Regular_Expressio介绍ns_正则表达式.pdf

Regular Expressions This appendix explains regular expressions and how to use them in Cisco IOS software commands. It also provides details for composing regular expressions. This appendix has the following sections: • General Concepts About Regular Expressions • Cisco Regular Expression Pattern Matching Characters • Single-Character Patterns • Multiple-Character Patterns • Multipliers • Alternation • Anchoring • Parentheses for Recall • Regular Expression Examples General Concepts About Regular Expressions A regular expression is entered as part of a command and is a pattern made up of symbols, letters, and numbers that represent an input string for matching (or sometimes not matching). Matching the string to the specified pattern is called pattern matching . Pattern matching either succeeds or fails. If a regular expression can match two different parts of an input string, it will match the earliest part first. Cisco configurations uses regular expression pattern matching in several implementations. The following is a list of some of these implementations: • BGP IP AS-path and X.29 access lists • Modem (or chat) and system scripts • X.25 route substitute destination feature • Protocol translation ruleset scripts Cisco IOS Terminal Services Configuration Gui