Command-Line Arguments

Arguments that you can pass to an engine executable to customize how the engine runs on startup.

In Unreal Engine, Command-line Arguments, also called Additional Launch Parameters, customize how the engine runs on startup. Similar to console commands, command-line arguments can be an invaluable tool for testing and optimizing your project. These settings range from high-level operations, such as forcing the Unreal Editor to run in game mode instead of full-editor mode, to more detailed options, such as choosing a specific map to run within your game at a particular resolution and framerate.

Pass Command-Line Arguments

There are three common methods to pass command-line arguments to your Unreal Engine project or executable. These methods correspond to different ways of running your project:

From the Command-Line

The general syntax for adding command-line arguments to an executable run from the command-line is: 

<EXECUTABLE> [URL_PARAMETERS] [ARGUMENTS]

where:

  • EXECUTABLE is the name of your executable file.

    • Examples: UnrealEditor.exe, MyGame.exe

  • URL_PARAMETERS are any optional URL parameters.

    • Examples: MyMap, /Game/Maps/BonusMaps/BonusMap.umap?game=MyGameMode

  • ARGUMENTS include additional, optional command-line flags or key-value pairs.

    • Examples: -log, -game, -windowed, -ResX=400 -ResY=620

For example, the following input runs the MyGame project on the BonusMap in the MyGameMode game mode fullscreen on Windows: 

UnrealEditor.exe MyGame.uproject /Game/Maps/BonusMaps/BonusMap.umap?game=MyGameMode -game -fullscreen

From the Editor

The Unreal Editor supports customizing standalone games with command-line arguments. In the Unreal Editor, command-line arguments are referred to as additional launch parameters. Additional launch parameters are only supported for the Play in Standalone Game mode. The Unreal Editor also supports command-line arguments passed specifically to a separate, dedicated server for testing multiplayer games. Command-line arguments for a separate server are passed in three different places within the Unreal Editor:

  • Server Map Name Override: this is where you can pass map name as a URL parameter.

  • Additional Server Game Options: this is where you can pass additional URL parameters.

  • Additional Server Launch Parameters: this is where you can pass any other additional command-line flags or key-value pairs.

Additional Launch Parameters

Customize additional launch parameters within the Unreal Editor in the Editor Preferences.

Game Arguments

To pass command-line arguments to a standalone game launched from within the Unreal Editor, follow these steps:

  1. Navigate to Edit > Editor Preferences. A new window pops up with a tab titled Editor Preferences.

  2. On the left-hand side, select Level Editor > Play.

  3. On the right-hand side, find the section titled Play in Standalone Game.

  4. In this section, there is a textbox for Additional Launch Parameters. Paste your command-line arguments here. These additional parameters are then passed to the standalone game as command-line arguments.

Server Arguments

If you have checked Launch Separate Server and disabled Run Under One Process, you can specify the Server Map Name Override, Additional Server Game Options, and Additional Server Launch Parameters. To pass command-line arguments to a server launched from within the Unreal Editor, follow these steps:

  1. Navigate to Edit > Editor Preferences. A new window pops up with a tab titled Editor Preferences.

  2. On the left-hand side, select Level Editor > Play.

  3. On the right-hand side, find the section titled Multiplayer Options.

  4. If you have not already done so, do the following from within this section:

    1. Enable Launch Separate Server.

    2. Disable Run Under One Process.

  5. Navigate to Multiplayer Options > Server.

  6. In this section, there are three text boxes where you can specify different types of command-line arguments for your dedicated server: Server Map Name Override, Additional Server Game Options, and Additional Server Launch Parameters.

    1. Use the Server Map Name Override textbox to pass a map name as a URL parameter.

    2. Use the Additional Server Game Options textbox to pass additional URL parameters.

    3. Use the Additional Server Launch Parameters textbox to pass any additional command-line arguments.

Additional server launch parameters are only available if you choose to Launch Separate Server and disable Run Under One Process. When Run Under One Process is disabled, your clients run slower because each client spawns a separate instance of the Unreal Editor.

From an Executable Shortcut

To pass command-line arguments to an executable shortcut, follow these steps:

  1. Create a shortcut to your executable.

  2. Right-click on the shortcut and select Properties.

  3. Under the Shortcut section, add your command-line arguments to the end of the Target field.

  4. When you run this shortcut, the command-line arguments are passed to the original executable that the shortcut points to.

Create Your Own Command-Line Arguments

Unreal Engine provides some helpful C++ functions for parsing the command-line. You can create your own command-line arguments by passing your desired flag or key-value pair to the command-line as you would any other command-line argument. To use command-line arguments that you have passed, you need to read them from the command-line within your code. If your project code does not read your custom command-line arguments and parse them, the arguments are ignored.

