Subprocess

The subprocess variable lets you execute shell commands from templates.

Name	Type	Default	Constraints	Description
`command`	string	—	—	Shell command to execute.
`cwd`	string	`None`	—	Working directory.
`env`	mapping	`None`	—	Environment variables.
`timeout`	float	`30.0`	Up to `300.0`	Timeout in seconds. A value that is not positive counts as omitted.

The run method returns a result object with three fields:

Field	Type	Description
`stdout`	string	Standard output (decoded as UTF-8).
`stderr`	string	Standard error (decoded as UTF-8).
`exit_code`	int	Process exit code.

{%- set result = subprocess.run('hostname', timeout=5.0) -%}
{{ result.stdout | trim }}

Limits

Commands run under fixed ceilings, so one template cannot stall the whole application or exhaust its memory:

Every call is bounded by a timeout — the requested one, 30 seconds when none is given, and 300 seconds at the most. A command that runs longer is terminated together with the processes it started.
Each output stream is captured up to 8 MiB. A command that writes more is terminated as well.

In both cases the event is not produced and the reason is written to the generator log.

Subprocess calls run synchronously and block event production. Use short timeouts to avoid stalling the pipeline.