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Constructing Tasks from Bash Scripts GoToimage

Run a Bash script from within a workflow.

Prerequisites​

Import covalent.

import covalent as ct

Procedure​

This example returns the product of two numbers from a function in bash. The possible uses for this technique are endless. In software deployment scenario, for example, you could run a Makefile or a build command on a remote backend machine.

  1. Define a Covalent Lepton object containing the Bash script you want to run.
task = ct.Lepton(
    language="bash",
    command="product=$(({num_1} * {num_2}))",
    argtypes=[
        (int, ct.Lepton.INPUT_OUTPUT),
        (int, ct.Lepton.INPUT_OUTPUT),
        (int, ct.Lepton.OUTPUT)
    ],
    named_outputs=["num_1", "num_2", "product"]
)
  1. Write a lattice to run the task, then dispatch it and print the result.
@ct.lattice
def bash_multiply_workflow(**kwargs) -> str:
    return task(**kwargs)

result = ct.dispatch_sync(bash_multiply_workflow)(num_1=7, num_2=8).result
print(result)
(7, 8, 56)

The output results from executing the command product=$((7 * 8)). The parameter values num_1 and num_2 is replaced during execution with the passed values 7 and 8. The product variable and operands are then returned as specified in named_outputs.

The named_outputs parameter tells Covalent the environment variables from which to read the script output. You must specify the corresponding types in argtypes when constructing the Lepton. In this example, the num_1, num_2, and product variables are all defined as integers.