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Erik_27939's avatar
Erik_27939
Icon for Nimbostratus rankNimbostratus
Aug 20, 2014
Solved

How do you handle a null variable in an irule?

I am using the below logic:

    if { [string length $sort_dest_pool] > 0 } {
        set dest_pool [string trimleft $sort_dest_pool "$loc"]
    } else {
        set dest_pool $orig_pool
    }

If $sort_dest_pool is not defined, I get the following error/event:

can't read "sort_dest_pool": no such variable while executing "string length $sort_dest_pool"

According to this error, it is failing while trying to get the string length. This method was suggested as the solution for testing a string to see if it is set. Any ideas?

application delivery
devops
iRules
LTM
  • nitass_89166's avatar
    nitass_89166
    Aug 21, 2014

    can you try to remove $?

    e.g.

    % info exists t
0
% set t 1
1
% info exists t
1

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  • Erik_27939's avatar
    Erik_27939
    Icon for Nimbostratus rankNimbostratus
    Aug 21, 2014

    Unfortunately, now I am getting this error:

    can't read "sort_dest_pool": no such variable while executing "info exists $sort_dest_pool"

    Based on that man page you sent on that command, it should have worked. Thoughts?

  • nitass_89166's avatar
    nitass_89166
    Icon for Noctilucent rankNoctilucent
    Aug 21, 2014

    can you try to remove $?

    e.g.

    % info exists t
0
% set t 1
1
% info exists t
1
  • nitass's avatar
    nitass
    Icon for Employee rankEmployee
    Aug 21, 2014

    can you try to remove $?

    e.g.

    % info exists t
0
% set t 1
1
% info exists t
1
  • hooleylist's avatar
    hooleylist
    Icon for Cirrostratus rankCirrostratus
    Aug 22, 2014

    Yep, you can use [info exists varname] to check if a variable is defined. Or you could set it to a null value by default and then check it later to see if it's not null:

    when HTTP_REQUEST {

    if {$some_condition == 1}{
        set sort_dest_pool "my_pool"
    } else {
        set sort_dest_pool ""
    }

     later...

    if {$sort_dest_pool eq ""}{
         Take some default action
    } else {
        pool $sort_dest_pool
    }
}

    Aaron