Because WinSCP manages to delete the local temporary copy before BC reads it.

You have to workaround it somehow:

• wait a bit before exiting the command, like

  cmd /c start "" "C:\Program Files (x86)\Beyond Compare 3\BCompare.exe" "!" "!^!" & timeout /t 3

  
  
• copy the file elsewhere and compare the copy
  

now the command executes without displaying the custom command message, but the remote screen is always blank, like it does not know where to find the source. If I run the command without 'start', the compare works normally. I have several tabs open, so perhaps it does not know which remote session to use for the compare? Two images are attached from running with and without 'start'. The temporary file names are pointing to different folders

The correct syntax is:

When I added "cmd.exe /c start " to the front of my command, winSCP invoked Textpad against the files I was trying to compare. Here is my command string

cmd /c start "C:\Program Files (x86)\Beyond Compare 3\BCompare.exe" "!" "!^!" &

Use the start command to prevent that.

See https://winscp.net/eng/docs/guide_custom_commands_automation#general_hints

I use winscp to call BeyondCompare, but whenever I am comparing a Local file to a remote file, I see the 'executing custom command' message, which locks me out of doing anything else. Can I avoid this so that I can still manipulate files via WinSCP while the remote command is executing, like a background process, maybe?