Based on the output to get value with regular expression

Question

There's an output like this:

RA#show segment-routing traffic-eng on-demand color detail | utility egrep Color -B 10
Sat Dec 25 11:24:22.891 JST

SR-TE On-Demand-Color database
------------------------

On-Demand Color: 20
--
 Performance-measurement:
   Reverse-path Label: Not Configured
   Delay-measurement: Disabled
   Liveness-detection: Enabled 《-------
     Profile: liveness1
     Invalidation Action: down
     Logging:
       Session State Change: Yes
 Per-flow Information:
  Default Forward Class: 0
On-Demand Color: 23
--
 Performance-measurement:
   Reverse-path Label: Not Configured
   Delay-measurement: Disabled
   Liveness-detection: Enabled  《--------
     Profile: liveness1
     Invalidation Action: down
     Logging:
       Session State Change: Yes
 Per-flow Information:
  Default Forward Class: 0
On-Demand Color: 301

regex "On-Demand Color:\s(\S+)" can be used to extract color "20,23,301", but as Liveness-detection was not enabled under "On-Demand Color: 301", So I expected only color "20" and "23" can be extacted. Is it possible to achieve this by regular expression?

user_1996066 · Answer

Yes, it is possible to do this with regex, although beware that a parser would probably be better in this scenario. The idea is to search for the string that you want as long as it has a "Liveness-detection: Enabled" afterwards.

The regex would look like this:

On-Demand Color:\s(\S+) .* .* .* .* .*Liveness-detection: Enabled

Demo: https://regex101.com/r/SElvt2/1

And basically it matches also a few lines after you find the "On-Demand Color:" string. This regex can further be simplified to this:

On-Demand Color:\s(\S+)( .*?)*Liveness-detection: Enabled

Demo: https://regex101.com/r/857JQM/1

So that the "Liveness-detection:" string can be a few lines before of after the expected position.

user_5424988 · Answer

If you want to be a bit more flexible and if the value can be present after n number of lines instead of exactly 5, you can make use of a negative lookahead.

This will also prevent overmatching if Liveness-detection: Enabled is not present in the current On-Demand Color: part.

On-Demand Color:\s(\S+)(?:
(?!On-Demand Color:|\s*Liveness-detection:).*)*
\s*Liveness-detection: Enabled

The pattern matches:

On-Demand Color: Match the starting string
\s(\S+) Match a whitespace char and capture 1+ non whitespace chars (or use (\d+)for digits) in capture group 1
(?: Non capture group
- (?!On-Demand Color:|\s*Liveness-detection:)
- .* Match the whole line
)* Close non capture group and optionally repeat
\s*Liveness-detection: Enabled Match a newline, optional whitespace chars and the string that you want to match

Regex demo

user_17758782 · Answer

For your 2nd method, this might be better.

On-Demand Color:\s(\S+)(?:
.*){5}Liveness-detection: Enabled

Based on the output to get value with regular expression

3 Answers