Re: [netcdfgroup] easy/quick way to get attribute value from shell?

• To: netcdfgroup@xxxxxxxxxxxxxxxx,
• Subject: Re: [netcdfgroup] easy/quick way to get attribute value from shell?
• From: Tom Roche <Tom_Roche@xxxxxxxxx>,
• Date: Sun, 20 May 2012 12:49:22 -0400

Tom Roche May 18, 2012 2:25 PM
>>> Is there an easy and quick way to *get* the value of [any
>>> attribute, by name] (whether global or variable) from a (bash)
>>> shell commandline or script?
...
>>> unless I need to run R for other reasons, I'm writing bash like

>>>  if [[ "$(ncdump -h ${F} | fgrep -e ${OUTPUT_VAR_NAME}:units)" =~ 
>>> "${OUTPUT_VAR_UNITS}" ]] ; then
>>>    echo -e 'output!'
>>>  fi

Roy Mendelssohn Fri, 18 May 2012 18:23:39 -0700
>> [ncks]
>> '-m'
>> Print variable metadata to screen (similar to ncdump -h).
...
>> '-P'
>> Print data, metadata, and units to screen.

These, like `ncdump`, generate composite output, from which the
attribute value must be extracted. Hence `ncks` provides no advantage
over `ncdump`: is that not readily apparent?

Henry Butowsky recommends a somewhat cleaner approach for getting an
attribute value

me@it:/tmp$ ncap2 -v -O -s 'print(N2O@var_desc)' 
./emis_mole_onlyN2O_windowed.ncf
> N2O@var_desc, size = 80 NC_CHAR, value = Denitrification_N2     
me@it:/tmp$ FOO="$(ncap2 -v -O -s 'print(N2O@var_desc)' 
./emis_mole_onlyN2O_windowed.ncf)"
me@it:/tmp$ echo -e "FOO='${FOO##*= }'"
FOO='Denitrification_N2     '

but still some processing (and prior knowledge of the output format) is
required. Ideally there would be a modifier for NCO print statements
with the semantics 'just give me the value'; for that matter, the API
could be more readily understandable--is the intent of something
called `ncap2` readily apparent? Ideally we could combine the
clarities of R package=ncdf4 and the NCO print statement, e.g.

ncatt_get 'N2O@var_desc' /path/to/file
or, for global attributes
ncatt_get '@NVARS' /path/to/file

that could be used like

if [[ "$(ncatt_get 'N2O@units' /path/to/file)" == 'kg/ha' ]] ; then
  # convert kg to mol
  # convert ha to map-scaled gridcell area
fi

FWIW, Tom Roche <Tom_Roche@xxxxxxxxx>

• References:
  • Re: [netcdfgroup] easy/quick way to get attribute value from shell?
    • From: Roy Mendelssohn
  • Re: [netcdfgroup] easy/quick way to get attribute value from shell?
    • From: Roy Mendelssohn
  • [netcdfgroup] easy/quick way to get attribute value from shell?
    • From: Tom Roche
  • Re: [netcdfgroup] easy/quick way to get attribute value from shell?
    • From: Tom Roche