String partition

Extract output between two markers with partition()

Marker strings isolate command output when the response also contains logs, templates, warnings, or unrelated application content.

The command writes a unique marker before and after its output:

start_marker = "COMMAND_OUTPUT_START"
end_marker = "COMMAND_OUTPUT_END"

wrapped_command = f"echo {start_marker}; {command}; echo {end_marker}"

partition() splits a string at the first occurrence of the separator and returns three values: the text before it, the separator that was found, and the text after it. Applying it twice isolates the text between both markers.

def parse_output(response_text):
    before_output, start_found, after_start = response_text.partition(start_marker)
    command_output, end_found, after_output = after_start.partition(end_marker)
    parsed_output = command_output.strip()
    return parsed_output

Response body this parses

application content
COMMAND_OUTPUT_START
uid=33(www-data) gid=33(www-data)
COMMAND_OUTPUT_END
remaining application content

Returned value

uid=33(www-data) gid=33(www-data)

start_found and end_found contain the matching marker when it exists, or an empty string when it does not. before_output and after_output retain the discarded response content.

_{Find by: partition, string partition, split at marker, start marker, end marker, extract between markers, command output, noisy response, in band output, response parsing}