First of all, if you are not using the Force.com Migration Tool (ANT) to deploy metadata changes... you should. You use the Metadata API to retrieve, deploy, create, update or delete customization information, such as custom object definitions and page layouts, for your salesforce.com org. This API is intended for managing customizations and for building tools that can manage the metadata model, not the data itself.
The easiest way to access the Metadata API is to use the Force.com IDE or Force.com Migration Tool. The Force.com Migration Tool is ideal if you want to use a script or a command-line utility for moving metadata between a local directory and a salesforce organization. A number of new developers on the Force.com platform seem to shy away from using the ANT tool so I wanted to provide a quick tutorial showing how easy it is to use the ANT version. You can find out how to download, configure and run at from the Force.com Migration Tool page.
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