Validate syntax

Nobody likes to kick off a bunch of jobs only to find after returning from lunch that they all failed within minutes due to a syntax error in the script.

The good news is that WDL comes with a utility toolkit called WOMtool that includes a syntax validation function. You can find instructions for getting and running the WOMtool executable in the WOMtool documentation (but don't worry about it now -- we'll give you that link again when it's time to install everything you need).

To validate our WDL syntax, we simply call the validate function on our script:

$ java -jar wdltool.jar validate myWorkflow.wdl

This function parses the WDL script and alerts us to any syntax errors such as missing curly braces, undefined variables, missing commas, and so on. It will resolve imports, but note that it is not able to identify errors like typos in commands, incorrect filenames, or missing required inputs to the programs that are run in the workflow.

Example WOMtool validate error

Below is an example error message from WOMtool if the WDL workflow calls a task that hasn't been defined:

$ java -jar wdltool.jar validate myWorkflow.wdl

ERROR: Call references a task (BADps) that doesn't exist (line 22, col 8)

  call BADps
       ^

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Once we've fixed any syntax errors, we're almost ready to run our script! Just one more step stands between us and execution. Um. That's a little worrying, isn't it? Maybe we could rephrase that? Sure. Just one more step between us and nirvana. No that's not better. OK, just one more step between us and the satisfaction of a well-written WDL script running smoothly on our preferred execution engine. Yeah alright let's go with that.

Go to the next section: Specify Inputs.