I think you can achieve this without need to use custom tasks in native MSBuild 4, but I haven't started playing with that yet, so can't comment.
However, as for native MSBuild 3.5 I don't think it's possible - in order to manipulate the dates you need to break out into code. You see, the ModifiedDate metadata is internally a string - and to do sensible manipulations you need to convert to a date.
I'm not sure what is in the Sdc tasks - I don't use them as I prefer the CommunityTasks, but even with those tasks I can't think of anything that would work.
Custom MSBuild tasks aren't that scary - and I recommend that every (sizeable) project should have a solution that is built before any other solution that outputs a DLL containing your custom msbuild tasks into a well know location (eg a "lib" folder at the root of your source).
If you can allow this as a solution then here is a task I just knocked up that achieves what you want:
using System;
using System.Linq;
using Microsoft.Build.Framework;
using Microsoft.Build.Utilities;
namespace Build.MsBuildTasks
{
public class FindFilesOlderThan : Task
{
[Required]
public ITaskItem[] Files { get; set; }
public int Months { get; set; }
public int Days { get; set; }
public int Years { get; set; }
[Output]
public ITaskItem[] MatchingFiles { get; set; }
public override bool Execute()
{
var olderThan = DateTime.UtcNow.AddYears(-Years).AddMonths(-Months).AddDays(-Days);
MatchingFiles = (from f in Files
where DateTime.Parse(f.GetMetadata("ModifiedTime")) < olderThan
select f).ToArray();
return true;
}
}
}
You would then use it like so:
<UsingTask AssemblyFile="$(MSBuildProjectDirectory)\..\lib\Build.MsBuildTasks.dll"
TaskName="Build.MsBuildTasks.FindFilesOlderThan" />
<Target Name="Purge">
<ItemGroup>
<FilesToConsider Include="f:\temp\AzurePackages\**\*.*" />
</ItemGroup>
<FindFilesOlderThan
Files="@(FilesToConsider)"
Months="6">
<Output
TaskParameter="MatchingFiles"
ItemName="FilesToPurge"/>
</FindFilesOlderThan>
<Message Text="FilesToPurge: @(FilesToPurge)" />
</Target>
Of course, YMMV