How do I make a log of all ECHO commands in a BATCH file?

for this purpose I use the following:

set LogFile=somepath\logfile.txt
set logg=^> _^&type _^&type _^>^>%LogFile%
echo this goes to screen AND file! %logg%

This is a bit tricky. So let's disassemble that line to four parts:

set logg=      ^> _          ^&type _           ^&type _^>^>%LogFile%

The Idea is to print the line to a temporary file (named _) (second part) then type the contents of that file to screen (third part) then type it to the logfile (fourth part).

Put that all to a variable (first part), so you don't have to type that monsterstring to every line. (this is the reason why the > and & are escaped with ^)

So every time you use

echo whatever %logg%

it will appear on the screen AND write to %logfile%

Note that this will also work:

 %logg% echo whatever

Edit djangofan: Also, you can do it with functions:

@ECHO off
:: do not enable delayed expansion since it will break this method
SETLOCAL ENABLEEXTENSIONS
SET LogFile=logfile.out
SET Logg=^> tmp.out^&^& type tmp.out^&^&type tmp.out^>^>%LogFile%

CALL :logit "This is my message!"
CALL :logit "Hear my thunder?"

GOTO :end
:logit
ECHO %~1 %Logg%
DEL /Q tmp.out
EXIT /B 0
:end
pause

Edit Stephan: If you use CALL, the %logg% would be overkill. In that case I would just use:

:logit
echo %~1
echo %date%,%time% - %~1 >>logfile
exit /b 0

This might be the best solution to the original question, because the Date/Time will be written into logfile, but not on the screen. Btw: you don't have to delete the tempfile every time you use it, just delete it one time, just before the batch ends.

As my other answer got quite long due to some edits, here is a new suggestion (not much changed, but it makes the code quite easy to read):

@ECHO off
SET LogFile=logfile.out
set "say=call :logit "

%say% "This is my message!"
%say% "Hear my thunder?"

GOTO :end
:logit
ECHO %~1 
echo %date% %time% - %~1 >>%logfile%
EXIT /B 0
:end