More on Regular Expressions

If the regular expressions option was selected when creating a new template, or equivalently, if the line #conform use regular-expression is included at the top of a template, then regular expressions can be used when writing the compliance assessment rules. A typical rule that uses a regular-expression will use the “~=” wildcard operator as in the following example:

Some of the most basic and most commonly used regular expression syntax are as follows:

.	Any single character. Note that to match a period exactly, precede the dot with a backslash, “\.”
*	Zero or more instances of the previous character
+	One or more of the previous character
?	Zero or one of the previous character
[ ]	Any character from the set. [ch]at matches “cat” or “hat”
[^]	Any character not in the set.
( )	Groups patterns. (cat\|hat) matches “cat” or “hat”
[a-zA-Z]	Any character from a through z or A through Z, inclusive
[0-9]	Any integer from 0 through 9, inclusive
\	Used in front of a reserved regular expression character (such as “.” or “+”), to match that particular character. For example, to match “tacacs+” exactly, “tacacs\+” is required, as the plus sign has a special meaning in regular expression syntax.

Because some users may accidentally confuse wildcards with regular expressions, the Compliance Assessment Tool automatically converts some statements, as shown in the following examples:

“ATM*” is automatically converted to “ATM.*” - “ATM*” also matches “AT”, which is in most cases unintended by the user.
“*ATM” is automatically converted to “.*ATM” - “*ATM” is actually illegal regular expression syntax.

Note:

When used in regular expressions, blank spaces are respected. They are not ignored.

Some examples are shown below:

ip address.*	To match the ip address.
description.*	To match the description.
tacacs\+	To match “tacacs+” exactly, instead of just “tacacs”
version 12\..*	To ensure the version begins with “12.”
net .*00	To ensure the net id ends with two zeros
router eigrp (100\|299)	To match “router eigrp 100” or “router eigrp 299”
tacacs-server host 192\.122\.[0-9]+\.[0-9]+	To ensure the IP address is declared 192.122.x.y where x and y are integers.