Question

I need to parse a configuration file which looks like this (simplified):

<config>
<links>
<link name="Link1" id="1">
 <encapsulation>
  <mode>ipsec</mode>
 </encapsulation>
</link>
<link name="Link2" id="2">
 <encapsulation>
  <mode>udp</mode>
 </encapsulation>
</link>
</links>

My goal is to be able to change parameters specific to a particular link, but I’m having trouble getting substitution to work correctly. I have a regex that can isolate a parameter value on a specific link, where the value is contained in capture group 1:

link_id = r'id="1"'
parameter = 'mode'
link_regex = '<link [\w\W]+ %s>[\w\W]*[\w\W]*<%s>([\w\W]*)</%s>[\w\W]*</link>' \
% (link_id, parameter, parameter)

Thus,

print re.search(final_regex, f_read).group(1)

prints
ipsec

The examples in the regex howto all seem to assume that one wants to use the capture group in the replacement, but what I need to do is replace the capture group itself (e.g. change the Link1 mode from ipsec to udp).

Answer 1

not sure i’d do it that way, but the quickest way would be to shift the captures:

([\w\W][\w\W]<%s>)[\w\W]([\w\W])’ and replace with group1 +mode+group2