This function creates a new file or opens an existing file.
            Examples
            In this example, we create a new swath file named, SwathFile.hdf. It returns the file handle, fid:
            fid = EOS_SW_OPEN("SwathFile.hdf", /CREATE)
            Syntax
            Result = EOS_SW_OPEN( filename [, /CREATE] [, /RDWR | , /READ] )
            Return Value
            Returns the swath file id handle (fid) if successful and FAIL (–1) otherwise.
            Arguments
            filename
            Complete path and filename for the file to be opened (string).
            Keywords
            CREATE
            If file exists, delete it, then open a new file for read/write.
            RDWR
            Open for read/write, If file does not exist, create it.
            READ
            Open for read only. If file does not exist, error. This is the default.
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