How do I use environment variables in an Eclipse .classpath file?

In Windows I have an environment variable EXTERNAL_LIB_ROOT that points to C:\Program Files\MyExternalLibRoot. On another machine, it may point to C:\ExternalLibs.

In an ant build.xml file I would use:

<pathelement location="${env.EXTERNAL_LIB_ROOT}/path/to/jar.jar"/>

How do I set up an Eclipse project .classpath file to use the EXTERNAL_LIB_ROOT environment variable? Is it possible to have Eclipse auto generate the build.xml file using the environment v开发者_运维知识库ariable as above?

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Not an environment variable, but you can set up a Path Variable in Eclipse. Path variables are per-workspace. They are therefore a convenient way of sharing a common location among multiple projects within a workspace. I have used them to share a lib folder among projects.

To create a Path Variable (either for the first time, or to re-use an existing one in a project):

• File / New / Folder
  • Opens the New Folder dialog
• Click on the Advanced button
• Select the "Link to folder in the file system" check box
• Click the Variables button
  • Opens the Select Path Variable dialog
• Select or create a Path Variable

In your case, create a variable called EXTERNAL_LIB_ROOT.

(BTW, rather than generating a build.xml from your .classpath, I would suggest instead creating .classpath and .project from your build.xml.)

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Maybe the Ant addon Ant4Eclipse will help you, see
http://www.ant4eclipse.org/userguide-jdt and jdtClassPathVariable