Java – Set CLASSPATH Variable for a Folder in Ubuntu

environment-variablesjava

I know that export CLASSPATH=/usr/local/java/tools.jar:$CLASSPATH will add tools.jar to the CLASSPATH, but i want to set folder to the CLASSPATH

like this

export CLASSPATH=/usr/local/java/lib/:$CLASSPATH

but its not working.

Best Answer

First, in general, setting the env var CLASSPATH usually causes more problems than it solves -- since not all app's want/need the same classpath, & often break when undesired or even unneeded jars are included in the classpath. A java app should only include the minimum number of jars it requires, no more, no less.

When you have specific, individual apps that do require that the classpath be set, then usually the command-line option is preferred: java -cp path1:path2:.... Desktop icons can have their command altered to include these options, or shell scripts can be modified to include these options.

That being said (and since there are always exceptions to the rule), then depending on the version of java (this requres java 6 or later), you can specify that a whole directory of jars be added to the classpath by adding a "*" at the end of a directory; e.g, the following:

 /dir1/foo.jar:/dir2/dir3:/dir5/dir6/*:etc...

Means:

/dir1/foo.jar - (the single jar) will be added to the classpath;
/dir2/dir3 - all un-jar'd classes in this directory will be added to the classpath (must be in proper package structure; e.g, com.my.Foo.class must be in /dir2/dir3/com/my/Foo.class)
/dir5/dir6/* - all jars in this directory (i.e., /dir5/dir6/*.jar) will be added to the classpath. Note that this "*" isn't a wildcard (you can't use f*.jar or even *.jar); it's a special character indicating "add all jars"

In general, if you have to add a whole directory of jars to the application's classpath, the app was not bundled correctly. Rather, the app should have a manifest containing the list of jars it depends on. Or at the very least, only one jar should be added to your classpath, and that jar can have in its manifest the whole list of jars in some subdirectory.

Using `direnv`

Install direnv, which is a tool for this purpose which is a statically linked executable that hooks into your shell (csh,bash, and the like)

sudo apt-get install direnv && echo "eval "$(direnv hook bash)"" >> ~/.bashrc

Now to whichever folder you'd like the environment variables to be set, add an .direnvrc file that must have valid bash syntax. For example of your case, you can load both pyenv's version management as well as your own variables by setting your .direnvrc to:

use_python() {
  local python_root=$PYENV_ROOT/versions/$1
  load_prefix "$python_root"
  if [[ -x "$python_root/bin/python" ]]; then
    layout python "$python_root/bin/python"
  else
    echo "Error: $python_root/bin/python can't be executed."
    exit
  fi
}
export CUSTOM_VAR="xyz";

You can see other examples at their wiki

_{^{Thanks to @ChrisKuehl in the comments for the suggestion}}

Another alternate approach would be to override the PROMPT_COMMAND (as suggested in the comments by @steeldriver) to point to a function that loads your environment variable up, by adding something like this to your .bashrc

prmfn() {
  if [ "$PWD" == "yourdirectorypath" ]; then
    export CUSTOM_ENV_VAR=value
  else
    unset CUSTOM_ENV_VAR
  fi
}

export PROMPT_COMMAND=prmfn

Now when you enter yourdirectorypath, it'll automatically set CUSTOM_ENV_VAR, when you exit out of it, it'll unset(remove) the variable, hence that variable is only available when the current directory is yourdirectorypath

Best Answer

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