ECA Editor — Unreal Editor Control via CmdLink

Execute ECA commands against a running Unreal Editor through the CmdLink named pipe.

Prerequisites

• Unreal Editor running with -cmdlink flag
• CmdLink.exe built from your engine (located at Engine/Binaries/Win64/CmdLink.exe)

Decision Flow — What to Use

Task requires controlling UE Editor
  |
  +-- Do you know which predefined command to use?
  |     +-- Yes --> ECA.Exec <command> '<json>'          <-- vast majority of cases
  |     +-- Not sure --> ECA.List [Category] to look up, then Exec
  |
  +-- No predefined command covers this operation?
  |     +-- describe_object to explore the target class
  |     +-- describe_function to confirm the signature
  |     +-- call_function to invoke it                   <-- escape hatch, not the normal path
  |
  +-- Need to run multiple commands in sequence?
        +-- ECA.Batch to send them all at once           <-- latency optimization, optional

Core principle: Predefined commands first. Reflection only when predefined commands don't cover the use case.

Calling Convention

# Set this to your engine's CmdLink.exe path
CMDLINK="<engine_root>/Engine/Binaries/Win64/CmdLink.exe"

# 1. Execute a command (most common)
$CMDLINK ECA.Exec <command_name> '<json_params>'

# 2. Discover commands (when unsure which to use)
$CMDLINK ECA.List              # List all categories
$CMDLINK ECA.List Actor        # List all commands + params in the Actor category

# 3. Batch (optional optimization for multiple sequential commands)
$CMDLINK ECA.Batch '[{"command":"cmd1","params":{...}},{"command":"cmd2","params":{...}}]'

Response Format

{"success":true,"result":{...}}

On error, the response includes the command's full parameter signature for self-correction:

{"success":false,"error":"...","expected":{"name":"create_actor","params":[{"name":"actor_type","type":"string","required":true}]}}

Batch response:

{"success":true,"count":2,"results":[{"command":"cmd1","success":true,"result":{...}},{"command":"cmd2","success":true,"result":{...}}]}

Common Examples

$CMDLINK ECA.Exec get_level_info '{}'
$CMDLINK ECA.Exec create_actor '{"actor_type":"PointLight","location":{"x":0,"y":0,"z":200}}'
$CMDLINK ECA.Exec take_gameplay_screenshot '{}'
$CMDLINK ECA.Exec find_actors '{"class_name":"StaticMeshActor"}'
$CMDLINK ECA.Exec lisp_to_blueprint '{"blueprint_path":"/Game/BP/BP_Test","code":"(event BeginPlay (call PrintString \"Hello\"))","clear_existing":true}'
$CMDLINK ECA.Exec save_all_dirty '{}'

Reflection Commands (only when predefined commands are insufficient)

# Explore: what functions and properties does this class have?
$CMDLINK ECA.Exec describe_object '{"object_path":"/Script/Engine.Actor","function_filter":"Location"}'

# Confirm signature: how do I call this function?
$CMDLINK ECA.Exec describe_function '{"object_path":"/Script/Engine.Actor","function_name":"GetActorLocation"}'

# Read property value (supports bVisible/Visible flexible lookup)
$CMDLINK ECA.Exec describe_property '{"object_path":"/Game/Maps/L.L:PersistentLevel.MyActor","property_name":"Visible"}'

# Find live instances
$CMDLINK ECA.Exec find_instances '{"class_name":"PointLight","limit":5}'

# Call any UFunction via reflection
$CMDLINK ECA.Exec call_function '{"object_path":"/Script/Engine.Default__KismetSystemLibrary","function_name":"PrintString","args":{"InString":"Hello"}}'

Notes

• Asset paths use UE content format: /Game/Folder/Asset
• File system paths use forward slashes: D:/Projects/file.png
• JSON params default to {} if omitted
• Commands run on the game thread — editor must not be in a modal dialog
• Use save_asset or save_all_dirty to persist changes
• call_function does not support latent functions (those with async/delay)