Batch file check if file overwrote properly

Question

I need to save a file by copying it to a .bak in a batch file.

I then need to check if my file overwrote properly the existing .bak. Simply comparing the files could not be working, as it is possible for the user to save it twice in a row with no changes.

What I already have is:

type carnet.txt > carnet.bak

or this which works too:

copy carnet.txt carnet.bak

But it does not check if the file was really overwrote.

Answer 1

 copy carnet.txt carnet.bak
 FC /b carnet.txt  carnet.bak | FIND "FC: no dif" > nul 
 IF ERRORLEVEL 1 ( echo "files are different" ) else ( echo "successful backup" )

more for FC command