How to count lines all text file in a directory and subfolders

Question

I'm trying to improve a script posted by @Tony in other question

  @Echo off
  Set _File=file.txt
  Set /a _Lines=0
  For /f %%j in ('Type %_File%^|Find "" /v /c') Do Set /a _Lines=%%j
  Echo %_File% has %_Lines% lines.

To count lines all text file in a directory and subfolders:

  @Echo off
  setlocal EnableDelayedExpansion
  Set _Dir=C:\TEST_DIR\
  Set /a _Lines=0
  for /R %_Dir% %%f in (*.*) do (
    for /f %%j in ('Type !%%f!^|Find "" /v /c') Do Set /a _Lines=!_Lines!+!%%j!
  )
  Echo %_Dir% has %_Lines% lines.
  pause

But I'm geting error: "Missing operand."

Answer 1

My bad, I'm was using extra !! in the sentence:

Do Set /a _Lines=!_Lines!+!%%j!

This is the working code:

@Echo off
Set _Dir=C:\TEST_DIR\
Set /a _Lines=0
for /R %_Dir% %%f in (*.*) do (
  for /f %%j in ('Find "" /v /c ^< "%%~f"') Do Set /a _Lines=_Lines+%%j
)
Echo %_File% has %_Lines% lines.
pause

[EDITED] as @aschipfl sugested