The simplest way to invoke an external process in Groovy is to use the execute() command on a string. For example, to execute maven from a groovy script run this:
"cmd /c mvn".execute()
If you want to capture the output of the command and maybe print it out, you can do this:
print "cmd /c mvn".execute().text
The ‘cmd /c’ at the start invokes the Windows command shell. Since mvn.bat is a batch script you need this. For Unix you can invoke the system shell.