Sed replace regular expression by capture group match

user_425964 0
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I am attempting to use sed to replace a regular expression capture group. I've read that this requires enabling extended regular expressions with the -E flag. However, the following command is still not updating the text as expected.

echo "master-abcdef" | sed -i '' -E "s/IMAGE_TAG:\s*(\S+)$/\1/g" values.yaml

Where values.yaml has contents of:

global:
  env: default

default:
  IMAGE_TAG: dev-0be3323.zgm9a
  ... (more text below)

I am expecting values.yaml to be replaced to:

global:
  env: default

default:
  IMAGE_TAG: master-abcdef
  ... (more text below)
sed regex
3 Answers

You may use this in any version sed:

sed -i.bak -E 's/(IMAGE_TAG:[[:blank:]]+)[^[:blank:]]+/\1master-abcdef/' file.yml

cat file.yml

global:
  env: default

default:
  IMAGE_TAG: master-abcdef
  ... (more text below)

Here [[:blank:]] matches a space or tab.

If you are using gnu-sed then use:

sed -i -E 's/(IMAGE_TAG:\s+)\S+/\1master-abcdef/' file.yml
user_5482250

With yq, you can write

yq eval '.default.IMAGE_TAG = "master-abcdef"' values.yaml
user_75520

You can use

repl="master-abcdef"
sed -i '' -E "s/(IMAGE_TAG:[[:space:]]*).*/\\1$repl/" values.yaml

Here,

  • (IMAGE_TAG:[[:space:]]*) - captures into \1 an IMAGE_TAG: string and then any zero or more whitespaces
  • .* - matches the rest of the string (here, line).

The \1$repl replacement puts the captured value + the repl value in place of the matched text.

user_38329700
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