Chapter 4 Advanced Expressions: Evaluating Text 65
In the preceding examples, the contains operator permits a partial match and
the eq operator looks for an exact match.
Other operations are available to format the string before evaluating it, for
example, to strip out quotes and white spaces, to convert the string to all
lowercase, or to concatenate strings.
Note: Complex operations are available to perform matching based on patterns
or to convert one type of text format to another type. For more information, see
“Advanced Expressions: String Sets, String Patterns, and Data Formats,” on page
157.
Compounding and Precedence in Text Expressions
You can apply various operators to combine text prefixes or expressions. For
example, the following expression concatenates the returned values of each
prefix:
http.req.hostname + http.req.url
Following expression is an example of forming a compound text expression that
uses a logical AND. In this example, both components of the expression must be
TRUE for a request to match the expression:
http.req.method.eq(post) && http.req.body(1024).
startswith("destination=")
Note: For more information on operators for compounding, see “Compound
Advanced Expressions,” on page 45.
Categories of Text Expressions
The primary categories of text expressions that you can configure are:
• Information in HTTP headers, HTTP URLs, and the POST body in HTTP
requests.
For more information, see “Expression Prefixes for Text in HTTP Requests
and Responses,” on page 67.
• Information regarding a VPN or a clientless VPN.
For more information, see “Expression Prefixes for VPNs and Clientless
VPNs,” on page 76.
• TCP payload information.