In the examples associated with this article, we provide tool descriptions that illustrate how to print custom greetings at the command line. These diagrams illustrate the 02_hello.cwl (A) and 03_hello.cwl (B) examples. In (A), the tool description indicates which inputs that must be specified, along with a template for executing the command; it also indicates that a message will be printed to standard output and that this message should be stored in a file called 02_output.txt. The hello_objects_age.yml input-object file stores values for a particular invocation of the tool. In (A), the cwltool workflow engine uses the host computer’s operating system to execute the tool; thus, the echo command must be supported on that operating system. In (B), the tool description defines a software container environment; thus, cwltool executes the command within a container, which provides the echo command (packaged with the Debian Linux operating system).