Optional Named Capture group with suffix

Question

I have a specification of the command

RENAME_SECTION file::section [new_file::]new_section

file, section and new_section are mandatory, new_file is optional.

Than means that all next expressions will match:

RENAME_SECTION io.cfg::BUS1 io.cfg::BUS3
RENAME_SECTION io.cfg::BUS2       io_new.cfg::BUS2
RENAME_SECTION io.cfg::VID VID1

I try to get all provided parameters with Python re.search(pattern, config_line) using the pattern

(?P<command>RENAME_SECTION\s)\s*(?P<file>\S+)::(?P<section>.*)\s+(?P<target_file>\S*)[::]?(?P<target_section>.*)

This pattern match two first cases, but not the third one, the reason is absents of last ::.

How can I bundle :: with target_file named capture group?

Answer 1

You may try this regex with an optional match and anchors:

^(?P<command>RENAME_SECTION)\s+(?P<file>\S+?)::(?P<section>\S+)\s+(?:(?P<target_file>\S+?)::)?(?P<target_section>.+)$

RegEx Demo

(?:(?P<target_file>\S+?)::)? is an optional non-capturing group that makes matching target_file and trailing :: optional.