IO::Seekable
See the current Perl documentation for IO::Seekable.
Here is our local, out-dated (pre-5.6) version:

IO::Seekable - supply seek based methods for I/O objects

use IO::Seekable; package IO::Something; @ISA = qw(IO::Seekable);

IO::Seekable
does not have a constuctor of its own as is intended to be inherited by
other IO::Handle
based objects. It provides methods which allow seeking of the file
descriptors.
If the
C functions
fgetpos()
and
fsetpos()
are available, then
IO::File::getpos
returns an opaque value that represents the current position of the
IO::File, and IO::File::setpos
uses that value to return to a previously visited position.
See perlfunc for complete descriptions of each of the following supported IO::Seekable
methods, which are just front ends for the corresponding built-in
functions:
seek tell
SEE ALSO
HISTORY
Derived from FileHandle.pm by Graham Barr <bodg@tiuk.ti.com>