Something like (untested):

my $pat = qr {
   (?(DEFINE)
       (?<action>   (?:\s*\b(?:permit|deny)\b))
       (?<protocol> (?:\s*\b(?:tcp|upd|ip|object-group(?&object_group_
+name)\b))
       (?<object_group_name> (?:please define))
       (?<source>)  (?:\s*\b(?:object-group (?&object_group_name)|host
+ (?&host_address)|(?&network_address) (?&net_mask))\b))
       (?<host_address> (?:please define))
       (?<network_address> (?:please define))
       (?<net_mask> (?:please define))
       (?<destination>) (?&source))
       (?<port> (?:\s*\b(?:port (?&port_number)|range (?&low_port) (?&
+high_port)|)\b))
       (?<port_number> (?:please define))
       (?<low_port> (?:please define))
       (?<high_port> (?:please define))
)
acl ((?&action)) ((?&protocol)) ((?&source)) ((?&destination)) ((?&por
+t))
}x
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