Some analytic workflows have a dynamic behaviour - for example, skipping a step based on the user input. Thus, this kind of workflow can not be represented by a static sequence of steps. To overcome this issue, WDL understands also some basic directives, which can be used to create steps. By using conditions and loops inside the WDL file the steps of a workflow can be constructed in a dynamic way based on the user input.
Each directive starts with # and has to be at beginning of a line.
You can use every input parameter (in this example
$choice) to build logical conditions. More about conditions and syntax examples can be found in the Velocity manual.
id: if-example name: IF Condition Example version: 1.0 workflow: steps: #if ($choice == "yes") - name: Yes Step cmd: /bin/echo yes select stdout: true #end #if ($choice == "no") - name: No Step cmd: /bin/echo no select stdout: true #end inputs: - id: choice description: Select a value values: no: No yes: Yes type: list
You can use loops to add steps to your workflow dynamically:
id: loop-example name: Loop Example version: 1.0 workflow: steps: #foreach($i in [1..10]) - name: Step $i cmd: /bin/echo I am step number $i stdout: true #end