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ROPE Registers

Rope supports the idea of "registers" - these are pretty much the same as scalar variables in perl or C.

The following types of registers are available.
- 26 "user" registers called "$a" through to "$z" or accessed by number using the reg action.
- A number of "internal" registers listed in LanguageReference.
- A set of "global" (public) integer registers, accessed via the "greg" action and the /proc file system.

User registers can hold any of the following Rope data types

Internal system registers can only hold the specific type they are declared in the documentation to contain - ie, it is an error to put a string into an internal integer register.

Global registers can only hold integer values.

Their names start with a "$" and continue with any combination lower case letters, digits and underbars (upper case letters are not used).

When they hold strings, Rope does not copy the string data into the register, but the register holds a pointer (and length) to the string data in some other memory location, which may be..
- In the code of the compiled script (a string constant)
- A portion of the packet being inspected.
- A portion of another string register.
Their contents are accessed using "get" and changed using "put"
Most (but not all) "internal" registers are read-only.
Registers are always accessed "by reference" (see below).

Register References

When a Rope script refers to a user or "internal" register using a dollar character before the register name, Rope actually pushes a value onto the stack that is a reference to the register that was named.

The get action is used to collect the value contained in that register. For example, the following code puts the contents of $a onto the stack. Without the "get" the stack would contain a reference to $a instead of it's value.

$a get

The same logic is also used to collect the values of internal registers, for example.

$ip_saddr get

Rope actions that want to see values on the stack rather than register references perform a "get" internally, so that the following are equivalent:

$x print
$x get print

Some (but by no means all) registers can have their values changed using the "put" action, like this..

20 $x put
put( 13 $offset )

The reg and greg actions provide an alternative way of getting a register reference.

ROPE Registers

Register References

See Also