Passing regular expression from variable in jq

Question

I'm trying to filter AWS ECR image list returned as JSON with jq and regular expressions.

Following command work as expected and return filtered list:

aws ecr list-images --registry-id 123456789012 --repository-name repo | jq '.imageIds | map(select(.imageTag)) | map(select(.imageTag | test("[a-z0-9]-[0-9]")))'

[
  {
    "imageTag": "bbe3d9-2",
    "imageDigest": "sha256:4c0e92098010fd26e07962eb6e9c7d23315bd8f53885a0651d06c2e2e051317d"
  },
  {
    "imageTag": "3c840a-1",
    "imageDigest": "sha256:9d05e04ccd18f2795121118bf0407b0636b9567c022908550c54e3c77534f8c1"
  },
  {
    "imageTag": "1c0d05-141",
    "imageDigest": "sha256:a62faabb9199bfc449f0e0a6d3cdc9be57b688a0890f43684d6d89abcf909ada"
  }
]

But when I try to pass regular expression as an argument to jq it return an empty array.

aws ecr list-images --registry-id 123456789012 --repository-name repo | jq --arg reg_exp "[a-z0-9]-[0-9]" '.imageIds | map(select(.imageTag)) | map(select(.imageTag | test("$reg_exp")))'

[]

I have tried multiple ways to pass that variable, but just can't get it work. Other relevant information may be that I'm using zsh on mac and my jq version is jq-1.5. Any help is appreciated.

Answer 1

$reg_exp is a variable referring to your regular expression, "$reg_exp" is just a literal string. Remove the quotes. (and that extra map/select is redundant)

jq --arg reg_exp "[a-z0-9]-[0-9]" '.imageIds | map(select(.imageTag | test($reg_exp)))'