my $o_tail=File::Tail->new( 
    name               =>  $scan_log_file, 
    maxinterval        =>  1, 
    adjustafter        =>  1, 
    ignore_nonexistant =>  1, 
    reset_tail         => -1,
    tail               => -1,
);

while( my $line = $o_tail->read() )
{
    if( $line =~ m/finished/ )
    {
    	# Do stuff
    }
}