Using environment variables within strings (interpolation) to output JSON

[Skowronek]

Given a pipeline env variable $MYVAR, how would one write the pipeline script command to interpolate the env var within my pipeline YAML? Here is very basic example:

script:

  - echo '{"myvar":"$MYVAR"}' > ~/file.json

Right now, the $MYVAR is not getting interpolated. have tried ${MYVAR} as well. Haven't found a lot of examples unfortunately.

Thanks.

[Graham Gatus]

@Skowronek in your example, the MYVAR variable wasn't interpolated due to the single quotes - you need to swap this out for double quotes. Alternatively, you can also use a 'here' document. Below is an example showing the broken approach, and two working approaches; double quoting, and using a here document:

image: atlassian/default-image:2

pipelines:
  default:
    - step:
        script:
          # Broken due to single quotes, bash wont substitute $MYVAR.
          - echo '{"myvar":"$MYVAR"}' > file1.json
          - cat file1.json
          # Works - escaping with double quotes.
          - echo "{\"myvar\":\"$MYVAR\"}" > file2.json
          - cat file2.json
          # Works - using a here document, see http://tldp.org/LDP/abs/html/here-docs.html
          - >
            cat <<EOF > file3.json
             {"myvar":"${MYVAR}"}
            EOF
          - cat file3.json

[Graham Gatus]

I'd also recommend using the 'jq' tool (https://stedolan.github.io/jq/) when trying to generate json. You can use it with variable substitution to build up complex json strings, e.g

jq -n --arg varname "$MYVAR" '{"myvar": $varname }'