Regular Expression Syntax Used in Patterns

A Pattern represents a regular expression (regex), a sequence of characters typically used to perform a pattern match.

This topic summarizes the use of the most common regex characters that can be used when you are adding or editing a Project Pattern.

Pattern Syntax

Any character matches itself in a pattern unless the character is one of the designated special characters. To override the designated meaning of a special character and treat it as the literal character, you must precede the character with the escape character \. The following are regex special characters:

. [ ] { } ( ) \ * + ? | ^ $ '

Any single character or marked subexpression can be repeated with the *, +, ?, and {} operators.

Digital Reef supports the java.util.regex package.

Summary of Selected Special Characters

Character	Behavior
. (period or dot)	Character match – When used outside of a character set matches any single character. When used inside a bracket set (a Pattern starting with [ and ending with ] that defines a set of characters), matches any single character that is a member of that set.
\ (backslash)	Escapes a special character – Put an escape character before any character that you want to include as a literal in the Pattern. For example, to match c:\, type the Pattern as c:\\. To match [note], type \[note\].
[ ] (brackets)	Character Set – Defines a character set. A bracketed-Pattern starts with [ and ends with ]. Defines a set of characters and matches any single character that is a member of that set. For example, to match a character using a character range: [a-z].
{ } (braces)	Grouping – A single character or marked subexpression can be repeated with a bounded repeat. Examples: a{n} matches 'a' repeated exactly n times. a{n,} matches 'a' repeated n or more times. a{n,m} matches 'a' repeated between n and m times inclusive.
( ) (parenthesis)	Grouping – Used to group alternatives (for example, ab(d|ef) will match either of abd or abef).
* (asterisk)	Quantifier – Match the preceding single character or marked subexpression zero or more times. For example the expression a*b will match any of the following: b ab aaaaaaaab
+ (plus)	Quantifier – Match the preceding single character or marked subexpression one or more times. For example the expression a+b matches any of ab and aaaaaaaab but not b.
? (question mark)	Quantifier – Match the preceding single character or marked subexpression zero times or one time. For example, the expression ca?b will match cb or cab but not caab.
| (pipe)	OR operator – Matches either of its arguments. Examples: abc|def matches either abc or def.
^ (caret)	Position – Matches the start of a line (start of a term).
$ (dollar sign)	Position – Matches the end of a line (end of a term).
\b	Word Boundary – Indicates a word boundary.
\d	Digit – Represents any digit, that is, any of 0 1 2 3 4 5 6 7 8 9.
(?i)	Pattern Modifier - Case insensitive.