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// $Id: Env.java,v 1.4 2003/10/07 21:46:09 idgay Exp $

package net.tinyos.util;

/**
 * The Env class provides an implementation of
 * getenv that actually works, unlike the one in
 * java.lang.System.  The class cannot be instantiated.
 *
 * V1.1: provide wrapper so that getenv doesn't fail horribly when the
 * native code is not found.
 *
 * @author   R M Yorston, David Gay
 * @version  1.1
 */
public class Env {
    static private boolean loaded;
    static {
	try {
	    java.lang.System.loadLibrary("getenv");
	    loaded = true;
	}
	catch (Throwable t) {
	    System.err.println("getenv JNI library not found. Env.getenv will not work");
	    System.err.println("(please consult installation directions in");
	    System.err.println("tinyos-1.x/tools/java/net/tinyos/util/Env.INSTALL)");
	}
    }

    private Env() {
    }

    /**
     * Gets an environment variable. An environment variable is a
     * system-dependent external variable that has a string value.
     *
     * @param	name	name of the environment variable
     * @return	the value of the variable, or null if the
     * variable is not defined.
     */
    public static String getenv(String name) {
	if (loaded) {
	    return igetenv(name);
	}
	else {
	    return null;
	}
    }

    private static native String igetenv(String name);
}