Is there a way in an iRule to determine if an ASM policy exists before doing an ASM::enable on it?

KWH,

It seems like what you are looking for is the iRules 'catch' statement. This will try to run a piece of code and check for any runtime errors. If there is any error, it will run a second block of code instead. This will help you check if a certain policy exists. I haven't properly tested this code, but I believe your solution should look something like this.

if { [catch {
     ASM::enable $policy
     log local0. "$policy was enabled"  
     }] } then {
         This block only triggers if the above code would fail
        log local0. "$policy does not exist"
    }

More information here, if you would like to research some more yourself.