&Attribute References

Attributes may be referenced via the following syntax:

Syntax

&Attribute-Name
&Attribute-Name:TAG
&Attribute-Name[NUM]
&<list>:Attribute-Name
&<list>:Attribute-Name:TAG[NUM]

The &Attribute-Name operator returns a reference to the named attribute.

When used as an existence check in a condition, the condition evaluates to true if the attribute exists. Otherwise, the condition evaluates to false.

When used elsewhere, such as in switch, it returns the value of the named attribute.

Examples

&User-Name
&NAS-IP-Address

Lists

The attribute reference can also be qualified with a list reference. When no list is given, the server looks in the input packet list for the named attribute.

Examples

&request:User-Name
&reply:NAS-IP-Address

Array References

Finding a particular attribute from multiple instances can be done via an array reference.

Syntax

&Attribute-Name[<integer>]

When an attribute appears multiple times in a list, this syntax allows you to address the attributes as if they were array entries. The <integer> value defines which attribute to address. The [0] value refers to the first attributes, [1] refers to the second attribute, etc.

Examples

&EAP-Message[1]
&reply:NAS-IP-Address[2]

Other Array indexes

The array syntax can be used for a few special cases, too.

Syntax

&Attribute-Name[#]
&Attribute-Name[*]
&Attribute-Name[n]

These extra fields have the following definitions:

#: Returns an integer which is the number of instances of this attribute.
*: Returns all of the instances of the given attribute. This syntax can only be used in a string expansion. It will return all of the values of the attribute, separated by commas.
n: Returns the last instance of the given attribute.

Removing ambuguity from the configuration files

In most cases, the server uses the & character to distinguish attribute names from other strings.

Without the &, it is more difficult to parse the configuration file clearly. You could interpret a string as hello-there either as a literal string "hello-there", or as a reference to an attribute named hello-there.

Adding the leading & character means that attribute references are now easily distinguishable from literal strings. The use of the leading & character is highly recommended.