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

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.

Answer 2

Using ERRORLEVEL when it's available is the easiest option. However, if you're calling an external program to perform some task, and it doesn't return proper codes, you can pipe the output to 'find' and check the errorlevel from that.

c:\mypath\myexe.exe | find "ERROR" >nul2>nul if not ERRORLEVEL 1 ( echo. Uh oh, something bad happened exit /b 1 ) 

Or to give more info about what happened

c:\mypath\myexe.exe 2&1> myexe.log find "Invalid File" "myexe.log" >nul2>nul && echo.Invalid File error in Myexe.exe && exit /b 1 find "Error 0x12345678" "myexe.log" >nul2>nul && echo.Myexe.exe was unable to contact server x && exit /b 1