A regular expression (sometimes shortened to “regex” or “regexp”) is a pattern that can match some set of strings, and optionally capture parts of those strings for further use.
You can use regular expression values
with the =~ and !~ match operators, case statements and selectors, node definitions, and
functions like regsubst for editing strings, or match for capturing and extracting substrings. Regular expressions
act like any other value, and can be assigned to variables and used in function
arguments.
Syntax
/node
.*/m.if $host =~ /^www(\d+)\./ {
notify { "Welcome web server #$1": }
}%r{^www(\d+)\.}, are not allowed. You cannot interpolate
variables or expressions into regex values.If you are matching
against a string that contains newlines, use \A and \z instead of ^ and $, which match the beginning and end of a line. This is a common mistake that
can cause your regexp to unintentionally match multiline text.
Some places in the language accept both real regex values and stringified regexes — that is, the same pattern quoted as a string instead of surrounded by slashes.
Regular expression options
(?<ENABLED
OPTION>:<SUBPATTERN>) and (?-<DISABLED
OPTION>:<SUBPATTERN>) notation. The following example enables
the i option
while disabling the m and x options:$packages = $operatingsystem ? {
/(?i-mx:ubuntu|debian)/ => 'apache2',
/(?i-mx:centos|fedora|redhat)/ => 'httpd',
}- i
- Ignore case.
- m
- Treat a new line as a character matched by
. - x
- Ignore whitespace and comments in the pattern.
Regular expression capture variables
Within conditional
statements and node
definitions, substrings withing parentheses () in a regular expression are available as numbered variables
inside the associated code section. The first is $1, the second is $2, and so on. The entire match is available as $0.
The values of the numbered variables do not persist outside the code block associated with the pattern that set them.
You can’t manually assign values to a variable with only digits in its name; they can only be set by pattern matching.
In nested conditionals, each conditional has its own set of values for the set of numbered variables. At the end of an interior statement, the numbered variables are reset to their previous values for the remainder of the outside statement. This causes conditional statements to act like local scopes, but only with regard to the numbered variables.
The Regexp data type
The data type of regular expressions
is Regexp. By
default, Regexp matches any regular expression value. If you are looking for a type
that matches strings which match arbitrary regular expressions, see
the Pattern type. You can use parameters to restrict which values Regexp matches.
Parameters
Regexp is:Regexp[<SPECIFIC REGULAR EXPRESSION>]| Position | Parameter | Data type | Default value | Description |
|---|---|---|---|---|
| 1 | Specific regular expression | Regexp |
none | If specified, this results in a data type that only matches one specific regular expression value. Specifying a parameter here doesn’t have a practical use. |
Regexp- Matches any regular expression.
Regexp[/<regex>/]- Matches the regular expression
/<regex>/only.
Regexp matches only literal regular expression
values. Don't confuse it with the abstract Pattern data type, which uses a
regular expression to match a limited set of String values.