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Forum Discussion

BaltoStar_12467's avatar
BaltoStar_12467
Mar 07, 2015

BIG-IP : iRule test that variable exists and has certain value

F5 BIG-IP Virtual Edition v11.4.1 (Build 635.0) LTM on ESXi What is the simplest most elegant syntax to test that a variable exists and has a certain value ? For example if I want to determine t...
application delivery
design
devops
irule
iRules
LTM
variable
Kai_Wilke's avatar
Kai_Wilke
Icon for MVP rankMVP
Dec 14, 2016

Hi BaltoStar,

if the given variable exists in 90% of the cases, then 

[catch {}]
will do an awesome job...

when HTTP_REQUEST {
    if { [catch {
        if { $variable } then {
            log local0.debug "The variable does exist and has a value of 1"     
        }
    }] } then {
        log local0.debug "The variable does not exists."        
    }   
}

... but if the variable exists in less than 90% of the cases, then 

[info exists]
will start to outperform 
[catch {}]
.

when HTTP_REQUEST {
    if { ( [info exists variable] )
     and ( $variable ) } then {
            log local0.debug "the variable does exist and has a value of 1"     
    } else {
        log local0.debug "The variable does not exists or has an value other than 1."       
    }
}

Note: The reson for this is that a successful 

[catch {}]
command is slightly faster than 
[info exists]
but on the other hand an unsuccessful 
[catch {}]
command is much slower than 
[info exists]
.

Cheers, Kai