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Use Regular Expressions to Refine the Set of Events That Trigger a Policy

You can use regular expression matching to specify more exactly which events cause a policy to be executed.

To specify the text string that must appear in an event attribute for the policy to be executed, include the matches statement at the [edit event-options policy policy-name attributes-match] hierarchy level, and specify the regular expression that the event attribute must match:

When you specify the regular expression, use the notation defined in POSIX Standard 1003.2 for extended (modern) UNIX regular expressions. Explaining regular expression syntax is beyond the scope of this document. Table 1 specifies which character or characters are matched by some of the regular expression operators that you can use in the matches statement. In the descriptions, the term term refers to either a single alphanumeric character or a set of characters enclosed in square brackets, parentheses, or braces.

Note:

The matches statement is not case-sensitive.
Table 1: Regular Expression Operators for the matches Statement

Operator

Matches

. (period)

One instance of any character except the space.

* (asterisk)

Zero or more instances of the immediately preceding term.

+ (plus sign)

One or more instances of the immediately preceding term.

? (question mark)

Zero or one instance of the immediately preceding term.

| (pipe)

One of the terms that appear on either side of the pipe operator.

! (exclamation point)

Any string except the one specified by the expression, when the exclamation point appears at the start of the expression. Use of the exclamation point is specific to Junos OS.

^ (caret)

The start of a line, when the caret appears outside square brackets.

One instance of any character that does not follow it within square brackets, when the caret is the first character inside square brackets.

$ (dollar sign)

The end of a line.

[ ] (paired square brackets)

One instance of one of the enclosed alphanumeric characters. To indicate a range of characters, use a hyphen ( - ) to separate the beginning and ending characters of the range. For example, [a-z0-9] matches any letter or number.

( ) (paired parentheses)

One instance of the evaluated value of the enclosed term. Parentheses are used to indicate the order of evaluation in the regular expression.

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