Cisco Systems A9KMOD80TR Understanding Regular Expressions, Special Characters, and Patterns

F I N A L D R A F T — C i s c o C o n f i d e n t i a l

A P P E N D I X A

Understanding Regular Expressions, Special Characters, and Patterns

This appendix describes regular expressions, special or wildcard characters, and patterns used with filters to search through command output. Filter commands are described in the “Filtering show Command Output” section on page 5-9.

Contents

•Regular Expressions, page A-1

•Special Characters, page A-2

•Character Pattern Ranges, page A-2

•Multiple-Character Patterns, page A-3

•Complex Regular Expressions Using Multipliers, page A-3

•Pattern Alternation, page A-4

•Anchor Characters, page A-4

•Underscore Wildcard, page A-4

•Parentheses Used for Pattern Recall, page A-4

Regular Expressions

A regular expression is a pattern (a phrase, number, or more complex pattern).

•Regular expressions are case sensitive and allow for complex matching requirements. Simple regular expressions include entries like Serial, misses, or 138.

•Complex regular expressions include entries like 00210... , ( is ), or [Oo]utput.

Aregular expression can be a single-character pattern or multiple-character pattern. It can be a single character that matches the same single character in the command output or multiple characters that match the same multiple characters in the command output. The pattern in the command output is called a string.

The simplest regular expression is a single character that matches the same single character in the command output. Letter (A–Z and a–z), digits (0–9), and other keyboard characters (such as ! or ~) can be used as a single-character pattern.

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