Regular Expressions

Introduction

A regular expression resource document is used in the validation rules of an entity to describe a set of criteria that a string must match.

A regular expression has the properties described below.

Common

Name

The name can be used to refer to the regular expression from a validation rule of an entity.

Documentation

This is for documentation purpose only; it is not visible in the end-user application that you are modeling.

Expression

The expression defines the criteria that a string should be checked against in a formal, internationally standardized regular expression language.

The following sections give a summary of regular expressions that can be used in Mendix. This description also applies to regular expression strings used in functions such as isMatch().

Subexpressions

A regular expression consists of a sequence of subexpressions. A string matches a regular expression if all parts of the string match these subexpressions in the same order.

A regular expression can contain the following types of subexpressions:

• [ ] – a bracket expression matches a single character that is indicated within the brackets, for example:

  • [abc] matches “a”, “b”, or “c”
  • [a-z] specifies a range which matches any lowercase letter from “a” to “z”
  These forms can be mixed: [abcx-z] matches “a”, “b”, “c”, “x”, “y”, or “z”, and is equivalent to [a-cx-z]. The - character is treated as a literal character if it is the last or the first character within the brackets, or if it is escaped with a backslash (</code>).

• [^ ] – matches a single character that is NOT contained within the brackets, for example:

  • [^abc] matches any character other than “a”, “b”, or “c”
  • [^a-z] matches any single character that is not a lowercase letter from “a” to “z”
  As above, literal characters and ranges can be mixed.

• {m,n} – matches the preceding element at least m and not more than n times, for example:

  • a{3,5} matches only “aaa”, “aaaa”, and “aaaaa”

• {n} – matches the preceding element exactly n times, for example:

  • [1-9][0-9]{3} ?[A-Za-z]{2} is an alternative way to write the expression for checking the Dutch post code in the example above

• . – a dot matches any single character; if you want to match a dot, you can escape it by prefixing it with a \ (backslash)

• A literal character – this is a character that does not have a special meaning in the regular expression language and it matches itself; this is effectively any character except \[](){}^-$?*+|., for example:

  • The space in the Dutch post code example is a literal character that just matches itself
  If you need to match one of the characters which is not a literal, prefix it with a backslash (</code>).

• \w – a word: a letter, digit, or underscore; \w is an abbreviation for [A-Za-z0-9_]

• \d – a digit" an abbreviation for [0-9]