Running simple Open Policy Agent Playground example from CLI

user_284503 0
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It's not clear to me how to run the Simple Example from the Open Policy Agent Playground from the CLI.

play.rego

package play
default hello = false

hello {
    m := input.message
    m == "world"
}

input.json

{
    "message": "world"
}

I tried using:

opa eval -i input.json -d play.rego "data.play.hello"

But, I could not get this result

{
    "hello": true
}

Unfortunately, I got this: :(

{
  "result": [
    {
      "expressions": [
        {
          "value": true,
          "text": "data.play.hello",
          "location": {
            "row": 1,
            "col": 1
          }
        }
      ]
    }
  ]
}

I thought others might find it useful to understand how to run these example from the CLI, so I had to ask.

open-policy-agent command-line-interface
1 Answers

That's a great question! Unless "evaluate selection" is selected, the Rego Playground always evaluates the entire policy, i.e. all rules included. When you query a policy using opa eval you can either choose to do the same, or as you do in your example - query just a single rule for its value.

If you change the query from "data.play.hello" to just "data.play" it will evaluate the full policy just like the playground:

$ opa eval -i input.json -d play.rego "data.play"
{
  "result": [
    {
      "expressions": [
        {
          "value": {
            "hello": true
          },
          "text": "data.play",
          "location": {
            "row": 1,
            "col": 1
          }
        }
      ]
    }
  ]
}

If you only want to display the actual output without all the details around it, you could use one of the formatting options available for opa eval such as --format raw:

$ opa eval --format raw -i input.json -d play.rego "data.play"
{"hello":true}
user_118492430
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