Can I create a conditional find and replace with a regular expression?

I am trying to use an NginX substitution filter that allows regular expressions. I can get it to work in a basic way, i.e. replace phone

with telephone

, but I cannot get it to conditionally replace a line of text.

Here is the XML validation for validation:

eat apples cantaloupe bananas often

      

        
        
        
      

    

I would like to implement the following set of rules:

• Look for a line starting with eat
  
  and ending withoften
  
  
• If string contains bananas
  
  , replace bananas
  
  withand especially bananas
  
  
• If the string does not contain bananas, do nothing with the string

I know I can use something like this to make parts of a string accessible:

/(eat.*)(bananas)?(.*often)/

      

        
        
        
      

    

I could use the following rule for replacement, assuming that is bananas

present:

   $1 and especially $2 $3

      

        
        
        
      

    

But this will give an odd result if bananas

not:

entrance

eat apples cantaloupe often

      

        
        
        
      

    

output:

eat apples cantaloupe and especially often

      

        
        
        
      

    

Do I need an external operator? I have read this article but I am still having problems.