I'd say I agree with pretty much everything said so far. Here are a few of my own for interpreted languages, which I probably should write down somewhere:

• Don't call other turing complete languages when your shell can already do basic string manipulation.
  
• Use #!/usr/bin/env python, not #!/usr/bin/python.
  
• Don't include huge walls of text as comments, write proper documentation instead.
  
• Use the heredoc format, not dozens of echo or printf statements.