Hi there, Is it possible to write a regex to parse Access rules from a Cisco config file. Right now I have a working code, built on a bunch of nested if's to parse it. But it is only as elegant as a tumbleweed and I want to know whether it can be improved upon.

The basic format is as below (format specific to access rules in a ASA firewall)

access-list $acl_name extended $action $protocol $source_network $dest_network $ports .*

The challenging part is that some sections of the rule can have one, two or three words as below:

$protocols        -    (ip|tcp|udp) (1 word)
                    object-group <protocol object-group name> (2 word)

$source_network    -    host <host name> (2 words)
                    <ip address> <wildcard mask> (2 words)
                    object-group <network object-group name> (2 words)
                    any (1 word)

$dest_network    -    host <host name> (2 words)
                    <ip address> <wildcard mask> (2 words)
                    object-group <network object-group name> (2 words)
                    any (1 word)

$port            -    eq <port_no> (2 words)
                -    range <low_port> <high_port> (3 words)
                -    <blank> (0 word)

[download]

So, there are basically 2 x 2 x 2 x 3 = 24 possible formations. Can a regex with conditional matching and other advanced wizardry to tackle this particular case? I am not looking for 24 different patterns to match separately, it is only slightly better when compared to nested if code. Once I get a solution and hopefully understand it, I hope I can extended it to other form of ACLs (perhaps include Juniper devices also)

In reply to Regex to match a Cisco ACL by Anonymous Monk

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