This also removes the last line with SIL. This is not how i wanted

ReadBackwards() has to do strange things with tell, so a little extra work is involved. Try this version:

#! perl -slw
use strict;
use File::ReadBackwards;

my $file = $ARGV[ 0 ];

tie *BW, 'File::ReadBackwards', $file;

my $lastpos = -s( $file );
my $len = 0;
while( <BW> ) {
    $len = length() +1;
    next unless length >1;
    last unless /SIL/;
    $lastpos = tell( BW );
}
truncate $file, $lastpos + $len;
close BW;
[download]

Note: You won't need the +1 in the  $len = length() +1; line if you are not on Windows.