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Understanding Regular Expressions, Special
Characters, and Patterns
This appendix describes the regular expressions, special or wildcard characters, and patterns that can be
used with filters to search through command output. The filter commands are described in the
show Command Output" section on page
filters:
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Regular Expressions
A regular expression is a pattern (a phrase, number, or more complex pattern):
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A regular expression can be a single-character pattern or multiple-character pattern. That is, a regular
expression 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 referred to as 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.
OL-10957-02
Regular Expressions, page A-1
Special Characters, page A-2
Character Pattern Ranges, page A-2
Multiple-Character Patterns, 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 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.
A P P E N D I X
6-9. The following sections describe features you can use with
Cisco IOS XR Getting Started Guide
A
"Filtering
A-1
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