#!/usr/bin/perl
use strict;
use Fcntl qw(SEEK_END SEEK_CUR);

my $f = shift;
open F, "+<", $f or die "Couldn't open $f: $!\n";

seek F, -1, SEEK_END;
seek F, -2, SEEK_CUR while (getc(F) eq "\n");

truncate F, tell F;