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Output is written to output_index_file. If an output index file is required and -o is not used, the output index is written to 'gribidx'
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Specify a list of keys to index on. By default the input files are indexed on the MARS keys. For each key a string (key:s) or a double (key:d) or an integer (key:i) type can be requested.
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Multi-field support off. Turn off support for multiple fields in single grib GRIB message.
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Do not compress index. By default the index is compressed to remove keys with only one value.
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