title: How can I view log files in Linux and apply custom filters while viewing?
body: <p>I need to read through some gigantic log files on a Linux system.  There's a lot of clutter in the logs.  At the moment I'm doing something like this:</p>
  
  <pre><code>cat logfile.txt | grep -v "IgnoreThis\|IgnoreThat" | less
  </code></pre>
  
  <p>But it's cumbersome -- every time I want to add another filter, I need to quit <code>less</code> and edit the command line.  Some of the filters are relatively complicated and may be multi-line.</p>
  
  <p>I'd like some way to apply filters as I am reading through the log, and a way to save these filters somewhere.</p>
  
  <p>Is there a tool that can do this for me?  I can't install new software so hopefully it's something that would already be installed -- e.g., less, vi, something in a Python or Perl lib, etc.</p>
  
  <p>Changing the code that generates the log to generate less is not an option.</p>