Question

I’ve not had to write much batch file code in the past and I’m trying to understand why someone else’s code has failed by writing a test batch file. My code:

:DoUntil
type p.txt >> log.txt
if %ERRORLEVEL% EQU 0 goto DoUntil

ECHO %ERRORLEVEL%

p.txt is an existing text file with a simple character string as is log.txt.

I then run this twice to get the error:

The process cannot access the file because it is being used by another process.

As you’d expect. Now I expected ERRORLEVEL to be set and a value returned by the echo, so what am I doing wrong please in ordered to get this echo’d as I expected? (it never hits the echo)

Or is there anywhere I can get a list of "type"s possible return value? I’ve found Googling on this subject quite frustrating due to how commonly used all the terms are! I read a few other questions on here which helped me correct one problem with my sample code but not the fundamental.

Edit:

Jeb’s answer below was perfect in answering my query but I’m failing to take it forward. The problem code we have is like:

:DoUntil
type p.txt >> log.txt
if ERRORLEVEL 1 goto DoUntil

So the code is trying to say "if type fails, retry until it works". Are we saying by not having the "|| rem" clause+empty statement at the end of the type that the if statement is essentially doing nothing?

Answer 1

There seems to be a bug/feature exists with errors from redirections. So you need a small trick to get the errorcode.

:DoUntil
type p.txt >> log.txt || rem
if %ERRORLEVEL% EQU 0 goto DoUntil

ECHO %ERRORLEVEL%

It’s described by dbenham here