C# REPL outside Visual Studio

Question

F# has a REPL (read–eval–print loop) F# Interactive, C:\Program Files (x86)\Microsoft F#\v4.0\Fsi.exe.

I understand C# now has its own interactive REPL, as released with Roslyn. How do I open outside Visual Studio? Where is csi.exe?

Answer 1

Best Option in 2023

The best option nowadays is using CSharpRepl. Action talks louder than words:

Install it using this command dotnet tool install -g csharprepl. And to use it run this command in terminal csharprepl
It has many features you can even install nuget packages or use your own code by referencing to the assembly of it. Documentation

Answer 2

If you're using dotnet core then try dotnet-script.

run dotnet tool install --global dotnet-script to install. Then run dotnet-script to get a REPL style command prompt

> Console.WriteLine("Hello world!");
Hello world!

Info found here

Answer 3

use powershell find csi.exe:

PS > Get-ChildItem "C:\Program Files (x86)\" -Recurse | Where-Object Name -CMatch "csi.exe"

below is my output:

    Directory: C:\Program Files (x86)\Microsoft Visual Studio\2017\Enterprise\MSBuild\15.0\Bin\Roslyn


Mode                LastWriteTime         Length Name                                                                                                                        
----                -------------         ------ ----                                                                                                                        
-a----        12/9/2018   6:42 PM          15712 csi.exe                                                                                                                     
-a----        12/9/2018   6:42 PM           8482 csi.exe.config                                                                                                              


    Directory: C:\Program Files (x86)\Microsoft Visual Studio\Shared\Packages\Microsoft.CodeDom.Providers.DotNetCompilerPlatform.2.0.0\tools\Roslyn45


Mode                LastWriteTime         Length Name                                                                                                                        
----                -------------         ------ ----                                                                                                                        
-a----        5/24/2018   1:38 PM          13680 csi.exe                                                                                                                     


    Directory: C:\Program Files (x86)\Microsoft Visual Studio\Shared\Packages\Microsoft.CodeDom.Providers.DotNetCompilerPlatform.2.0.0\tools\RoslynLatest


Mode                LastWriteTime         Length Name                                                                                                                        
----                -------------         ------ ----                                                                                                                        
-a----        5/24/2018   1:38 PM          15280 csi.exe                                                                                                                     
-a----        5/24/2018   1:38 PM           8816 csi.exe.config                                                                                                              


    Directory: C:\Program Files (x86)\Microsoft Visual Studio\Shared\Packages\Microsoft.Net.Compilers.1.3.2\tools


Mode                LastWriteTime         Length Name                                                                                                                        
----                -------------         ------ ----                                                                                                                        
-a----        6/27/2016   2:50 PM          13680 csi.exe                                                                                                                     


    Directory: C:\Program Files (x86)\Microsoft Visual Studio\Shared\Packages\Microsoft.Net.Compilers.2.0.1\tools


Mode                LastWriteTime         Length Name                                                                                                                        
----                -------------         ------ ----                                                                                                                        
-a----         3/7/2017  10:56 AM          14192 csi.exe                                                                                                                     
-a----         3/7/2017  10:56 AM           7905 csi.exe.config                                                                                                              


    Directory: C:\Program Files (x86)\Microsoft Visual Studio\Shared\Packages\Microsoft.Net.Compilers.2.1.0\tools


Mode                LastWriteTime         Length Name                                                                                                                        
----                -------------         ------ ----                                                                                                                        
-a----        4/13/2017   3:47 PM          14192 csi.exe                                                                                                                     
-a----        4/13/2017   3:47 PM           8006 csi.exe.config                                                                                                              


    Directory: C:\Program Files (x86)\Microsoft Visual Studio\Shared\Packages\Microsoft.Net.Compilers.2.4.0\tools


Mode                LastWriteTime         Length Name                                                                                                                        
----                -------------         ------ ----                                                                                                                        
-a----        9/21/2017  11:42 PM          15312 csi.exe                                                                                                                     
-a----        9/21/2017  11:42 PM           8816 csi.exe.config                                                                                                              


    Directory: C:\Program Files (x86)\Microsoft Visual Studio\Shared\Packages\Microsoft.Net.Compilers.2.6.1\tools


Mode                LastWriteTime         Length Name                                                                                                                        
----                -------------         ------ ----                                                                                                                        
-a----       12/13/2017  10:09 PM          16296 csi.exe                                                                                                                     
-a----       12/13/2017  10:09 PM           8816 csi.exe.config                                                                                                              

Answer 4

It may not be a substitute but I mainly use RoslynPad for quick research and test. I've also used Linqpad. RoslynPad is "A simple C# editor based on Roslyn" according to their website https://roslynpad.net/. You can write small scripts and you can see variables values' and you may also save them.

