calling system applications / command disabled

Some TCL commands are disabled in iRules, like

 

set sc [open "| /usr/bin/command"]

 

 

I get the error:

 

line 1: [command is not valid in the current scope] [set sc [open "| /usr/bin/command"]]

 

line 1: [command is disabled: "open"] [open "| /usr/bin/command"]

 

 

So is there a list of disabled commands?

 

 

Also, if I have a script written in PERL on the system, and I want my iRule to execute it to receive a status of a node to be used in evaluation in the iRule, how can I execute the script and import the resulting output if open is disabled?

 

 

-RG