dot want to point at document root node absolutely

[wangrongjun]

I have a yaml as below, and I want to do a pre-handle, replace ${xxx} to actual value, which from yaml itself.

es-host: 192.168.1.101
gerrit-host: 192.168.1.102
deploy-info:
  es:
    server: ${es-host}:9200
  gerrit:
    server: ${gerrit-host}:8080

So, I replace by sub and eval:

yq -i '(.. | select(tag=="!!str")) |= (. | sub("\$\{(.+?)\}", eval(".$1")))' test.yaml

I expected:

es-host: 192.168.1.101
gerrit-host: 192.168.1.102
deploy-info:
  es:
    server: 192.168.1.101:9200
  gerrit:
    server: 192.168.1.102:8080

But actually is:

es-host: 192.168.1.101
gerrit-host: 192.168.1.102
deploy-info:
  es:
    server: :9200
  gerrit:
    server: :8080

You see, the eval can't get expected value, it just null. Because dot point at current node position after select, no longer point at document root position, and .deploy-info.es.server.es-host not exist, so eval return null.

Is there any way or a sign, can point at document root node absolutely?
Such as !, if I use eval("!.es-host"), it will find by document root absolutely, not relatively.
Thanks.

[mikefarah]

This was more complicated than I though. The short answer to your question is that you can use a create a variable to reference the root . as $r - however this by itself it not enough - because the sub command can only take a string to substitute to, not an expression. In the end I used 'capture' to grab the variable name like so:

yq '. as $r | "\$\{(?P<x>.+?)\}(?P<b>.*)" as $reg | 
with(.. | select(tag=="!!str" and match($reg)) ; 
capture($reg) as $c | . = ($r | eval("." + $c.x) + $b))

Explanation:

• . as $r will capture the root into the $r variable
• Because I need to use the reg ex twice, I saved that into a $reg variable as well
• "\$\{(?P<x>.+?)\}(?P<b>.*)" will capture the variable into 'x' and the rest of the string into 'b'
• with(.. | select(tag=="!!str" and match($reg)) ; will loop over all the strings that match that regex in the document
• capture($reg) as $c will run the reg ex with the capture groups, and put the result into the variable c
• Finally . = ($r | eval("." + $c.x) + $b will update the current string . by running the variable x from the capture group against the root $r | eval("." + $c.x) and the appending the remaining original string b.
• Phew.

Edit: formatting, and link to docs: https://mikefarah.gitbook.io/yq/operators/string-operators#capture-named-groups-into-a-map

[jmdesprez]

Hello,
Thanks for the answer.
I spotted a small typo, $b should be $c.b 🙂