Using MSBuild, how to expand wildcard files as one single line - msbuild

Question

Using MSBuild, after building an exe, I want to run it with a list of files coming from a wildcard expression.
I currently use something like this:
<Target Name="AfterBuild">
<ItemGroup>
<SigFiles Include="$(RootDir)tables\*.xml"/>
</ItemGroup>
<Exec Command="$(OutDir)app.exe --merge %(SigFiles.FullPath) -o $(OutDir)model.xml"/>
</Target>
The problem is that the command is executed once per file, using one file per command. With 3 .xml files, for instance, the following commands are run (paths omitted):
app.exe --merge a.xml -o model.xml
app.exe --merge b.xml -o model.xml
app.exe --merge c.xml -o model.xml
While I would like to run one single command with all files, blank separated:
app.exe --merge a.xml b.xml c.xml -o model.xml
How could I achieve this? No need to mention that I am not an MSBuild expert.
Thanks

Answer 1

When the '%' is used as you have it, a feature of MSBuild known as 'batching' is invoked. As you noted, the task is run multiple times, once for each item of the batch.
To reference the whole collection use '#'. The default delimiter between items is the semi-colon (;).
As an example, the following will display something like
a.xml;b.xml;c.xml
<Message Text="#(SigFiles)" />
A different delimiter can be specified. The following example uses a space.
<Message Text="#(SigFiles, ' ')" />
An item can also be 'transformed'. Your code is using FullPath. The following is not batching. The '%' is part of the transform expression.
<Message Text="#(SigFiles->'%(FullPath)')" />
Putting the transform and the delimiter together:
<Message Text="#(SigFiles->'%(FullPath)', ' ')" />
Taking the syntax we have built up and applying it to your original code:
<Exec Command="$(OutDir)app.exe --merge #(SigFiles->'%(FullPath)', ' ') -o $(OutDir)model.xml"/>