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COPYBOOKs are code that is kept in a common library (COPYlib) and is expanded in COBOL code using the COPY command.
COPY is used when the same code (i.e. a record layout) is to be used in multiple programs. Using a copybook allows the code to be maintained in one place, but used in all of the programs that need that same code. This can be any kind of code that is used multiple places, not only records layouts.
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