The growing needs in computational power to answer to the increasing number of on-line services and the complexity of applications makes it mandatory to build corresponding hardware infrastructures and to share several distributed hardware and software resources thanks to grid computing. To help with optimizing resource utilization, system virtualization is a more and more adopted technique in data centers. However, this software layer adds to the administration complexity of servers and it requires specific management tools to deal with hypervisor functionalities like live migration. To address this problem, we propose VMScript, a domain specific language for administration of virtualized grid infrastructures. This language relies on set manipulation and is used to introspect physical and virtual grid architectures thanks to query expressions and notably to modify VM placement on machines.