```ruby
# Copyright (c) 2014, Stuart Glenn, OMRF
# Distributed under a BSD 3-Clause
# Full license available in LICENSE.txt distributed with this software

class Optical::Filters::NullFilter
  def initialize(lib,name,conf)
    @lib = lib
    @name = name
    @conf = conf
  end

  def filter_to(output_bam)
    @lib.filtered_path = @lib.aligned_path
    return true
  end

  def filter_through_awk_script(script,output_bam,min_score=0)
    File.delete(output_bam)
    cmd = @conf.cluster_cmd_prefix(free:1, max:12, sync:true, name:"filt_#{@name}") +
      %W(/bin/bash -o pipefail -o errexit -c)

    filt_cmd = "samtools view -h -q #{min_score} #{@lib.aligned_path} |" +
      "awk -f #{script} | samtools view -Sbh - > #{output_bam}"
    cmd << "\"#{filt_cmd}\""
    puts cmd.join(" ") if @conf.verbose
    unless system(*cmd)
      return false
    end
    @lib.filtered_path = output_bam
    return true
  end
end
```

Fix delete when something is not yet there
user
```ruby
# Copyright (c) 2014, Stuart Glenn, OMRF
# Distributed under a BSD 3-Clause
# Full license available in LICENSE.txt distributed with this software

class Optical::Filters::NullFilter
  def initialize(lib,name,conf)
    @lib = lib
    @name = name
    @conf = conf
  end

  def filter_to(output_bam)
    @lib.filtered_path = @lib.aligned_path
    return true
  end

  def filter_through_awk_script(script,output_bam,min_score=0)
    File.delete(output_bam) if File.exists?(output_bam)
    cmd = @conf.cluster_cmd_prefix(free:1, max:12, sync:true, name:"filt_#{@name}") +
      %W(/bin/bash -o pipefail -o errexit -c)

    filt_cmd = "samtools view -h -q #{min_score} #{@lib.aligned_path} |" +
      "awk -f #{script} | samtools view -Sbh - > #{output_bam}"
    cmd << "\"#{filt_cmd}\""
    puts cmd.join(" ") if @conf.verbose
    unless system(*cmd)
      return false
    end
    @lib.filtered_path = output_bam
    return true
  end
end
```
assistant