`dotnet run -e FOO=BAR` passes `@(RuntimeEnvironmentVariable)` by jonathanpeppers · Pull Request #52664 · dotnet/sdk

jonathanpeppers · 2026-01-23T21:29:01Z

Context: #52492

In investigating how to pass implement dotnet-watch for mobile, we found that we need to make use of:

dotnet run -e FOO=BAR

Where FOO=BAR is passed as an MSBuild item @(RuntimeEnvironmentVariable) to the build, DeployToDevice target, and ComputeRunArguments target:

<ItemGroup>
  <RuntimeEnvironmentVariable Include="FOO" Value="BAR" />
</ItemGroup>

This is straightforward for the in-process MSBuild target invocations, but for the build step, we need to generate a temporary .props file and import using $(CustomBeforeMicrosoftCommonProps).

You will have to opt into this behavior by setting <ProjectCapability Include="RuntimeEnvironmentVariableSupport" /> in your project. The iOS and Android workloads would automatically set this capability.

In the iOS & Android workloads, we would handle processing the @(RuntimeEnvironmentVariable) item to pass the environment variables to the device/emulator when deploying and running the app.

I added a test to verify environment variables are passed through correctly to all targets.

Context: #52492 In investigating how to pass implement `dotnet-watch` for mobile, we found that we need to make use of: dotnet run -e FOO=BAR Where `FOO=BAR` is passed as an MSBuild item `@(RuntimeEnvironmentVariable)` to the build, `DeployToDevice` target, and `ComputeRunArguments` target: <ItemGroup> <RuntimeEnvironmentVariable Include="FOO" Value="BAR" /> </ItemGroup> This is straightforward for the in-process MSBuild target invocations, but for the build step, we need to generate a temporary `.props` file and import using `$(CustomBeforeMicrosoftCommonProps)`. In the iOS & Android workloads, we would handle processing the `@(RuntimeEnvironmentVariable)` item to pass the environment variables to the device/emulator when deploying and running the app. I added a test to verify environment variables are passed through correctly to all targets.

Updated the props file path generation to use Path.GetFullPath, ensuring that MSBuild receives an absolute path for the generated props file. This improves reliability when referencing the file in build processes.

Replaces backslashes with the system's directory separator in intermediateOutputPath to ensure consistent path handling across platforms. This prevents issues when MSBuild returns paths with Windows-style separators on non-Windows systems.

documentation/specs/dotnet-run-for-maui.md

baronfel · 2026-02-02T19:29:44Z

src/Cli/dotnet/Commands/Run/EnvironmentVariablesToMSBuild.cs

+        // directly to ProjectInstance for in-process target invocations.
+        var additionalProperties = new ReadOnlyDictionary<string, string>(new Dictionary<string, string>
+        {
+            [Constants.CustomBeforeMicrosoftCommonProps] = propsFilePath


I'm a little worried about this negatively impacting existing build processes - but I don't really have a way to validate how widely used this is.

A quick search around github shows ~250 instances, but none really appear foundational and some are in unrelated tooling. I'd expect large 1P customers to have some kind of use of this though, because they use all of the weird extensiblity points. I suppose if MSbuild ever makes a first-class way of injecting Items we could move to that.

This was a spot I didn't like either, here is a GitHub search:

https://github.com/search?q=CustomBeforeMicrosoftCommonProps+language%3AXML&type=code&l=XML

We could introduce a new property?

I really wanted to avoid creating a temp .props file but saw no other way

I think this is fine to get in for the first revision and revisit. If we did a new property we'd need to add 'massaging' of that property into Items, and that can also be an error-prone activity due to weird user inputs.

Copilot

Pull request overview

This PR adds support for passing environment variables from dotnet run -e to MSBuild targets as @(RuntimeEnvironmentVariable) items. Projects opt in to this feature by declaring the RuntimeEnvironmentVariableSupport project capability.

Changes:

Environment variables from -e flags are converted to MSBuild items and passed to build, deploy, and ComputeRunArguments targets
Opt-in mechanism using project capabilities to avoid impacting projects that don't need this feature
Temporary .props file generation for out-of-process build steps

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
test/dotnet.Tests/CommandTests/Run/GivenDotnetRunSelectsDevice.cs	Added tests to verify environment variables are passed to targets when opted in, and not passed when opt-out
test/TestAssets/TestProjects/DotnetRunDevices/DotnetRunDevices.csproj	Test project updated to opt in to capability and log environment variables in targets for verification
src/Cli/dotnet/Commands/Run/RunCommandSelector.cs	Added properties to check opt-in capability and retrieve IntermediateOutputPath for props file creation
src/Cli/dotnet/Commands/Run/RunCommand.cs	Modified to pass environment variables to selector, create props file for build, and add items for in-process targets
src/Cli/dotnet/Commands/Run/EnvironmentVariablesToMSBuild.cs	New utility class for converting environment variables to MSBuild items and managing temporary props files
src/Cli/Microsoft.DotNet.Cli.Utils/Constants.cs	Added constants for RuntimeEnvironmentVariable items, ProjectCapability, and related properties
documentation/specs/dotnet-run-for-maui.md	Documentation explaining the opt-in mechanism and implementation details

test/dotnet.Tests/CommandTests/Run/GivenDotnetRunSelectsDevice.cs

src/Cli/dotnet/Commands/Run/EnvironmentVariablesToMSBuild.cs

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Add support for the '@(RuntimeEnvironmentVariable)' item group, which is set when using 'dotnet run' and passing environment variables using '-e|--environment NAME=VALUE' to 'dotnet run'. This required adding the 'RuntimeEnvironmentVariableSupport' capability to tell 'dotnet run' that we support this. References: * dotnet/android#10770 * dotnet/sdk#52664

