Regular Expression Guide

Regular Expressions or regex are a sequence of characters that forms a pattern used to search character combinations in string values.

This article serves as a guide on how to write regex for some Strato features that may need regex values.

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This article is not an exhaustive list of regular expression syntax. For an exhaustive guide, consult the official Java 8 regex syntax.

To play around with regex before implementing in your Strato instance, use sites like regex101 and set your flavor to Java 8.

Tokens and Characters

To get a specific character, type the exact character.
To get only a specific range of characters, type the range in square brackets [].
- Examples:
  - [a-z] targets lowercase characters.
  - [A-Z] targets uppercase characters.
  - [a-zA-Z] targets both lowercase and uppercase characters.
  - [0-9] targets digits from 0 to 9.
There are specific shorthands that target certain character classes:
- \d targets digits from 0 to 9. Equivalent to [0-9].
- \w targets word characters. This includes lowercase and uppercase characters, digits, and underscores. Equivalent to [a-zA-Z0-9_].
- \s targets whitespace characters. This includes tabs, spaces, and new line characters.
- \D is the opposite of \d and targets anything that is not a digit.
- \W is the opposite of \w and targets anything that is not a word character.
- \S is the opposite of \s and targets anything that is not a whitespace character.
To get any character except line breaks, type a period ..
To get any special character by itself, type a backslash \ first before the special character.
- Examples:
  - \. targets a period.
  - \\ targets a backslash.
  - \( targets an open parenthesis.

Quantifiers

Quantifiers determine how many characters should be taken.

Specific

You can specify numbers in a quantifier using curly brackets {}.

To get an exact number of characters, type a number inside the curly brackets.
- Example: \D{5} targets five non-digit characters.
To get an X to Y number of characters, type two numbers inside the curly brackets separated by a comma.
- Example: \w{5,9} targets five to nine word characters.
To get X or more characters, type a number and a comma inside the curly brackets.
- Example: \d{8,} targets eight or more digits.

Greedy

Greedy quantifiers will select as many characters as possible, and output the longest match.

To get one or more characters, type a plus + after the character.
To get zero or more characters, type an asterisk * after the character.
To get zero or one character, type a question mark ? after the character.

For example, in the string Sales Representative (Malaysia) (Asia), the regex pattern $.+$ will output (Malaysia) (Asia).

Lazy

Lazy quantifiers will select as few characters as possible, and output the shortest match. To make a quantifier lazy, add a question mark ? after any of the specific or greedy quantifiers.

For example, in the string Sales Representative (Malaysia) (Asia), the regex pattern $.+?$ will output (Malaysia) and (Asia) separately.

Modifiers

To create an extraction or capturing group, type your regex pattern inside parentheses (). This will output only what is inside the parentheses.
- Example: In the string Sales Representative (Asia), the regex pattern (.*?)\s*\( will output Sales Representative.
To set the position of your search at the beginning of the string, type a caret ^ at the beginning of your regex pattern.
- Example: In the string Sales Representative, the regex pattern ^(.+?)\s will output Sales.
- a
To set the position of your search at the end of the string, type a dollar sign $ at the end of your regex pattern.
- Example: In the string Sales Representative, the regex pattern \s(.+?)$ will output Representative.