How do you use stdout?

[cpburnz]

How do you access stdout from a shell command? In Ansible, I'd just register the result of the shell command, and in the next action reference stdout from the result variable.

When I try this:

result = server.shell(commands="/usr/local/bin/node_exporter --version")

installed_version = re.search('version ([\\d.]+)', result.stdout_lines[0]).group(1)
if installed_version != EXPECTED_VERSION:
    # Install updated version.

I get the exception for "result.stdout_lines":

RuntimeError: Cannot evaluate operation result before execution

Which I understand to mean result.stdout_lines cannot be used directly outside of some execution context because pyinfra runs a simulation before actually executing the commands. So my question is how do I access stdout in an execution? I want to run more pyinfra operations depending on stdout.

[Fizzadar]

Hi @cpburnz - to access output during execution you’ll need to use a callback function: https://docs.pyinfra.com/en/next/using-operations.html#output-callbacks, has an example of it.