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Batch Script Debugging

Batch Script Debugging​

Debugging is important because it allows to discover and to fix errors in a program before releasing it to the public.

As in any programming language, debugging is also possible in batch scripts.

You can debug in different ways:

  • Using echo command
  • Using pause command
  • Logging the error messages to another file
  • Using ErrorLevel to detect errors and log them

Using echo command​

The easiest way to debug is to use the echo command in batch scripts.

It will display the message in the command prompt and help you debug where things have gone wrong.

In the following example

example-echo.bat
@echo off  
if [%1] == [] ( 
   echo input value not provided 
   goto stop 
)  
rem Display numbers 
for /l %%n in (2,2,%1) do ( 
   echo %%n 
)  
:stop 
pause 
C:\>example-echo.bat
10
2
4
6
8
10
22
Press any key to continue ...

Using pause command​

Another way is to pause batch execution when an error occurs. When the script is paused, the developer can fix the problem and restart processing.

In the following example, the batch script is paused because the input value is mandatory and is not provided.

example-pause.bat
@echo off  
if [%1] == [] ( 
   echo input value not provided 
   goto stop 
) else ( 
   echo "Valid value"     
)  
:stop 
pause 
C:\>example-pause.bat
input value not provided
Press any key to continue..

Logging the error messages to another file​

It may be difficult to debug the error just by looking at a bunch of echoes displayed in the command prompt. Another simple solution is to record the messages in another file and view them step by step to understand what went wrong.

For example, the command given in the .bat file is wrong:

example-log.bat
net statistics /Server

so we can log it and then see what we get:

C:\>example-log.bat > testlog.txt 2> testerrors.txt

The file testerrors.txt will display the error messages as shown below:

The option /SERVER is unknown.
The syntax of this command is:
NET STATISTICS
[WORKSTATION | SERVER]
More help is available by typing NET HELPMSG 3506.
note

Looking at the testlog.txt and testerrors.txt files the developer can fix the program and execute again.

Using ErrorLevel to detect errors and log them​

Errorlevel returns 0 if the command executes successfully and 1 if it fails.

Consider the following example:

example-errorelevel.bat
@echo off
PING google.com
if errorlevel 1 GOTO stop
:stop
echo Unable to connect to google.com
pause

During execution, you can see errors as well as logs:

C:\>example-errorelevel.bat > testlog.txt

And the output is inside the textlog.txt file:

Pinging google.com [172.217.26.238] with 32 bytes of data:
Reply from 172.217.26.238: bytes=32 time=160ms TTL=111
Reply from 172.217.26.238: bytes=32 time=82ms TTL=111
Reply from 172.217.26.238: bytes=32 time=121ms TTL=111
Reply from 172.217.26.238: bytes=32 time=108ms TTL=111
Ping statistics for 172.217.26.238:
Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
Minimum = 82ms, Maximum = 160ms, Average = 117ms
Connected successfully
Press any key to continue . . .

In case of failure, you will see the following logs inside testlog.txt.

Ping request could not find host google.com. Please check the name and try again.
Unable to connect to google.com
Press any key to continue . . .

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