Another hint is use the following, which I think is more readable :-)

my $dn = 'corpid=xxxxxx,ou=people,o=corp';
my ($ou) = $dn =~ /ou=(.*?),/;
print "ou = $ou\n";
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From perldoc perlre:

       Sometimes minimal matching can help a lot.  Imagine you’d like 
+to match
       everything between "foo" and "bar".  Initially, you write somet
+hing
       like this:

           $_ =  "The food is under the bar in the barn.";
           if ( /foo(.*)bar/ ) {
               print "got <$1>\n";
           }

       Which perhaps unexpectedly yields:

         got <d is under the bar in the >

       That’s because ".*" was greedy, so you get everything between t
+he first
       "foo" and the last "bar".  Here it’s more effective to use mini
+mal
       matching to make sure you get the text between a "foo" and the 
+first
       "bar" thereafter.

           if ( /foo(.*?)bar/ ) { print "got <$1>\n" }
         got <d is under the >
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