Execute shell commands as flows

This page explains how to use the watch and serve Prefect CLI commands to execute and schedule shell commands as Prefect flows, including how to:

• run a shell command as a Prefect flow on-demand with watch
• schedule a shell command as a recurring Prefect flow using serve

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Prerequisites

Before you begin, ensure you have:

• A basic understanding of Prefect flows. Start with the Getting started guide if necessary.
• A recent version of Prefect installed in your command line environment. Follow these instructions if you have any issues.

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The watch command

The watch command wraps any shell command in a Prefect flow for instant execution. This is ideal for quick tasks or integrating shell scripts into your workflows.

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Example usage

To fetch the current weather in Chicago using the curl command, use the following Prefect CLI command:

prefect shell watch "curl http://wttr.in/Chicago?format=3"

This command makes a request to wttr.in, a console-oriented weather service, and prints the weather conditions for Chicago.

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Benefits of watch

• Immediate feedback: Execute shell commands within the Prefect framework for immediate results.
• Easy integration: Blend external scripts or data fetching into your data workflows.
• Visibility and logging: Use Prefect’s logging to track the execution and output of your shell tasks.

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Deploy with serve

To run shell commands on a schedule, the serve command creates a Prefect deployment for regular execution. This is a quick way to create a deployment served by Prefect.

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Example usage

To set up a daily weather report for Chicago at 9 AM, use the serve command as follows:

prefect shell serve "curl http://wttr.in/Chicago?format=3" --flow-name "Daily Chicago Weather Report" --cron-schedule "0 9 * * *" --deployment-name "Chicago Weather"

This command schedules a Prefect flow to fetch Chicago’s weather conditions daily, providing consistent updates without manual intervention. To manually fetch the Chicago weather, create a run of your new deployment from the UI or CLI.

To shut down your server and pause your scheduled runs, hit ctrl + c in the CLI.

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Benefits of serve

• Automated scheduling: Schedule shell commands to run automatically, ensuring critical updates are generated and available on time.
• Centralized workflow management: Manage and monitor your scheduled shell commands inside Prefect for a unified workflow overview.
• Configurable execution: Customize execution frequency, concurrency limits, and other parameters to suit your project’s needs and resources.