azure devops - How to set a release pipeline variable to null

Question

I have a .json config file in my application. Using the variables tab when managing the release in Azure DevOps, I can substitute values in that .json file. However, I am unable to explicitly set a value to null instead of string "null" using this method. Is there a way to do this? I need the resulting json to look like

"setting": null

instead of

"setting": "null"

question from:https://stackoverflow.com/questions/65942181/how-to-set-a-release-pipeline-variable-to-null

Answer 1

If you set the variable in Variables tab but don’t specify its value, its value is null.

However, when referring to this variable in scripts, it will be parsed to null string and is not null value.

For example, we have a test.json with below content.

    "setting": "debug",
    "environment": "dev"
}

If we use the command line task with below content.

echo Hello world

cat $(System.DefaultWorkingDirectory)/_tt/test.json

echo ""
echo "now replace: "

sed "s/"debug"/$testvar/g" $(System.DefaultWorkingDirectory)/_tt/test.json

The output result is below.

If you want to set it to null, just directly use null value with below content.

sed 's/"debug"/null/g' $(System.DefaultWorkingDirectory)/_tt/test.json

The output result is below.

And usesed 's/"debug"/null/g' $(System.DefaultWorkingDirectory)/_tt/test.json >$(System.DefaultWorkingDirectory)/_tt/new_test.json will write output to new_test.json file.

See: How to Use sed to Find and Replace String in Files for details.