#!/usr/bin/perl -w

use strict;

my $file = shift or die;
open my $fh, "+<$file" or die "$!";

my $size = 4096;

my ($cur_pos, $buf);
seek $fh, -$size, 2;
while (1) {
    $cur_pos = tell $fh;
    read $fh, $buf, $size;
    last if $buf =~ m/\S/s;
    seek $fh, -$size, 1;
}

$buf =~ m/(\s+)$/s;
$cur_pos += $-[0];

truncate $fh, $cur_pos;

close $fh;

exit 0;