Parse key/value pairs from MSBuild property - msbuild

Question

Say I have a property like:
<MyProp>Foo=Bar;Hello=World</MyProp>
This seems like a reasonably common property pattern in MSBuild. How would I go about fetching the value "World"? In an ideal world this might look something like:
$(MyProp).(Hello)
Edit: To be clear, the property is not of my own creation, it is the output from another target that is out of my control, so I cannot change the way the property is declared.

Answer 1

<Project xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
<PropertyGroup>
<MyProp>Foo=Bar;Hello=World</MyProp>
</PropertyGroup>
<Target Name="Foo">
<CreateItem Include="MyProp" AdditionalMetadata="$(MyProp)">
<Output TaskParameter="Include" ItemName="MyProp" />
</CreateItem>
<Message Text="Foo %(MyProp.Foo)" />
<Message Text="Hello %(MyProp.Hello)" />
</Target>
</Project>

Answer 2

You have two routes to follow as far as I am concerned
Declare a Property Group just like the following:
<PropertyGroup>
<Foo>Bar</Foo>
<Hello>World</Hello>
</PropertyGroup>
and then use the following method to access your properties
<Target Name="DoSomething">
<Message Text="Print this : $(Foo)" />
</Target>
or you might want to take ItemGroup Element approach like the following
<ItemGroup>
<MySolutionFiles Include="..\mySolution.sln" />
</ItemGroup>
<Target Name="PrintItems">
<Message Text="My Files: #(MySolutionFiles)" />
</Target>
You can have the following as well
<ItemGroup>
<MyProp
Include="Foo;Hello" />
</ItemGroup>
<Target Name="PrintMyItems">
<Message Text="MyProp: #(MyProp)" />
</Target>
If there is no choice over the input then one possible solution is parsing the input into an array and then taking it from there like the following:
<PropertyGroup>
<MyProp>Foo=Bar;Hello=World</MyProp>
<Split>$(MyProp.Split(';'))</Split>
</PropertyGroup>
and then play with the array items like the following:
<Target Name="DoPrint">
<Message text="$(Split[0])" />
</Target>
Split[0] item contains your Foo=Bar which can be split into two more strings just like above. This should keep you going for now.

Answer 3

You don't need a property group, it's just nice to have default values in case the user doesn't pass them.
For each property you pass, the syntax to access that property is $(PropertyName).
So if you pass:
msbuild.exe /p:P1=V1 /p:P2=V2;P3=V3
You would use the property name $(P1), $(P2), $(P3).
More on MsBuild properties here.