How to convert fixed size dimension to unlimited in a netcdf file
linux, nco, netcdf, sed
Solution
Your answers are very insightful. I'm not really looking a way to improve this ncdump-sed-ncgen method, I know that dumping a netcdf file that is 600MB uses almost 5 times more space in a text file (CDL representation). To then modify some header text and generate the netcdf file again, doesn't feels very efficient.
I read the latest NCO commands documentation, and found a option specific to ncks "--mk_rec_dmn". Ncks mainly extracts and writes or appends data to a new netcdf file, then this seems the better approach, extract all the data of myfile.nc and write it with a new record dimension (unlimited dimension) which the "--mk_rec_dmn" does, then replace the old file.
ncks --mk_rec_dmn time_counter myfile.nc -o myfileunlimited.nc ; mv myfileunlimited.nc myfile.nc
To do the opposite operation (record dimension to fixed-size) would be.
ncks --fix_rec_dmn time_counter myfile.nc -o myfilefixedsize.nc ; mv myfilefixedsize.nc myfile.nc
Problem
I'm downloading daily 600MB netcdf-4 files that have this structure: ``` netcdf myfile { dimensions: time_counter = 18 ; depth = 50 ; latitude = 361 ; longitude = 601 ; variables: salinity temp, etc ``` I'm looking for a better way to convert the time_counter dimension from a fixed size (18) to an unlimited dimension. I found a way of doing it with the netcdf commands and sed. Like this: ``` ncdump myfile.nc | sed -e "s#^.time_counter = 18 ;#time_counter = UNLIMITED ; // (currently 18)#" | ncgen -o myfileunlimited.nc ``` which worked for me for small files, but when dumping a 600 MB netcdf files, takes to much memory and time. Somebody knows another method for accomplishing this?