Add support for the '@(RuntimeEnvironmentVariable)' item group, which is set when using 'dotnet run' and passing environment variables using '-e|--environment NAME=VALUE' to 'dotnet run'. This required adding the 'RuntimeEnvironmentVariableSupport' capability to tell 'dotnet run' that we support this. References: * dotnet/android#10770 * dotnet/sdk#52664 --------- Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Merge branch 'release/10.0.3xx' into dev/peppers/dotnet-run-env

d6264a8

This was referenced Jan 26, 2026

The Operation will be canceled. The next steps may not contain expected logs. dotnet/dnceng#3008

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[android-arm64] The Operation will be canceled. The next steps may not contain expected logs. dotnet/dnceng#6408

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jonathanpeppers added 3 commits January 27, 2026 11:04

Ensure full path for MSBuild props file

fcc45c3

Updated the props file path generation to use Path.GetFullPath, ensuring that MSBuild receives an absolute path for the generated props file. This improves reliability when referencing the file in build processes.

Make $(UseRuntimeEnvironmentVariableItems)=true opt-in

7fb51d2

Workaround dotnet/msbuild#12546

07f2dc5

build-analysis bot mentioned this pull request Jan 28, 2026

slow macOS - "##[error]The job running on agent Azure Pipelines 9 ran longer than the maximum time of 60 minutes." dotnet/dnceng#1883

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3 tasks

jonathanpeppers added 3 commits January 28, 2026 14:43

EnableDefaultEmbeddedResourceItems -> EnableDefaultItems

7cd0e6b

Merge branch 'release/10.0.3xx' into dev/peppers/dotnet-run-env

0871b65

build-analysis bot mentioned this pull request Jan 29, 2026

dotnet-watch tests failing #40006

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Merge branch 'release/10.0.3xx' into dev/peppers/dotnet-run-env

ffb4b83

jonathanpeppers marked this pull request as ready for review February 2, 2026 17:59

jonathanpeppers requested review from baronfel, Copilot and rolfbjarne and removed request for Copilot February 2, 2026 17:59

Copilot started reviewing on behalf of jonathanpeppers February 2, 2026 18:00 View session

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baronfel reviewed Feb 2, 2026

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<ProjectCapability Include="RuntimeEnvironmentVariableSupport" />

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Copilot AI review requested due to automatic review settings February 2, 2026 20:27

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test/dotnet.Tests/CommandTests/Run/GivenDotnetRunSelectsDevice.cs Outdated Show resolved Hide resolved

src/Cli/dotnet/Commands/Run/EnvironmentVariablesToMSBuild.cs Show resolved Hide resolved

jonathanpeppers and others added 2 commits February 2, 2026 16:59

Update test/dotnet.Tests/CommandTests/Run/GivenDotnetRunSelectsDevice.cs

007dd66

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Merge branch 'release/10.0.3xx' into dev/peppers/dotnet-run-env

b5972e0

jonathanpeppers requested a review from MiYanni February 3, 2026 16:56

MiYanni approved these changes Feb 3, 2026

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jonathanpeppers merged commit bd5d3af into release/10.0.3xx Feb 4, 2026
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jonathanpeppers deleted the dev/peppers/dotnet-run-env branch February 4, 2026 15:04

jonathanpeppers mentioned this pull request Feb 4, 2026

[Epic] vibe-coding .NET MAUI apps works out of the box dotnet/maui#32967

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dotnet-maestro bot mentioned this pull request Feb 12, 2026

[release/10.0.3xx] Source code updates from dotnet/sdk dotnet/dotnet#4826

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rolfbjarne mentioned this pull request Mar 4, 2026

[dotnet] Add support for @(RuntimeEnvironmentVariable). dotnet/macios#24824

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dotnet-maestro bot mentioned this pull request Mar 6, 2026

[main] Source code updates from dotnet/sdk dotnet/dotnet#5268

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`dotnet run -e FOO=BAR` passes `@(RuntimeEnvironmentVariable)`#52664

`dotnet run -e FOO=BAR` passes `@(RuntimeEnvironmentVariable)`#52664
jonathanpeppers merged 12 commits intorelease/10.0.3xxfrom
dev/peppers/dotnet-run-env

jonathanpeppers commented Jan 23, 2026 •

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jonathanpeppers commented Jan 23, 2026 •

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