[Pdx-pm] traversing (and accessing values in) a hash of hashes

James marks jamarks at jamarks.com
Sat Dec 11 17:55:41 CST 2004

Hello folks,

I've been to a Portland Perl Mongers meeting only once so I'm sure you 
don't remember me but I'm wondering if any of you could help me with a 
code problem? I'm relatively new to Perl, coming to it from 
AppleScript, and I've written a Perl script that parses my server 
access_log and creates a hash of hashes that looks essentially like 
this: =
				$user_agent = "...GoogleBot..."
				$user_type  = "robot" =
				$user_agent = "...Linux...Firefox..."
				$user_type  = "human" =
				$user_agent = "...Yahoo! Slurp..."
				$user_type  = "robot" =
				$user_agent = "...Windows...MSIE..."
				$user_type  = "human"

So, in the first hash, the ip address is the key and the value is the 
second, nested hash.

I want to traverse that hash of hashes to extract the user agent of 
each IP whose user type is "robot" like this:

LIST OF ROBOTS VISITING SITE: "...GoogleBot..." "...Yahoo! Slurp..."

I've been struggling with various versions of a foreach loop but can't 
seem to get it to work. Is it possible to traverse a hash of hashes and 
extract data based on a value from a key/value pair that is nested in 
another hash?

I could just create two hashes, one for humans and one for robots, but 
one hash that contains all the information seemed to be a more elegant 

Any help would be greatly appreciated.


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