ReplaceValueInPropertiesFile

//The following code replaces a value of a property in a property file, while keeping comments if exist
def fileName = 'test.properties'
def propertyKey = 'key'

def myFile = new File(fileName)
def fileText = myFile.text
matcher =  fileText=~propertyKey+"=(.*)"
result = matcher.replaceFirst(propertyKey+'=new value')
myFile.withWriter { myFile << result }