getenv.java

JAVA 数学程序库 提供常规的数值计算程序包

package jmathlib.toolbox.jmathlib.system;

import jmathlib.core.interpreter.*;
import jmathlib.core.functions.ExternalFunction;
import jmathlib.core.tokens.Token;
import jmathlib.core.tokens.CharToken;
import jmathlib.core.tokens.OperandToken;

/**External function to get a enviroment variable*/
public class getenv extends ExternalFunction
{
	/**Returns an enviroment variable
	@param operand[0] = the name of the variable
	@param operand[1] = a default value (optional)
	@return the enviroment value*/
	public OperandToken evaluate(Token[] operands)
	{
		OperandToken result = null;
		
		if(operands[0] instanceof CharToken)
		{
			String name = operands[0].toString();
			String defaultVal = "";
			
			if(operands.length > 1)
			{
				defaultVal = operands[1].toString();
			}
			
			String property = System.getProperty(name, defaultVal);
			
			result = new CharToken(property);
		}
		else
			Errors.throwMathLibException(ERR_INVALID_PARAMETER, new Object[] {"CharToken", operands[0].getClass().getName()});
			
		return result;
	}
}

/*
@GROUP
system
@SYNTAX
GETENV(variablename)
@DOC
Returns the value of the enviromental variable variablename.
@NOTES
@EXAMPLES
GETENV("HOME")= "/home/user"
@SEE
*/