I don't work in the DOS (Windows command (
CMD.EXE)) world too much these days, but I needed to today. The basic problem was that I needed to build an environment variable dynamically. In this case I was trying to build a variable named
CLASSPATH from a collection of Java JAR files in a sibling directory named
LIB. This variable had to be built correctly for my Java application to work properly.
I couldn't get a lot of obvious approaches to work, but then remembered I had seen a trick back in the release of Jakarta Tomcat 3.3.x. Sure enough it was in there, and I'd like to share it here.
To accomplish the desired effect you need two scripts. The first script is the one you want to build. In this case my script is named
runit.bat. It has a "
for" loop, and in that
for loop I call the second script (
CPAPPEND.BAT), like this:
REM runit.bat (by Alvin J. Alexander) REM REM SET THE CLASSPATH DYNAMICALLY REM REM Call the CPAPPEND.BAT program to build the JARS env variable, REM then append that variable to the CLASSPATH. REM To be clear, CPAPPEND.BAT builds the JARS variable. REM (Note: Borrowed this approach from the REM Jakarta Tomcat people - thanks!) REM set JARS= set CLASSPATH= for %%i in (..\lib\*.jar) do call cpappend.bat %%i set CLASSPATH=%JARS%;..\dist\myApplication.jar java com.devdaily.myapp.MainController
Hopefully that batch file (I want to call it a script, but this isn't Unix land) makes sense. I'm building the variable
CLASSPATH dynamically from a list of "
*.jar" files that are located in a sibling directory named "lib". This
CLASSPATH variable is needed by my Java application.
I wanted this approach because I hate to do things like this statically. If I did it with a static approach, I'd have to modify this script every time I added a new JAR file, and I sure don't like that approach. DOS is a little weak in this area, but the approach of using a separate batch file (
CPAPPEND.BAT) works around this weakness.
Right around this time you should be wondering what that file looks like, so here are the contents:
rem CPAPPEND.BAT rem rem Copyright 1999-2004 The Apache Software Foundation rem rem Licensed under the Apache License, Version 2.0 (the "License"); rem you may not use this file except in compliance with rem the License. rem You may obtain a copy of the License at rem rem http://www.apache.org/licenses/LICENSE-2.0 rem rem Unless required by applicable law or agreed to in writing, rem software distributed under the License is distributed on an rem "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS rem OF ANY KIND, either express or implied. rem See the License for the specific language governing rem permissions and limitations under the License. rem @echo off set JARS=%JARS%;%1
I've left the original license in the file to credit the source of this solution. As you can see it really only has one useful line, the last one. It just adds the parameter I call it with to a variable named JARS, and this is the same variable I use in the first (calling) script to later build my
So, if you want to build a
PATH, or any other environment variable dynamically in DOS (Windows
CMD.EXE) this idea should do the trick for you.
This is a very useful trick. Thanks for sharing.
It worked 1st time for me!