Answer 5

C# Interactive window and csi.exe REPL were added to Visual Studio 2015 Update 1 (emphasis mine):

Introducing Interactive

The Interactive Window is back! The C# Interactive Window returns in Visual Studio 2015 Update 1 along with a couple other interactive treats:

• C# Interactive. The C# Interactive window is essentially a read-eval-print-loop (REPL) that allows you to play and explore with .NET technologies while taking advantage of editor features like IntelliSense, syntax-coloring, etc. Learn more about how to use C# Interactive on Channel 9 or by reading our beginner’s walkthrough.

• csi. If you don’t want to open Visual Studio to play around with C# or run a script file, you can access the interactive engine from the Developer Command Prompt. Type csi /path/myScript.csx to execute a script file or type simply csi to drop inside the command-line REPL.

• Scripting APIs. The Scripting APIs give you the ability to execute snippets of C# code in a host-created execution environment. You can learn more about how to create your own C# script engine by checking out our code samples.

See What’s New in Visual Studio 2015 Update 1 for .NET Managed Languages.

---

https://www.visualstudio.com/en-us/news/vs2015-update1-vs.aspx

>csi
Microsoft (R) Visual C# Interactive Compiler version 1.1.0.51109
Copyright (C) Microsoft Corporation. All rights reserved.

Type "#help" for more information.
> #help
Keyboard shortcuts:
  Enter         If the current submission appears to be complete, evaluate it.  Otherwise, insert a new line.
  Escape        Clear the current submission.
  UpArrow       Replace the current submission with a previous submission.
  DownArrow     Replace the current submission with a subsequent submission (after having previously navigated backwards).
REPL commands:
  #help         Display help on available commands and key bindings.
Script directives:
  #r            Add a metadata reference to specified assembly and all its dependencies, e.g. #r "myLib.dll".
  #load         Load specified script file and execute it, e.g. #load "myScript.csx".
>
> Enumerable.Range(10)
(1,12): error CS7036: There is no argument given that corresponds to the required formal parameter 'count' of 'Enumerable.Range(int, int)'
> Enumerable.Range(1, 10)
RangeIterator { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 }

Answer 6

How about scriptcs: http://scriptcs.net/?

There is a REPL and you even get the power of NuGet.

Answer 7

The only executable I found is C:\Program Files (x86)\Microsoft Codename Roslyn CTP\Binaries\rcsi.exe, which can execute .csx files. But it doesn't seem to actually support REPL.

Answer 8

I created exactly what you are asking for, a Roslyn based REPL running outside VisualStudio.

You can download it from PoC - Roslyn C# ScriptEngine Execute v1.0.exe which is a stand-alone exe containing all Roslyn assemblies as embedded resources. See also Video: Using O2's Roslyn-based C# REPL Script environment

Note that I have developed a more powerful C# REPL for the O2 Platform, which you can see and download from C# REPL Script Environment

On the topic of Roslyn, here are a number of other stand-alone tools that I created:

• Util - View Roslyn AST Graph v1.0.exe - good to see the AST tree created by Roslyn
• Util - Exe Creator (using Roslyn Compiler v1.0.exe - Nice tool to create stand alone exes
• Util - Roslyn - Compile Solution and view errors v1.0.exe - compile entire solutions
• Util - Roslyn - OnSave Compile Solution (with REPL) v1.0.exe - adds a REPL for Roslyn objects
• PoC - Roslyn refactor on InitializerExpressions v1.0.exe - shows an refactoring example
• Util - Roslyn AST Refactoring via REPL Script v1.0.exe - gui to develop refactoring scripts
• Util - Roslyn Cat.Net- Compile and Scan Solution v1.0.exe - shows integration of code compile and security scanning (Cat.NET will be download the first time this tool is executed)

Note that all these tools and the O2 Platform are released under an Open Source license, so please fell free to expand and make them better :)

Answer 9

Anders Hejlsberg builds a C# REPL loop in this video, 65 minutes in:

http://channel9.msdn.com/Events/PDC/PDC08/TL16#time=65m00s

It's a much older version of Roslyn, but the same ideas apply (and eval! ;).