This function both works as a filter and can extract new fields using a regular expression. The regular expression can contain one or more named capturing groups. Fields with the names of the groups will be added to the events. Using " in already quoted strings requires escaping. This is sometimes necessary when writing regular expressions.

LogScale uses JitRex which closely follows — but does not entirely replicate — the syntax of RE2J regular expressions, which is very close to Java's regular expressions. See Regular Expression Syntax for more information.

Note

To ensure compatibilty, it is recommended to always test your regular expressions inside LogScale, instead of a 3rd party regex tool.

ParameterTypeRequiredDefaultDescription
fieldstringoptional[a]@rawstring Specifies the field to run the regular expression against.
flagsstringoptional[a]m Specifies regex modifier flags.
  Valid ValuesdPeriod (.) also includes newline characters
   iIgnore case for matched values
   mMulti-line parsing of regular expressions
limitintegeroptional[a]100 Defines the maximum number of events to produce. A warning is produced if this limit is exceeded, unless the parameter is specified explicitly.
regex[b]stringrequired  Specifies a regular expression. The regular expression can contain one or more named capturing groups. Fields with the names of the groups will be added to the events.
repeatbooleanoptional[a]false If set to true, multiple matches yields multiple events.
  Valid ValuesfalseMatch at most one event
   trueMatch multiple events
strictbooleanoptional[a]true Specifies if events not matching the regular expression should be filtered out of the result set.
  Valid ValuesfalseEvents not matching the regular expression are not filtered out then the regex matches.
   trueEvents not matching the regular expression are filtered out of the result set.

[a] Optional parameters use their default value unless explicitly set

[b] The argument name regex can be omitted.

Omitted Argument Names

The argument name for regex can be omitted; the following forms of this function are equivalent:

logscale
regex("value")

and:

logscale
regex(regex="value")

Important

The regex() provides similar functionality to the /regex/ syntax, however, the regex() function searches specific fields (and only @rawstring by default). In contrast, the /regex/ syntax searches all sent and parsed fields and @rawstring.

If you specify a field with the /regex/ syntax, the search is limited only to those field, for example:

| sessionid = /sess/

Limits the search to only the specified field.

The difference in search scope between the two regex syntax operations introduces a significant performance difference between the two. Using regex() searches only the specified field (@rawstring by default) and can be significantly more performant than the /regex/ syntax depending on the number of fields in the dataset.

Attention

When performing queries, the g option — used for global, as in repeating — is allowed in a query, but is not an acceptable option for the flags parameter. To use one of the parameters for multiple matches, you should instead set the repeat parameter to true.

For more information, see Global (Repeating) Matches.

regex() Examples

Extract the domain name of the http referrer field. Often this field contains a full url, so we can have many different URLs from the same site. In this case we want to count all referrals from the same domain. This will add a field named refdomain to events matching the regular expression.

logscale
regex("https?://(www.)?(?<refdomain>.+?)(/
| $)", field=referrer)
| groupby(refdomain, function=count())
| sort(field=_count, type=number, reverse=true)

Extract the user id from the url field. New fields are stored in a field named userid.

logscale
regex(regex="/user/(?<userid>\\S+)/pay", field=url)

Show how to escape " in the regular expression. This is necessary because the regular expression is itself in quotes. Extract the user and message from events like: Peter: "hello" and Bob: "good morning".

logscale
regex("(?<name>\\S+): \"(?<msg>\\S+)\"")

Note

There are no default flags for a regular expression. For example:

logscale
@rawstring=/expression/

Is syntactically equivalent to:

logscale
regex("expression")

Or:

logscale
regex("expression", flags="")

When using flags:

logscale
@rawstring=/expression/m

Is syntactically equivalent to:

logscale
regex("expression", flags="m")