Cisco Systems A9K24X10GETR Guide de démarrage rapide télécharger pdf (Page 141)

FINAL DRAFT —Cisco Confidential

A-5

Cisco ASR 9000 Series Aggregation Services Router Getting Started Guide

OL-17502-01

Appendix A Understanding Regular Expressions, Special Characters, and Patterns

Parentheses Used for Pattern Recall

To create a regular expression that recalls a previous pattern, use parentheses to indicate memory of a

specific pattern and a backslash (\) followed by a digit to reuse the remembered pattern. The digit

specifies the occurrence of a parenthesis in the regular expression pattern. When there is more than one

remembered pattern in the regular expression, \1 indicates the first remembered pattern, \2 indicates the

second remembered pattern, and so on.

The following regular expression uses parentheses for recall:

a(.)bc(.)\1\2

This regular expression matches an a followed by any character (call it character number 1), followed by

bc followed by any character (character number 2), followed by character number 1 again, followed by

character number

2 again. So, the regular expression can match aZbcTZT. The software remembers that

character number

1 is Z and character number 2 is T, and then uses Z and T again later in the regular

expression.

1 2 ... 136 137 138 139 140 141 142

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Cisco Systems A9K24X10GETR Guide de démarrage rapide Page 141