#! perl -sw
use strict;

open I, '<', $ARGV[0] or die $!;
seek I, 0, 2;
my $n = int( tell( I ) / 4 );
seek I, 0, 0;

my $s = $n;
for my $i ( 1 .. 4 ) {
    open O, '>', "split$i" or die $!;
    while( tell( I ) < $s ) {
        print O scalar <I>;
    }
    $s += $n;
    close O;
}
__END__
C:\test>dir words.txt
17/07/2011  15:52         1,941,858 words.txt

C:\test>split4 words.txt

C:\test>dir split*
08/02/2013  00:41           485,470 split1
08/02/2013  00:41           485,458 split2
08/02/2013  00:41           485,468 split3
08/02/2013  00:41           485,462 split4
08/02/2013  00:38               298 split4.pl