Cisco Systems ASR 9000 Manual De Usuario
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-3
Cisco ASR 9000 Series Aggregation Services Router Getting Started Guide
OL-17502-01
Appendix A Understanding Regular Expressions, Special Characters, and Patterns
Multiple-Character Patterns
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.
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.
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.
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.
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.
to match multiple occurrences of a specified regular expression.
lists the special characters
that specify “multiples” of a regular expression.
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:
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])+
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.