[SOLVED] Replace Indented text using SED

Issue

I am looking at replacing some indented lines in a Yaml file using sed.

      resources:
        limits:
          cpu: 500m
          memory: 512Mi
        requests:
          cpu: 250m
          memory: 256Mi

Yaml is strict about its indentation and will want to know how I can accomplish a replacement of the text after example "limits:"

I have tried '0,/cpu:.*m/s//cpu: 900m/' and '/limits:/!b;n;s//ccpu: 900m'

'0,/cpu:.*m/s//cpu: 900m/' outputs:

          resources:
        limits:
          cpu: 900m
          memory: 512Mi
        requests:
          cpu: 250m
          memory: 256Mi

The only issue I have with this is I will want to specify the replacement should be done on the example CPU for limits and not for the requests.

So I tried '/limits:/!b;n;s//ccpu: 900m' which outputs:

          resources:
        limits:
cpu: 900m
          memory: 512Mi
        requests:
          cpu: 250m
          memory: 256Mi

Notice how it is not properly indented? How can I achieve this by leaving the indentation as it is and also if I can specify 1st and 2nd lines after "limits:" or "requests:" that will be nice.

Solution

If you cannot install yaml parsing tools such as yq, you can use this gnu-sed solution:

sed -E '/limits:/!b;n;s/^([[:blank:]]*cpu: ).*/\1900m/' file.yml

      resources:
        limits:
          cpu: 900m
          memory: 512Mi
        requests:
          cpu: 250m
          memory: 256Mi

Breakdown:

• /limits:/!b: Search for text limits: otherwise branch to end of script
• n: Read/append the next line of input into the pattern space
• s/.../.../: Do this substitution
  • ^: Match start
  • ([[:blank:]]*cpu: ): Match 0 or more whitespaces followed by text cpu: . Capture this in capture group #1
  • .*: Match remaining text till end of line
  • /\1900m/: Replace with back-reference of capture group #1 i.e. \1 followed by new value 900m

Answered By - anubhava

Answer Checked By - Katrina (WPSolving Volunteer)