MSBuild: How to get the relative path to a file, given an absolute one?

Question

I have a situation where I have a bunch of absolute paths, and I would like to convert them to relative paths based on another directory with MSBuild. Here is the code I have so far:

<PropertyGroup>
    <FromPath>$(Bar)</FromPath>
</PropertyGroup>
<ItemGroup>
    <AbsolutePaths Include="@(Foo)" Exclude="@(Baz)" />
    <PathsRelativeToBar Include="@(AbsolutePaths->'???')" /> <!-- What goes here? -->
</ItemGroup>

Any help would be appreciated, thanks!

edit: I found a C#-based solution in this StackOverflow question, but I'm not sure how (or if it's possible) to convert it to MSBuild.

If you have the absolute path and relative working directory path, this could help : http://stackoverflow.com/questions/703281/getting-path-relative-to-the-current-working-directory — mojorisinify, Feb 18 '16 at 03:06
@mojorisinify Thanks for helping! I had seen that solution already. Unfortunately, I'm not really sure how I would translate that to MSBuild code. — James Ko, Feb 18 '16 at 03:47

duncanc · Accepted Answer · 2016-02-18T12:15:58.437

There is a native function in MSBuild called "MakeRelative"

Here is how you can use it.

<Project xmlns="http://schemas.microsoft.com/developer/msbuild/2003" DefaultTargets="Build" ToolsVersion="4.5" >
    <PropertyGroup>
        <Bar>c:\temp\msbuild-sample\2</Bar>
        <FromPath>$(Bar)</FromPath>
    </PropertyGroup>
    <ItemGroup>
        <AbsolutePaths Include="c:\temp\msbuild-sample\1\**\*.txt" />
    </ItemGroup>
    <Target Name="Build">
        <ItemGroup>
            <PathsRelativeToBar Include="@(AbsolutePaths)">
                <!-- Here is the magic... we're adding a piece of metadata with the relative path -->
                <RelativePath>$([MSBuild]::MakeRelative($(FromPath), %(AbsolutePaths.FullPath)))</RelativePath>
            </PathsRelativeToBar>
        </ItemGroup>
        <Message Text="----- Absolute paths -----" />
        <Message Text="%(AbsolutePaths.FullPath)" />
        <Message Text="----- Relative paths (showing full path) -----" />
        <Message Text="%(PathsRelativeToBar.FullPath)" />
        <Message Text="----- Relative paths (relative to $(FromPath)) -----" />
        <Message Text="%(PathsRelativeToBar.RelativePath)" />
    </Target>
</Project>

Here is a quick view of my current environment

C:\temp\msbuild-sample>dir /s /b

C:\temp\msbuild-sample\1
C:\temp\msbuild-sample\sample.build
C:\temp\msbuild-sample\1\1.1
C:\temp\msbuild-sample\1\1.txt
C:\temp\msbuild-sample\1\2.txt
C:\temp\msbuild-sample\1\1.1\3.txt
C:\temp\msbuild-sample\1\1.1\4.txt

and here is the output.

----- Absolute paths -----
c:\temp\msbuild-sample\1\1.1\3.txt
c:\temp\msbuild-sample\1\1.1\4.txt
c:\temp\msbuild-sample\1\1.txt
c:\temp\msbuild-sample\1\2.txt
----- Relative paths (showing full path) -----
c:\temp\msbuild-sample\1\1.1\3.txt
c:\temp\msbuild-sample\1\1.1\4.txt
c:\temp\msbuild-sample\1\1.txt
c:\temp\msbuild-sample\1\2.txt
----- Relative paths (relative to c:\temp\msbuild-sample\2) -----
..\1\1.1\3.txt
..\1\1.1\4.txt
..\1\1.txt
..\1\2.txt

Hope this helps :)

Awesome, very helpful answer! I never knew about that function. — James Ko, Feb 18 '16 at 16:02

MSBuild: How to get the relative path to a file, given an absolute one?

1 Answers1