Regular Expressions

Regular Expressions Overview

A regular expression, also known as regex, describes a pattern for a string.

This appendix provides some details and tips specific to using regular expressions with the Data Collector. For a thorough description of how to define regular expressions, use a manual or online reference such as: https://docs.oracle.com/javase/tutorial/essential/regex/index.html.

For testing regular expressions, you might find the following website helpful: https://regex101.com/.

Regular Expressions in the Pipeline

Though generally not required, you can use Java-based regular expressions at various locations within a pipeline to define, search for, or manipulate strings.

For example, in the Field Masker processor, you can use a fixed length, variable length, or custom static mask to mask data in a field. When that doesn't work for you, you can use a regular expression to define a specific custom mask. Similarly, you can use a regular expression to define the format of a log line if it does not use one of the listed formats.

The following table describes some examples of how you might use regular expressions in the pipeline:
Location Description
Directory origin Optionally use to define the pattern of the file name.
File Tail origin Use to define the ${PATTERN} constant when you use the Files Matching a Pattern naming option.

Use to define the structure of a log line or text.

Origins that process log data

Log Parser processor

Optionally use to define the pattern of the log line.
Field Masker processor Optionally use to define the field mask.
regexCapture function Use to define the groups and pattern of the string so you can specify the group to return.
replaceAll function Use to define the string to replace.

Quick Reference

The following table includes some details you might find helpful when creating a regular expression:
Character Description Examples
[ ] Use brackets to define character classes. [0-9][0-9][0-9] represents 3 digits ranging from 0 through 9, inclusive.
- Use the hyphen to define ranges.

[a-z] defines one lowercase letter from a to z.

[A-Z] defines one uppercase letter from A to Z.

| Indicates an alternate option to the character or group being defined. [a-z | A-Z] represents a single upper or lowercase letter.
( ) Use parentheses to create groups, atomic groups, or lookarounds. ([0-9][0-9][0-9])(-|.)([0-9][0-9][0-9])(-|.)([0-9][0-9][0-9][0-9]) represents phone numbers with area codes that are separated by dashes or periods as follows: 415-555-5555 and 415.555.5555.
< > Use angle brackets to define named capture groups. Use the following syntax:
(?<groupName> ...) 
to set up a named field extraction.
 
^ Use a carat to negate a character class. [^A-G] defines a character that is not an uppercase letter from A to G.
. A wildcard that represents any single character except newline or other special characters.  
&& Use two ampersands to indicate the union of two ranges. [\w&&[^1-9] represents all word characters except 1-9.
? A quantifier that represents zero or one instance of the preceding character or group. B-?7 represents B7 or B-7.
+ A quantifier that represents one or more instances of the preceding character or group. ([0-9][0-9][0-9])-+([0-9][0-9][0-9][0-9]) represents phone numbers that area codes: 415-555-5555 and 555-5555.
* A quantifier that represents zero or more instances of the preceding character or group. ([0-9][0-9][0-9][0-9][0-9])-([0-9][0-9][0-9][0-9])* represents 5- and 9-digit zip codes.
\ Use the backslash as an escape character.  
\\ Represents a single backslash  
\w Represents a word character - includes alphanumeric characters and the underscore. \w\w\w-\w\w\w\w\w can represent an error code, such as SVR-30243.
\W Represents a non-word character - includes everything except alphanumeric characters and the underscore.  
\d Represents a digit. Shorthand for 0-9. (\d\d\d\d\d)-(\d\d\d\d)* represents a 9-digit zip code.
\D Represents a non-digit character. \D&&\S represents the alphabet in either case.
\s Represents a whitespace character - includes space, tab, line break and form feed.  
\S Represents a non-space character - includes everything except the space, tab, line break, and form feed characters.  
\t Tab character.  
\r Return character.  
\n Line break or newline character.  
\f Form feed character.  

Regex Examples

Masking credit card numbers, except for one group
You can use the following regular expression in the Field Masker to mask all numbers in a credit or debit card except for the last 4 digits:
(.*)([0-9]{4})
This regex defines two groups. The first uses /d* to represent any number, with any number of numbers. And the second group represents the last four digits. In the Field Masker, for the Groups to Show property, you can then enter 2 to display the last 4 digits of a credit card number.
The following regular expressions perform the same task:
(/d*)(/d{4})
(/d*)(/d/d/d/d)