NCO: change the attribute value of variable with a new string containing blank space

Question

I have a netCDF file FORCING.nc which contains a variable time with attribute value units: hours since 2007-12-28 22:00:00. In python code, it is as following:

from netCDF4 import Dataset
Dataset('FORCING.nc')["time"]

and the output is:

Out[3]: 
<class 'netCDF4._netCDF4.Variable'>
float32 time(time)
    units: hours since 2007-12-28 22:00:00
unlimited dimensions: 
current shape = (13,)
filling on, default _FillValue of 9.969209968386869e+36 used

And I want to change the attribute of units from hours since 2007-12-28 22:00:00 to hours since 1996-01-01 22:00:00. And 1996-01-01 22:00:00 comes from a variable $start_date in bash script.

So I want to use something like:

ncatted -a units,time,o,c,'hours since '$start_date FORCING.nc

which gives the argument 'hours since '+$start_date to then catted command, indeed it is 'hours since 1996-01-01 22:00:00' . But I got the error message like:

ncatted: ERROR file start_date not found. It does not exist on the local filesystem, nor does it match remote filename patterns (e.g., http://foo or foo.bar.edu:file).
ncatted: HINT file-not-found errors usually arise from filename typos, incorrect paths, missing files, or capricious gods. Please verify spelling and location of requested file. If the file resides on a High Performance Storage System (HPSS) accessible via the 'hsi' command, then add the --hpss option and re-try command.

I guess it is because there is space between "hours since 2007-12-28" and "22:00:00". If I use ncatted -a units,time,o,c,'hours since 2007-12-28 22:00:00' FORCING.nc, it works fine. But how can I use $start_date? because start_date varies each time I run the code...

Thanks!

Answer 1

You're close! Try

ncatted -a units,time,o,c,'hours since '"$start_date" FORCING.nc

Shell quoting rules. Can't live with 'em, can't live without 'em.