# Regular Expression Configuration

## Contents
Overview

## Overview
Regular expressions are strings (or patterns) that match a set of strings or patterns. For example, it is possible to write regular expressions that match all email addresses, alphabetic characters only, or even IP addresses. The Enterprise Gateway can use such regular expressions to ensure that HTTP header values and/or query string attribute values conform to configured patterns. For example, it is possible to configure a regular expression to make sure that the value of a "User" HTTP header or a "User" query string attribute is a valid email address. To illustrate this, let's look at how the regular expression can be applied to both cases: HTTP Header:
     POST /services/getEmployee HTTP/1.1
     Content-Type: text.html
     User: user@oracle.com
Query String:
    http://hostname.com/services/getEmployee?User=user@oracle.com
The following regular expression can be used to ensure that both the header and attribute values conform to the standard email format:
    \b[a-zA-Z0-9._%-]+@[a-zA-Z0-9._%-]+\.[a-zA-Z]{2,4}\b
To learn how to configure regular expressions for the respective request parameters, click on the appropriate link below: Query String Validation HTTP Header Validation