Jenkins Pipeline throws "syntax error: bad substitution" when Passing in Parameter - shell

Question

I have a Terraform project that I was trying to use Jenkin's Custom Checkbox plugin (Custom Checkbox Parameter) with so that I can build separate applications dynamically using the same IaC, however, I'm getting the following error when passing in the name parameter for that plugin into the Terraform plan and apply commands.
syntax error: bad substitution
The idea for all this is just to click on "select all" or each individual app and run the build, and this will create the IaC for the given application(s).
I have a terraform plan that I am running as a smoke test to verify the parameters above are being passed in correctly before running the apply. This looks like the following:
sh 'terraform plan -var-file="terraform-dev.tfvars" -var "app_name=[${params[${please-work}]}]" -input=false'
The documentation for the plugin states that you can reference the items checked by using this format: "${params['please-work']}" which is what I've done above. That said, one caveat to this is that Im having to set the values in quotes for this to work since the variables are being set in the Terraform using list(string).
NOTE: I have tested that all this works if I just hardcode the app names with the escapes as following:
sh 'terraform plan -var-file="terraform-dev.tfvars" -var "app_name=[\\"app-1\\",\\"app-2\\"]" -input=false'
Again, what I need is for this to work with the -var "app_name=[${params[${please-work}]}]" without throwing that error.
If needed, here is the setup for the JSON that the plugin is using:
Additionally, I can see the values are being set the way I need them to be set when running the echo of echo "${params['please-work']}" on the initial build step. So these are coming back as "app-1", "app-2"
Again, all but that one bit is working and I've tried various ways to escape the needed strings to get this work and I need insight on a path forward. This would be greatly appreciated.

Answer 1

You are casting the script argument in your sh step method as a literal string, and therefore it will not interpolate the pipeline variable of type object params within the Groovy pipeline interpreter. You also are passing the variable value for the app_name with [] syntax (attempted list constructor?), which is not syntactically valid for shell, Terraform, or JSON, but is for Jenkins Pipeline and Groovy with undesired behavior (unclear what is desired here). Finally, please-work is a literal string and not a Jenkins Pipeline or Groovy variable, and since params is technically an object and not a Map, you must use the . syntax and not the [] syntax for accessors. You must update with:
sh(label: 'Execute Terraform Plan', script: "terraform plan -var-file='terraform-dev.tfvars' -var 'app_name=${params.please-work}' -input=false")
If another issue arises after fixing all of this, then it would be recommended to convert the plugin usage to the pipeline with a parameters directive, and also to probably remove the unusual characters e.g. - from the parameter name.

Answer 2

Thanks for helping me think through this, Matt. I was able to resolve the issue with the following shell script in the declarative pipeline:
sh "terraform plan -var-file='terraform-dev.tfvars' -var 'app_name=[${params['please-work']}]' -input=false"
This is working now.