Rewrite path only if file/folder does not exist

I am using the IIS Rewriter module wi开发者_如何学Pythonth my web.config, and would like to redirect certain requests for content in a subdirectory only if there isn't an actual folder/file that already matches the request. How can I do this?

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A little late but I'm going to leave an answer here for the next person that find this post.

Basically you need to add a couple of conditions to the rewrite rule. Example:

<rule name="Remove trailing slash" stopProcessing="true">
    <match url="(.*)/$"/>
    <conditions>
        <add input="{REQUEST_FILENAME}" matchType="IsFile" negate="true"/>
        <add input="{REQUEST_FILENAME}" matchType="IsDirectory" negate="true"/>
    </conditions>
    <action type="Redirect" redirectType="Permanent" url="{R:1}" appendQueryString="true"/>
</rule>