Hiding information and hiding errors

While undoubtedly one of the fundamental uses of ddkbuild is as a wrapper of the BUILD utility from the DDK, there are things to do before and after calling. Some of these things involve ugly messages that be better hidden from the end user. As an example we can have a look at the code that tries to check whether the FINDSTR utility is available on the users' systems:

findstr /? > NUL 2>&1 || echo "Error" && goto :EOF

This line is pretty simple and and any Bash afiniciados might readily be able to decipher it without further comment. The part before the two pipe characters attempts to call FINDSTR and redirects its STDOUT as well as STDERR to NUL (which, btw, is the name of a pseudo-file in every single directory on a Windows system). 2>&1, similar to the Bash syntax actually says to redirect STDERR (handle 2) to the same pipe as STDOUT (handle 1).

The two consecutive pipe characters tell the script interpreter to only run the code to the right of it if the ERRORLEVEL variable (i.e. the exit code of the attempted execution of FINDSTR) is zero. This means that the command left of those pipe characters executed successfully. This trick also works for most other commands/executables and in fact ddkbuild uses it to check whether the REG.EXE utility is available. While existent in Windows XP, on some Windows 2000 systems it is only part of the supplementary tools from the install CD.

Use :: instead of REM

REM, meaning "remove", denotes a comment line in batch scripts and is also available in NT scripts for compatibility reasons. However, in NT scripts you have the option of using the more readable syntax with :: instead.

Technically lines starting with : are labels and :: is an invalid label. See this Stackoverflow question and its answers for more details.

Using :: to start a comment line makes the whole script more readable, however, because it is more distinct from other commands that are usually comprised of words or parts of words (call them mnemonics if you like). REM just looks like any other command and therefore you are often at a loss in long scripts if your editor doesn't have syntax highlighting for NT scripts.

Sadly though, many editors still don't support these makeshift comments in their syntax highlighters.

Using subroutines

Just like with real programming languages, GOTO is usually not the way to do things anymore, although it is often more convenient than not using it.

I suggest you get and read the book "NT Shell Scripting" for a primer on how to use subroutines in batch and NT scripts. The CALL command can not just be used to call external scripts (if you simply called and external script without CALL, the execution could potentially get stuck in the other script and never return). CALL can also be used to call subroutines - aka "labels" - similar to the way you can use GOTO.

If you define a particular label and end its execution path by a GOTO :EOF, the latter one can be used in the same way as "return" in other languages.

In this case :EOF is an implicitly defined label created by the interpreter.

There is only a minor caveat with this approach in that the flow of execution before any subroutines has to be ended by GOTO :EOF as well, because it would otherwise run into the first of the subroutines.

Furthermore subroutines take their own set of parameters that can be addressed using the variables %1 through %9 and used within the routine using the syntax described under FOR /?, such as %~1 in order to remove the outer double quotes from the parameter. This is a pretty neat feature for normalization of parameters or processing of file names.