Flags

Flags are switches that turn a setting on or off by their presence on the command-line. For example: 

UnrealEditor.exe MyGame.uproject -game

In this example, the -game argument is a flag because its presence on the command-line tells the Unreal Editor executable that you want to run MyGame in the game mode.

Parse Flags

To parse a flag from the command-line, use the FParse::Param function.

For example, suppose that you want to pass a boolean flag, -myflag, to your executable through the command-line as: 

UnrealEditor.exe MyGame.uproject -myflag

You can check whether this flag is present with the following code in your project: 

bool bMyFlag = false;
if (FParse::Param(FCommandLine::Get(), TEXT("myflag")))
{
    bMyFlag = true;
}

If -myflag is present on the command-line, the value of bMyFlag is true. If -myflag is not present on the command-line, the value of bMyFlag is false.

Key-Value Pairs

Key-value pairs are settings switches that specify a particular value for a switch. In addition to the presence of the switch, a setting must be provided for the switch. For example, in the following example: 

UnrealEditor.exe MyGame.uproject -game -windowed -ResX=1080 -ResY=1920

The -ResX=1080 and -ResY=1920 arguments are key-value pairs because each switch must be accompanied by a setting. In particular, these key-value pairs instruct the Unreal Editor executable to run at a particular resolution.

Parse Key-Value Pairs

To parse a key-value pair, use the FParse::Value function.

For example, suppose that you want to pass a key-value pair `-mykey=42`to your executable through the command-line: 

UnrealEditor.exe MyGame.uproject -mykey=42

You can parse this key-value pair with the following code: 

int32 myKeyValue;
if (FParse::Value(FCommandLine::Get(), TEXT("mykey="), myKeyValue))
{
    // if the program enters this "if" statement, mykey was present on the command-line
    // myKeyValue now contains the value passed through the command-line
}

If -mykey=42 is present on the command-line, the value of myKeyValue is 42. If -mykey=42 is not present on the command-line, the value of myKeyValue is not set.

You can find more information about what functions are available to interact with the command-line in CommandLine.h located in Engine\Source\Runtime\Core\Public\Misc.

Customize Engine Configuration from the Command-Line

Engine configuration is normally set in engine configuration .ini files. You can also customize engine configuration from the command-line. See the Configuration Files documentation for more information.

Customize Console Commands from the Command-Line

Console commands are normally executed from the console in the Unreal Editor. You can also customize console commands from the command-line. See the Console Variables documentation for more information.

Command-Line Arguments Reference

URL Parameters

URL parameters force your game to load a specific map upon startup. URL parameters are optional, but if you do provide them, they must immediately follow the executable name or any mode flag if one is present.

URL parameters consist of two parts:

Map Name

A map name can refer to any map located within the Maps directory. You can optionally include the .umap file extension. To load a map not found in the Maps directory, you must use an absolute path or a path relative to the maps directory. In this case, the .umap file extension is required.

Server IP Address

You can use a server IP address as a URL parameter to connect a game client to a dedicated server.

Additional Parameters

You can specify additional parameter options by appending them to the map name or the server IP address. Each option is prefaced by a ? (question mark) and set with = (equality or assignment). Prepending an option with - (dash) removes that option from the cached URL options.

Examples

Open Game with Map Located in Maps Directory
MyGame.exe MyMap
Open Game with Map Located Outside Maps Directory
MyGame.exe /Game/Maps/BonusMaps/BonusMap.umap
Open Game in Unreal Editor with Map Located Outside Maps Directory
UnrealEditor.exe MyGame.uproject /Game/Maps/BonusMaps/BonusMap.umap?game=MyGameMode -game
Connect a Game Client to a Dedicated Server

Supposing that you have a project, MyGame, that you want to run a server with the map BonusMap.umap located in /Game/Maps/BonusMaps/

You can run your dedicated server and connect your client locally as: 

UnrealEditor.exe MyGame.uproject /Game/Maps/BonusMaps/BonusMap.umap -server -port=7777 -log
UnrealEditor.exe MyGame.uproject 127.0.0.1:7777 -game -log

The arguments in this example are:

  • Server

    • MyGame.uproject: Run the MyGame project.

    • /Game/Maps/BonusMaps/BonusMap.umap: Open the BonusMap in your game. This is a URL parameter.

    • -server: Run the editor as a dedicated server.

    • -port=7777: Use port 7777 to listen for client connections. This is the default port for servers in Unreal Engine.

