adding an environment variable using groovy

I'm trying to add an environment variable on my machine using a groovy script.

I can't add a shell script to call by my groovy....

I tries System.setParameter but the variable was not accessible by other processes in my machine.

this is my best shot so far, but it still not working.

 ant = new AntBuilder()
      ant.exec(executable:"sh"){
        arg(value:"export var1="+val1)
        arg(value:"export var2="+val2)
     }