Additional Arguments and Parameters


Teaching: 10 min
Exercises: 0 min
  • How do I specify arguments that don’t require input values?

  • How do I refer to runtime parameters?

  • Learn how to add additional options to a command.

  • Learn how to reference runtime parameters.

Sometimes tools require additional command line options that don’t correspond exactly to input parameters.

In this example, we will wrap the Java compiler to compile a java source file to a class file. By default, “javac” will create the class files in the same directory as the source file. However, CWL input files (and the directories in which they appear) may be read-only, so we need to instruct “javac” to write the class file to the designated output directory instead.


#!/usr/bin/env cwl-runner

cwlVersion: v1.0
class: CommandLineTool
label: Example trivial wrapper for Java 9 compiler
    dockerPull: openjdk:9.0.1-11-slim
baseCommand: javac
arguments: ["-d", $(runtime.outdir)]
    type: File
      position: 1
    type: File
      glob: "*.class"


  class: File

Now create a sample Java file and invoke cwl-runner providing the tool wrapper and the input object on the command line:

$ echo "public class Hello {}" >
$ cwl-runner arguments.cwl arguments-job.yml
[job arguments.cwl] /tmp/tmpwYALo1$ docker \
 run \
 -i \
 --volume=/home/peter/work/common-workflow-language/v1.0/examples/ \
 --volume=/tmp/tmpwYALo1:/var/spool/cwl:rw \
 --volume=/tmp/tmpptIAJ8:/tmp:rw \
 --workdir=/var/spool/cwl \
 --read-only=true \
 --user=1001 \
 --rm \
 --env=TMPDIR=/tmp \
 --env=HOME=/var/spool/cwl \
 openjdk:9.0.1-11-slim \
 javac \
 -d \
 /var/spool/cwl \
Final process status is success
  "classfile": {
    "size": 416,
    "location": "/home/example/Hello.class",
    "checksum": "sha1$2f7ac33c1f3aac3f1fec7b936b6562422c85b38a",
    "class": "File"

Here we use the arguments field to add an additional argument to the command line that isn’t tied to a specific input parameter.

arguments: ["-d", $(runtime.outdir)]

This example references a runtime parameter. Runtime parameters provide information about the hardware or software environment when the tool is actually executed. The $(runtime.outdir) parameter is the path to the designated output directory. Other parameters include $(runtime.tmpdir), $(runtime.ram), $(runtime.cores), $(runtime.outdirSize), and $(runtime.tmpdirSize). See the Runtime Environment section of the CWL specification for details.

Key Points

  • Use the arguments section to describe command line options that do not correspond exactly to input parameters.

  • Runtime parameters provide information about the environment when the tool is actually executed.

  • Runtime parameters are referred under the runtime namespace.