Azure DevOps pipeline template - how to concatenate a parameter - templates

Question

All afternoon I have been trying to get my head around concatenating a parameter in an ADO template. The parameter is a source path and in the template a next folder level needs to be added. I would like to achieve this with a "simple" concatenation.
The simplified template takes the parameter and uses it to form the inputPath for a PowerShell script, like this:
parameters:
sourcePath: ''
steps:
- task: PowerShell#2
inputs:
filePath: 'PSRepo/Scripts/MyPsScript.ps1'
arguments: '-inputPath ''$(sourcePath)/NextFolder''
I have tried various ways to achieve this concatenation:
'$(sourcePath)/NextFolder'
see above
'$(variables.sourcePath)/NextFolder'
I know sourcePath is not a variable, but tried based on the fact that using a parameter in a task condition it apparently only works when referencing through variables
'${{ parameters.sourcePath }}/NextFolder'
And some other variations, all to no avail.
I also tried to introduce a variables section in the template, but that is not possible.
I have searched the internet for examples/documentation, but no direct answers and other issues seemed to hint to some solution, but were not working.
I will surely be very pleased if someone could help me out.
Thanx in advance.

Answer 1

We can add the variables in our temp yaml file and pass the sourcePath to the variable, then we can use it. Here is my demo script:
Main.yaml
resources:
repositories:
- repository: templates
type: git
name: Tech-Talk/template
trigger: none
variables:
- name: Test
value: TestGroup
pool:
# vmImage: windows-latest
vmImage: ubuntu-20.04
extends:
template: temp.yaml#templates
parameters:
agent_pool_name: ''
db_resource_path: $(System.DefaultWorkingDirectory)
# variable_group: ${{variables.Test}}
temp.yaml
parameters:
- name: db_resource_path
default: ""
# - name: 'variable_group'
# type: string
# default: 'default_variable_group'
- name: agent_pool_name
default: ""
stages:
- stage:
jobs:
- job: READ
displayName: Reading Parameters
variables:
- name: sourcePath
value: ${{parameters.db_resource_path}}
# - group: ${{parameters.variable_group}}
steps:
- script: |
echo sourcePath: ${{variables.sourcePath}}
- powershell: echo "$(sourcePath)"
Here, I just use the workingDirectory to as the test path. You can use the variables also.
Attach my build result:

Answer 2

Thanx, Yujun. In meantime did get it working. Apparently there must have been some typo that did block the script from executing right as the se solution looks like one of the options mentioned above.
parameters:
sourcePath: ''
steps:
- task: PowerShell#2
inputs:
filePath: 'PSRepo/Scripts/MyPsScript.ps1'
arguments: '-inputPath ''$(sourcePath)/NextFolder''