Cisco Systems A9K24X10GETR, ASR 9000, A9KMOD80TR Multiple-Character Patterns, ba?b, A-Za-z0-9+

Appendix A Understanding Regular Expressions, Special Characters, and Patterns

Multiple-Character 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

Multiple-Character Patterns

Multiple-character regular expressions can be formed by joining letters, digits, and keyboard characters that do not have a special meaning. With multiple-character patterns, order is important. The regular expression a4% matches the character a followed by a 4 followed by a %. If the string does not have a4%, in that order, pattern matching fails.

The multiple-character regular expression a. uses the special meaning of the period character to match the letter a followed by any single character. With this example, the strings ab, a!, and a2 are all valid matches for the regular expression.

Put a backslash before the keyboard characters that have special meaning to indicate that the character should be interpreted literally. Remove the special meaning of the period character by putting a backslash in front of it. For example, when the expression a\. is used in the command syntax, only the string a. is matched.

A multiple-character regular expression containing all letters, all digits, all keyboard characters, or a combination of letters, digits, and other keyboard characters is a valid regular expression. For example: telebit 3107 v32bis.

Complex Regular Expressions Using Multipliers

Multipliers can be used to create more complex regular expressions that instruct Cisco IOS XR software to match multiple occurrences of a specified regular expression. Table A-2lists the special characters that specify “multiples” of a regular expression.

Table A-2	Special Characters Used as Multipliers
Character		Description
*		Matches 0 or more single-character or multiple-character patterns.
+		Matches 1 or more single-character or multiple-character patterns.
?		Matches 0 or 1 occurrences of a single-character or multiple-character pattern.

The following example matches any number of occurrences of the letter a, including none:

a*

The following pattern requires that at least one occurrence of the letter a in the string be matched:

a+

The following pattern matches the string bb or bab:

ba?b

The following string matches any number of asterisks (*):

\**

To use multipliers with multiple-character patterns, enclose the pattern in parentheses. In the following example, the pattern matches any number of the multiple-character string ab:

(ab)*

As a more complex example, the following pattern matches one or more instances of alphanumeric pairs:

([A-Za-z][0-9])+

Cisco ASR 9000 Series Aggregation Services Router Getting Started Guide

OL-17502-01 A-3