Windows Batch File Programming Make You Mad!

If you are a programmer from C/C++ or other advanced programming language, you might found that the Windows batch file programming is extremely madding.

Here is a list of the perplexing part of the Windows batch file programming that may make you mad.

Comments

You will find that the Windows batch files starts a comment line by "rem".
That is boring! A simple way to start a comment is "::".

:: This is a comment line

:: This is another comment.

Echo a empty line

To echo a empty line, you might think the follow would work.

echo

but it just report echo status. Actually you should use this.

echo.

The if...else...block

The right way to write a if...else...block is.

if exist "a.txt" (

    echo deleting...

    del a.txt

) else (

    echo already done!

)

Note, you must use "(" and ")" here.

How to check if a directory is exist

This code

if exist "path\to\dir" (

    echo Yes

) else (

    echo No

)

will print Yes **when a directory or file named "dir" were exist at path "path\to". So you can use this to check a folder's existence. To do so append a "\NUL**" at the of the path.

if exist "path\to\dir\NUL" (

    echo Yes

) else (

    echo No

)

The string substitute

To substitute a string, you should use

set VAR=%VAR:str1=str2%

This will replace all str1 in %VAR% with str2, and then assign the result to VAR.

The !VAR! doesn't work

The !VAR! (delayed environment variable expansion) usually don't work for you, because the "delayed environment variable expansion" feature is not enabled by default. You will find this is really boring. There is 2 way to enable the "delayed environment variable expansion", so far as I know.

  • using /V:ON switch to invoke the cmd.exe
  • add a DWORD registry key named DelayedExpansion under HKLM\Software\Microsoft\Command Processor (or HKCU), and set the key value to 1.

I prefer the former:

set TEST=any-string

if not "!TEST!"=="%TEST%" (

    %COMSPEC% /V:ON /C %~dpnx0 %*

    goto :eof

)

:: normal process code here...

The if statement is checking if the "delayed environment variable expansion" if work or not. If no, just call the %COMSPEC% (cmd.exe) with /V:ON and execute this batch itself with the same command line arguments.

The multipurpose for command

To be updated!