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 variable as above?
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.)
Maybe the Ant addon Ant4Eclipse will help you, see
http://www.ant4eclipse.org/userguide-jdt and jdtClassPathVariable
来源：https://stackoverflow.com/questions/7742015/how-do-i-use-environment-variables-in-an-eclipse-classpath-file