powershell script to export the sitecollection & its conten

 Hi all,

            I have a requirement like, have to get the sharepoint sitecollection and all its contents like lists and its items etc... into xml or any other formats, like the SQL server create script does , and I have to restore the same script with some changes or adding new stuffs to the some other site collection in another environment.Any guidance or suggestions would be helpful.Thanks in advance.