How to specify a system independent classpath

Question

I need to run a java command with a custom classpath.

On Windows I need to type:

java -cp foo;bar

On Linux I need to type:

java -cp foo:bar

We currently have a .bat file containing the first version and a .sh file containing the second version. This works fine most of the time, but fails for git-bash on Windows, which needs a shell script with a semicolon delimiter.

Is there any system independent way to write such a classpath?

I would think of something like

java -cp foo -cp bar

but this does not this way.

Currently the only way I see is having some shell logic determining the OS and generating the correct command line from that.

Is there an easier way to do this the java way?

Answer 1

• Option 1: If you don't mind creating a jar before running, you could specify the classpath in a manifest file. Those paths are space-separated. (See Adding Classes to the JAR File's Classpath)

• Option 2 Add code for detecting OS using for instance uname. Then do either SEP=\; or SEP=: and use path${SEP}path. (See for instance How to check if running in Cygwin, Mac or Linux?)

• Option 3: Grep the java help output to see what separator character java expects:

  SEP=$(java -h |& grep "A [:;] separated" | grep -o "[:;]")
  

• Option 4: If you have the JDK installed, you can print the File.pathSeparator:

  echo "interface C { static void main(String[] a) { System.out.print(java.io.File.pathSeparator); }}" > C.java
  javac C.java
  java C
  rm C.{java,class}
  

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Note: Only the path separators, i.e. ; vs :, are platform specific. Forward slashes (i.e. some/class/path) work fine on all systems for separating directories.