm/.bash_history /staff/csadm/mysql5 /staff/csadm/mysql5/MySQL-server-community-5.0.45-0.rhel5.i386.rpm /staff/csadm/glibc-common-2.3.4-2.39.i386.rpm /staff/csadm/glibc-2.3.4-2.39.i386.rpm /staff/csadm/csunixdb.tgz /staff/csadm/glibc-headers-2.3.4-2.39.i386.rpm real 0m0.012s user 0m0.000s sys 0m0.010s </code></pre> <p>I can only imagine the Ruby library uses a similar method.</p> <p><strong>Edit:</strong></p> <p>for Pax's curiosity:</p> <pre><code>[john@awesome]$time cat 11M.txt | tail -n 25 /sbin/ypbind /sbin/arptables /sbin/arptables-save /sbin/change_console /sbin/mount.vmhgfs /misc /csait /csait/course /.autofsck /~ /usb /cdrom /homebk /staff /staff/faculty /staff/faculty/darlinr /staff/csadm /staff/csadm/service_monitor.sh /staff/csadm/.bash_history /staff/csadm/mysql5 /staff/csadm/mysql5/MySQL-server-community-5.0.45-0.rhel5.i386.rpm /staff/csadm/glibc-common-2.3.4-2.39.i386.rpm /staff/csadm/glibc-2.3.4-2.39.i386.rpm /staff/csadm/csunixdb.tgz /staff/csadm/glibc-headers-2.3.4-2.39.i386.rpm real 0m0.350s user 0m0.000s sys 0m0.130s </code></pre> <p>still under a second, but if there is a lot of file operations this makes a big difference.</p>
 

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