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 the syntax of re2j regular expressions which has a syntax very close to Java's regular expressions. Check out the syntax.

ParameterTypeRequiredDefaultDescription
fieldstringfalse@rawstringSpecifies the field to run the regular expression against. Default is running against @rawstring .
flagsstringfalsemSpecifies other regex flags.
  Valid ValuesdPeriod (.) includes newline characters
   iIgnore case for matched values
   mMulti-line parsing of regular expressions
limitnumberfalsefalseDefines the maximum number of events to produce (defaults to 100). A warning is produced if this limit is exceeded, unless the parameter is specified explicitly.
regexstringtrue 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. [a]
repeatbooleanfalsefalseIf set to true, multiple matches yields multiple events.
  Valid ValuesfalseMatch at most one event
   trueMatch multiple events
strictbooleanfalsetrueSpecifies if events not matching the regular expression should be filtered out of the result set. Strict is the default.

[a] When you provide only one parameter, the implied parameter is regex

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. 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 sginificantly more performant than the /regex/ syntax depending on the number of fields in the dataset.

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.

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 that the default flags for a regular expression is no flags, so that:

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")