Different ways to pass variables in MSBuild

I'm rather new to MS Build and have been reviewing many of the built in target fi开发者_运维问答les that ship with Visual Studio. I have seen variables passed a few different ways and am not quite sure of the differences between these:

$(...)
@(...)
%(...)

• $(...)is used to access Property value (More info on Property element)

  <PropertyGroup>
    <Configuration>Debug</Configuration>
  </PropertyGroup>
  
  <Message Text="Configuration = $(Configuration)"/>
  

• @(...) is used to access Item value (More info on Item element)

  <ItemGroup>
    <Reference Include="System.Data"/>
    <Reference Include="System.Web.*"/>
  </ItemGroup>
  
  <Message Text="References = @(Reference)"/>
  

• %(...) is used to acces Item Metadata value (More info on Item Metadata). It's also used to do batching.

  <ItemGroup>
    <Compile Include="Account\ChangePassword.aspx.cs">
      <DependentUpon>ChangePassword.aspx</DependentUpon>
      <SubType>ASPXCodeBehind</SubType>
    <Compile/>
  </ItemGroup>
  
  <Message Text="Element @(Compile) of subtype %(SubType) and depend of %(DependentUpon)"/>
  

Dollar - $(MyProp): Allows you to reference values specified within PropertyGroups.

At Sign - @(CodeFile): Allows you to reference lists of items specified within ItemGroups.

Percent - %(CodeFile.BatchNum): Allows you to reference batched ItemGroup values using metadata. This is a bit more complicated, so definitely review the documentation for more info.

Take a look at each link for more detailed info on how these are used. Good luck -- hope this helps!

A bit of extension on the % (item metadata), there is also the Well-known item metadata: https://learn.microsoft.com/en-us/visualstudio/msbuild/msbuild-well-known-item-metadata?view=vs-2017

E.g. ModifiedTime:

  <ItemGroup>
    <IntermediateAssembly Include="$(IntermediateOutputPath)$(TargetName)$(TargetExt)"/>
  </ItemGroup>

<PropertyGroup>
  <_AssemblyTimestampBeforeCompile>%(IntermediateAssembly.ModifiedTime)</_AssemblyTimestampBeforeCompile>
</PropertyGroup>