Using runtime expressions in azure pipelines yaml script - azure-devops

Question

I'm trying to execute script by passing variable from the azure pipeline. Here is my simple test pipeline:
trigger:
- master
pool:
vmImage: 'windows-latest'
variables:
major: 1.2
minor: $[counter(variables['major'], 1)]
version: $[format('{0}.{1}', variables.major, variables.minor)]
name: $[format('{0} v{1}', 'Yaml Testing', variables['version'])]
steps:
- script: |
echo variables['version']
echo $(variables.version)
echo '$(variables.version)'
echo "$(variables.version')"
echo $[ variables['version'] ]
echo ${{ variables['version'] }}
echo $(Build.BuildNumber)
displayName: 'Run a multi-line script'
- script: $[format('{0} {1}', 'echo', variables['version'])]
displayName: 'Echo Formatted String'
Outputs of scripts are:
Generating script.
========================== Starting Command Output ===========================
##[command]"C:\windows\system32\cmd.exe" /D /E:ON /V:OFF /S /C "CALL "d:\a\_temp\3cb45b74-f6cd-4d2f-bf65-f635779b9d86.cmd""
variables['version']
$(variables.version)
'$(variables.version)'
"$(variables.version')"
$[ variables['version'] ]
$[format('{0}.{1}', variables.major, variables.minor)]
Yaml Testing v1.2.11
##[section]Finishing: Run a multi-line script
and
Generating script.
Script contents:
$[format('{0} {1}', 'echo', variables['version'])]
========================== Starting Command Output ===========================
##[command]"C:\windows\system32\cmd.exe" /D /E:ON /V:OFF /S /C "CALL "d:\a\_temp\5e42dc54-e027-4b9a-9af4-0db02e879b0f.cmd""
'$[format' is not recognized as an internal or external command,
operable program or batch file.
##[error]Cmd.exe exited with code '1'.
##[section]Finishing: Echo Formatted String
Strangely, code work fine in the name, but not when trying to use in the script.
What am I doing wrong?

Answer 1

$[] is evaluated at runtime, that is why it is not working. You can pass ${{expression}} to script like below:
- script: ${{format('{0} {1}', 'echo', '$(version)')}}
displayName: 'Echo Formatted String'
Expression in ${{}} will be evaluated at parse time. Before the -script is actually executed, expression in
${{}} is parsed into a valid command.
You can directly refer to the self-defined variables like this '$(variableName)' instead of $(variables.Name)