Configurable rule that has the cron specification parameterized

[marian.tudor]

• Platform information:

  • Hardware: RPI3B
  • OS: OPENHABIAN
  • openHAB version: openHAB 2.5.10-1

• Issue of the topic:

  Hello,
  Please let me know how I can use a variable inside a CRON expresion. I want to have the option to configure the starting time and ending time from the user interface perspective.
  So, for example a have this rule:

rule “All lamps on”
when Time cron “0 0 6 ? * MON-FRI *”
then all_lights_on_on.sendCommand(“ON”)
logInfo(“info”,“all lights on rule fired”)
end

And I want to modify the value 6 - (rule to be considered from 6 AM).

Until now I found this post / solution that is from '15. Maybe do you know other approach / workaround:

Variable in cron

I like this approch the best. Though you will want some logic on System Started to recreate the timer in the event of an openHAB restart. Sounds like a good reason to use the JSR223 rules engine. This gets asked often enough perhaps it is worth adding it as an example to the wiki.

Thank you in advance

[rossko57]

@marian.tudor

Please let me know how I can use a variable inside a CRON expresion.

You cannot.

Cron rule controled by the user

You can’t. Cron expressions used to trigger rules are fixed and hard coded. For OH 2.5 see one of the many Alarm Clock examples posted here to the forum. For OH 3, create a DateTime Item, configure the card per OH 3 Examples: How to boot strap the state of an Item. When that Item changes trigger a rule to set a Timer to do the actions at the time chosen. An additional way to handle stuff like this includes the Time of Day Design Pattern. There is even a couple of versions of that you can just…

[marian.tudor]

Thank you for prompt answer!

[pacive (Anders Alfredsson)]

With the Jruby scripting addon, you can!
dynamic_rule.tems:

String Cron_Expr "Cron expression for dynamic rule"

dynamic_rule.rb

require 'openhab'

def dynamic_rule(name, cron_expr, &block)
  remove_rule(name)
  rule name do
    cron cron_expr
    run block
  end
end

def remove_rule(name)
  rules = $se.get('ruleRegistry')
  rules.get_all.select { |rule| rule.name.match?(name) }.each { |rule| rules.remove(rule.uid) }
end

rule 'Update cron rule' do
  changed Cron_Expr
  run do
    dynamic_rule('Dynamic cron rule', Cron_Expr) do
      # Rule body here
    end
  end
end

Update the Cron_Expr Item with a valid cron expression and the rule will be recreated with the new value.
Just make sure you use unique names for your rules, otherwise you might delete the wrong one.