Lesson 2 - First Operation

Goal

In this lesson we’ll write our first operation. We’ll learn the basic structure of a simple operation by writing one that simply prints out a message.

Get Started

First, we need to create the print.sl file in the base folder so we can start writing the print operation. The print operation is as simple as they get. It just takes in a input and prints it out using Python.

Namespace

All CloudSlang files start with a namespace which mirrors the folder structure in which the files are found. In our case we’ve put print.sl in the tutorials/base folder so our namespace should reflect that.

namespace: tutorials.base

The namespace can be used by flows that call this operation.

For more information, see namespace in the DSL reference.

Operation Name

Each operation begins with the operation key which will map to the contents of the operation body. The first part of that body is a key:value pair defining the name of the operation. The name of the operation must be the same as the name of the file it is stored in.

operation:
  name: print

Note

YAML Note: Indentation is very important in YAML. It is used to indicate scope. In the example above, you can see that name: print is indented under the operation key to denote that it belongs to the operation. Always use an identical number of spaces to indent. Never use tabs. For more information, see the YAML Overview.

For more information, see operation in the DSL reference.

Inputs

After the name, if the operation takes any inputs, they are listed under the inputs key. In our case we’ll need to take in the text we want to print. We’ll name our input text.

inputs:
  - text

Note

YAML Note: The inputs key maps to a list of inputs. In YAML, a list is signified by prepending a hyphen (-) and a space to each item.

The values for the inputs are either passed via the CloudSlang CLI, as we do below in this lesson, or from a step in a flow, as we will do in the next lesson.

Inputs can also have related parameters, such as required, default, private and sensitive. We will discuss these parameters in lessons 8 - Input Parameters.

For more information, see inputs, required, default, private and sensitive in the DSL reference.

Action

Finally, we’ve reached the core of the operation, the action. There are two types of actions in CloudSlang, Python-based actions and Java-based actions.

We’ll start off by creating a Python action that simply prints the text that was input. To do so, we add python_action and script keys that map to the action contents.

python_action:
  script: print text

Note

CloudSlang uses the Jython implementation of Python 2.7. For information on Jython’s limitations, see the Jython FAQ.

Python scripts that need 3rd party packages may import them using the procedures described in lesson 14 - 3rd Party Python Packages.

For more information, see python_action in the DSL reference.

The usage of Java-based actions is beyond the scope of this tutorial. For more information, see the java_action in the DSL reference.

Run It

That’s it. Our operation is all ready. Our next step will be to create a flow that uses the operation we just wrote, but we can actually just run the operation as is.

To do so, save the operation file, fire up the CloudSlang CLI and enter the following at the prompt to run your operation:

run --f <folder path>/tutorials/base/print.sl --i text=Hi

You should see the input text printed out to the screen.

For more information, see Use the CLI in the DSL reference.

Download the Code

Lesson 2 - Complete code

Up Next

In the next lesson we’ll write a flow that will call the print operation.

New Code - Complete

print.sl

namespace: tutorials.base

operation:
  name: print

  inputs:
    - text

  python_action:
    script: print text