How do you pass empty arguments in Cake v1? - cakebuild

Question

According to the upgrade document it is no longer possible to ./build.sh arg= as of v1.0. Indeed, that produces:
Error: Expected an option value.
However it also doesn't work with arg=''. I could leave it off and rely on the default value, but that's hard to do from my Azure DevOps pipelines, which read like - script: ./build.sh --arg='$(arg1)' where arg1 is a variable defined elsewhere.
The problem is that the variable arg1 in my DevOps pipeline is defined externally and may or may not be empty.
The best I can think of is passing in at least a space like ./build.sh --arg='$(arg) ' (note the space at the end) and always checking for string.IsNullOrWhiteSpace and always Trimming, but that seems very hacky.
Is there a cleaner solution to pass a possibly empty variable from the command line? If not how can I rewrite my Azure DevOps YML to not pass the argument if it is empty?

Answer 1

TL;DR; Use a (space) instead of = if the value can be empty/null.
./build.sh --arg '$(arg1)'
Cake v1.0 supports using a space between the --argumentName and the value as an alternative for the = sign. For example:
dotnet cake empty-args.cake --arg1 --arg2
dotnet cake empty-args.cake --arg1 valueA --arg2
dotnet cake empty-args.cake --arg1 --arg2 valueB
dotnet cake empty-args.cake --arg1 valueA --arg2 valueB
With a sample Cake script like the below, it will output the following:
var arg1 = Argument<string>("arg1", null);
var arg2 = Argument<string>("arg2", null);
Information("arg1: {0}", arg1);
Information("arg2: {0}", arg2);
dotnet cake empty-args.cake --arg1 --arg2
arg1: [NULL]
arg2: [NULL]
dotnet cake empty-args.cake --arg1 --arg2
arg1: [NULL]
arg2: [NULL]
dotnet cake empty-args.cake --arg1 valueA --arg2
arg1: valueA
arg2: [NULL]
dotnet cake empty-args.cake --arg1 --arg2 valueB
arg1: [NULL]
arg2: valueB
dotnet cake empty-args.cake --arg1 valueA --arg2 valueB
arg1: valueA
arg2: valueB

Answer 2

One key difference with Cake 1.0 is that it beyond keyvalue arguments (--key=value), supports flags (--flag), and multiple arguments with the same name (--key=value1 --key=value2). Which allows for much more flexibility than before.
As no example script provided, my example will be emptyarg.cake looking like below
var arg = Argument<string>("arg", null);
Information("Arg: {0}", arg ?? "NULL");
dotnet cake .\emptyarg.cake will output Arg: NULL
dotnet cake .\emptyarg.cake --arg will output Arg: NULL
dotnet cake .\emptyarg.cake --arg=" " will output Arg:
If you want to treat all the above examples as an argument missing, you could create a reusable helper method.
public string ArgumentNotNullOrWhiteSpace(string key)
{
var value = Argument<string>(key, null);
return string.IsNullOrWhiteSpace(value)
? null
: value;
}
var arg = ArgumentNotNullOrWhiteSpace("arg");
Information("Arg: {0}", arg ?? "NULL");
Then output of
dotnet cake .\emptyarg.cake
dotnet cake .\emptyarg.cake --arg
dotnet cake .\emptyarg.cake --arg=hh
dotnet cake .\emptyarg.cake --arg=" "
will be
Arg: NULL
Arg: NULL
Arg: hh
Arg: NULL
and you can use ?? operator if you want some default value i.e.
var arg = ArgumentNotNullOrWhiteSpace("arg") ?? "default" and the output will be
Arg: default
Arg: default
Arg: hh
Arg: default