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Using Metacharacters as Literal Tokens

You can remove the special meaning of a metacharacter by preceding it with a backslash (\). Such a construction denotes that the metacharacter is not treated as a metacharacter for that regular expression. It is simply a character or token with no special meaning, just as a numeral has no special meaning. The backslash applies only to the character immediately following it in the regular expression.

On an E-series router, you are likely to use the backslash only for the parentheses characters, ( or ). BGP indicates a segment of an AS path that is of type AS-confed-set or AS-confed-seq by enclosing that segment with parentheses.

Example

The following AS-path access list uses a regular expression to match routes that have an AS-path attribute that begins with any AS-confed-set or AS-confed-seq:



host1(config)#ip as-path access-list 1 permit ^\(

The following AS-path access list uses a regular expression to match routes that have an AS-path attribute that ends with any AS-confed-set or AS-confed-seq:



host1(config)#ip as-path access-list 1 permit \)$

The following AS-path access list uses a regular expression to match routes that have an AS-path attribute that includes the specific AS-confed-set or AS-confed-seq, (100 200):



host1(config)#ip as-path access-list 1 permit \(100 200\)

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