map a null/missing variable?

Ruslan Ermilov ru at
Thu Mar 14 05:13:17 UTC 2013

On Wed, Mar 13, 2013 at 02:19:50PM -0400, AJ Weber wrote:
> OK,
> So I'm still working on my caching "issue", but this is a more general 
> question, so for the sake of indexing and helping others in the future 
> with (hopefully) a response...
> How do I use a map to map the lack of a variable/header/cookie (NULL?) 
> to a value?  I can't use "default", because when there IS a value it 
> will be a random set of characters.

You can't handle the lack of a variable (it'll cause a syntax
error in configuration).  Mapping of an unset variable is easy:

map $http_foo $my_var {
    ""      unset;
    default set;

> So that said, if a regex like ".+" would work for "any value" and I use 
> 'default' for the NULL, I would try that. :)

That's suboptimal.

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