Batch file compare returning 0 when files are different

Question

I use a scheduling system on a Windows 2003 server that requires batch files to run different jobs. I have one job that checks if a file exists, compares that the file is not empty, then does something based on the results. Each time I run this, the error level returned is 0, but the files are different. I'm expecting to see a 1 returned.

I've verified the location of the files, and one file has content and the other is empty. I've setup prompts, and they they all say %ERRORLEVEL% is 0. I even moved the files to be in the same directory at the batch job, but they still show 0.

The code:

echo %ERRORLEVEL%
IF EXIST data.DON ( 
echo before %ERRORLEVEL%
    FC data.DON ZERO.SEQ
echo after %ERRORLEVEL%
    IF %ERRORLEVEL% EQU 1 GOTO :PROCESS
)

The output:

16:37:08.12 Thu 03/29/2012
>IF EXIST data.DON (
echo before 0  
 FC data.DON ZERO.SEQ  
 echo after 0  
 IF 0 EQU 1 GOTO :PROCESS 
) 
before 0
Comparing files data.DON and ZERO.SEQ
***** data.DON
Name|Date|Location    

***** ZERO.SEQ
*****

after 0

I have this exact code in other jobs on the same server pointing at different data files, and it works. Any ideas of what I can try?

Answer 1

If you replace the value of any %variable% inside parentheses, that value is the same the variable had before enter the parentheses:

set var=Old value
( set var=New value & echo %var% )

Previous code always show: Old value

To solve this problem you must use Delayed Expansion, that is, enclose the variable in exclamation marks instead percents and add a SETLOCAL command at beginning:

setlocal EnableDelayedExpansion
set var=Old value
( set var=New value & echo !var! )

All previous description also apply to errorlevel variable, so replace all %errorlevel% by !errorlevel! in your code and insert the previous SETLOCAL ....

Answer 2

The correct way to check errorlevel is like this:

IF EXIST data.DON ( 
    FC data.DON ZERO.SEQ
    IF ERRORLEVEL 1 GOTO :PROCESS
)