Content from 

https://confluence-test.ecmwf.int/display/ECC/Frequently+Asked+Questions

Summary

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  Creating your own local definitions - ecCodes GRIB FAQ — Local definitions are required when one needs to store information which is not part of the standard GRIB header. This might be local parameters or local definitions.
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  Failure setting key changeDecimalPrecision - ecCodes GRIB FAQ — If you issue the command "grib_set -s changeDecimalPrecision=1 spectral.grib output", you can get an error
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  Getting an "relocation R_X86_64_32 against `.bss' cannot be used when making a shared object; recompile with -fPIC" - ecCodes FAQ — jasper library that has been linked statically is trying to be linked into a dynamic libgrib_api.so. Libraries linked to a dynamic library must use "relocatable" code, and normally static libraries aren't. Possible solutions
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  grib_compare: index based comparison - ecCodes GRIB FAQ — Suppose you have two large GRIB files and their messages are not in order, how do you compare them? One technique is to build index files from inputs and then compare those index files.
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  grib_filter/bufr_filter: How can I check if a key exists (is defined) in a message - ecCodes GRIB FAQ — Easy peasy. Use the "defined" function which takes a single key name as argument. e.g.
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  grib_filter/bufr_filter: How do I control the format of array printing - ecCodes GRIB FAQ — One can add several 'modifiers' to a key in square brackets to control number of columns, separator string and format
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  grib_to_netcdf: "Wrong number of fields... Try using the -T option" - Web API FAQ
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  grib_to_netcdf: skips Control Forecast when I convert Ensemble Forecast data - ecCodes GRIB FAQ — If you have a file with both Control and Perturbed forecasts, grib_to_netcdf will only convert the pf. Normally from 51 members in the GRIB file, only 50 appear in the netCDF.
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  grib_to_netcdf: why are some fields filled with missing values - ecCodes GRIB FAQ
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  grib_to_netcdf: Why do I get the error "Wrong number of fields... Try using the -T option" - ecCodes GRIB FAQ — You try to retrieve data from the ECMWF data archive in netCDF format but the retrieval fails with this message
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  How can I catch assertion failures - ecCodes FAQ
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  How can I change from second order to simple packing - ecCodes GRIB FAQ — But this will not work and issue errors re codedValues and bitsPerValue! You need to use the repacking option as shown
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  How can I convert a multi-field GRIB file to single-field - ecCodes GRIB FAQ
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  How can I dump a given section - ecCodes GRIB FAQ
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  How can I find out which keys can be set to "missing" - ecCodes GRIB FAQ