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I need to use the below JSON file as input and this file could contain multiple variable entries. I need to search var1 or var2 in environment variables and replace the value in the below JSON.

{
  "var1": "valueplaceholder",
  "var2": "valueplaceholder"
}

I tried the below command

cat input.json | sed "s/\"\([A-Z0-9_]*\)\":\s*\"\([A-Za-z0-9_]*\)\"/\"\1\": \"$\1\"/g"

but it creates output like

{
  "var1": "$var1",
  "var2": "$var2"
}

How can I get the value of variables? I.e. I need the value of $var1 instead of text $var1.

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1
  • You are re-inventing templating. Don't re-invent the wheel, look for existing tools that do what you want and use them (if only because you'll run into all the problems and caveats and gotchas that the existing tool ran into and fixed years ago). This looks relevant to json and templates: Jsonnet Commented Jul 8, 2021 at 9:06

1 Answer 1

Reset to default
2

Given

$ cat file.json
{ "var1": "valueplaceholder", "var2": "valueplaceholder", "var3": "valueplaceholder" }

then, borrowing the with_entries structure from How to swap key and value of an object using jq? and making use of jq's $ENV array:

$ export var1="foo" var2="bar"
$ jq 'with_entries( .value = $ENV[.key] )' file.json
{
  "var1": "foo",
  "var2": "bar",
  "var3": null
}

or if you want to set unmatched variables to the empty string or to retain the original values

$ jq 'with_entries( .value = ($ENV[.key] // "") )' file.json
{
  "var1": "foo",
  "var2": "bar",
  "var3": ""
}

or

$ jq 'with_entries( .value = ($ENV[.key] // .value) )' file.json
{
  "var1": "foo",
  "var2": "bar",
  "var3": "valueplaceholder"
}

or, if you want to delete the non-existing keys

$ jq 'with_entries( .value = ($ENV[.key] // empty) )' file.json
{
  "var1": "foo",
  "var2": "bar"
}
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