Batch Files - Error Handling

Question

I'm currently writing my first batch file for deploying an asp.net solution. I've been Googling a bit for a general error handling approach and can't find anything really useful.

Basically if any thing goes wrong I want to stop and print out what went wrong.

Can anyone give me any pointers?

Answer 1

A successful ping on your local network can be trapped using ERRORLEVEL.

@ECHO OFF
PING 10.0.0.123
IF ERRORLEVEL 1 GOTO NOT-THERE
ECHO IP ADDRESS EXISTS
PAUSE
EXIT
:NOT-THERE
ECHO IP ADDRESS NOT NOT EXIST
PAUSE
EXIT

Answer 2

Its extremely easy! Create a file that contains:

call <filename>  // the file you made
cls
echo An error occured!
<Your commands>
pause

So now when you start it, it will launch your program as normal. But when anything goes wrong it exits and continues the script inside the first file. Now there you can put your own commands in.

Answer 3

I guess this feature was added since the OP but for future reference errors that would output in the command window can be redirected to a file independent of the standard output

command 1> file - Write the standard output of command to file

command 2> file - Write the standard error of command to file

Answer 4

Python Unittest, Bat process Error Codes:

if __name__ == "__main__":
   test_suite = unittest.TestSuite()
   test_suite.addTest(RunTestCases("test_aggregationCount_001"))
   runner = unittest.TextTestRunner()
   result = runner.run(test_suite)
   # result = unittest.TextTestRunner().run(test_suite)
   if result.wasSuccessful():
       print("############### Test Successful! ###############")
       sys.exit(1)
   else:
       print("############### Test Failed! ###############")
       sys.exit()

Bat codes:

@echo off
for /l %%a in (1,1,2) do (
testcase_test.py && (
  echo Error found. Waiting here...
  pause
) || (
  echo This time of test is ok.
)
)

Answer 5

Other than ERRORLEVEL, batch files have no error handling. You'd want to look at a more powerful scripting language. I've been moving code to PowerShell.

The ability to easily use .Net assemblies and methods was one of the major reasons I started with PowerShell. The improved error handling was another. The fact that Microsoft is now requiring all of its server programs (Exchange, SQL Server etc) to be PowerShell drivable was pure icing on the cake.

Right now, it looks like any time invested in learning and using PowerShell will be time well spent.

Answer 6

I generally find the conditional command concatenation operators much more convenient than ERRORLEVEL.

yourCommand && (
  echo yourCommand was successful
) || (
  echo yourCommand failed
)

There is one complication you should be aware of. The error branch will fire if the last command in the success branch raises an error.

yourCommand && (
  someCommandThatMayFail
) || (
  echo This will fire if yourCommand or someCommandThatMayFail raises an error
)

The fix is to insert a harmless command that is guaranteed to succeed at the end of the success branch. I like to use (call ), which does nothing except set the ERRORLEVEL to 0. There is a corollary (call) that does nothing except set the ERRORLEVEL to 1.

yourCommand && (
  someCommandThatMayFail
  (call )
) || (
  echo This can only fire if yourCommand raises an error
)

See Foolproof way to check for nonzero (error) return code in windows batch file for examples of the intricacies needed when using ERRORLEVEL to detect errors.