    • -log: Display the server log so that you can monitor server activity.

  • Game Client

    • MyGame.uproject: Run the MyGame project.

    • 127.0.0.1:7777: Connect to IP address 127.0.0.1 on port 7777. This is a server IP address.

    • -game: Run the editor as a game client.

    • -log: Display the game client log so that you can monitor client activity.

Flags and Key-Value Pairs

This section provides a reference of useful command-line arguments available to use when running Unreal Engine using any of the methods outlined in the section about how to pass command-line arguments.

Read Command-Line Arguments from a File

You might need to use a very large number of command-line arguments or need to reuse the same set of arguments often. You can store your command-line arguments in a text file and pass this file in the command-line for convenience. This is also useful if you find yourself hitting the Windows command-line length limit during testing.

The syntax for passing a text file containing command-line arguments is: 

<EXECUTABLE> -CmdLineFile=ABSOLUTE\PATH\TO\FILE.txt
Example

If you have a file named MyCmdLineArgs.txt saved in the directory D:\UnrealEngine and you want to pass it to the UnrealEditor.exe, you can do so with the following command: 

UnrealEditor.exe -CmdLineFile=D:\UnrealEngine\MyCmdLineArgs.txt

Useful Command-Line Arguments

General

Name

Flag or Key-Value Pair

Description

-log

Flag

Display a log window while the client or server is running.

-game

Flag

Mode flag to launch game client.

-server

Flag

Mode flag to launch dedicated server.

-newconsole

Flag

Wraps the server log in a window with access to a console to run console commands for your dedicated server.

-notimeouts

Flag

Use on the client target line to prevent clients from timing out while trying to connect to a server.

-windowed

Flag

Launch the client in windowed mode. Use in conjunction with -ResX=<HORIZONTAL_RES> -ResY=<VERTICAL_RES>.

-fullscreen

Flag

Launch the client in full-screen mode.

-ResX=<HORIZONTAL_RES> -ResY=<VERTICAL_RES>

Key-Value Pair

Specify the horizontal (X) and vertical (Y) resolution size for a client. Example: -ResX=1920 -ResY=1080
Rendering & GPU

Name

Flag or Key-Value Pair

Description

-d3d11

Flag

Run the editor in the DirectX 11 RHI.

-d3d12

Flag

Run the editor in the DirectX 12 RHI.

-vulkan

Flag

Run the editor in the Vulkan RHI.

-D3Ddebug

Flag

A debug layer for exposing hidden issues and verbose logging in the DirectX RHI.

-VulkanDebug

Flag

A debug layer for exposing hidden issues and verbose logging in the Vulkan RHI.

-gpuCrashDebugging

Flag

Enable Aftermath logging for NVIDIA GPUs on DirectX 12 or enable an equivalent logging in Vulkan for both AMD and NVIDIA.

-rhiValidation

Flag

A debug layer that sits above the RHI layer to catch low level RHI issues. Works on all platforms, not available in Test and Shipping build configurations.

-DumpGPU

Flag

Dump all of the current frame's internal resources to disk in a format that allows it to be inspected for debugging. This should be done every time a rendering crash is encountered.

-gpuValidation

Flag

For DirectX 12 and Vulkan. Adds instrumentation to the shader code to provide more information on hangs through additional validation on the GPU.

-ForceRHIBypass

Flag

Use in conjunction with -NoRHIThread. RHI calls are run inline with the renderer instead of queued for later execution.

-NoRHIThread

Flag

Use in conjunction with ForceRHIBypass. Runs with RHI calls being executed on the rendering thread instead of queued into a separate RHI thread.

-noshaderworker

Flag

Run the editor without distributed shader compilation. Each shader gets compiled one at a time in order to isolate issues with a single shader. This causes significant slowdowns at runtime.

-ddc=NoShared

Key-Value Pair

Run the editor without utilizing the compiled binary information in Derived Data Cache (DDC). This includes any information cached on the network DDC, cached animations, materials, textures, material functions, etc.

-ddc=cold

Key-Value Pair

Same as -ddc=NoShared except local DDC is also ignored. Useful for testing to diagnose or rule out DDC issues.

-logcmds="LogDerivedDataCacheVerbose"

Key-Value Pair

Provides more verbose DDC logging.
CPU & Memory

Name

Flag or Key-Value Pair

Description

-StompMAlloc

Flag

Check to ensure that incoming memory allocations do not overwrite memory addresses that are already in use.
Debugging

Name

Flag or Key-Value Pair

Description

-DebugCoreRedirects

Flag

Add additional information to UE logs to help identify core redirect issues.
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