[ferret_users] Masking a file variable and append

[Dumont Dany <Dany.Dumont@xxxxxxxxxxx>]

Dear ferreters,

I want to apply a mask to a variable where it is equal to zero and then append the change to the same file. I use the following script, but the resulting file remains unchanged. What do I do wrong and what should I do?

'
use grid_spec.nc
set list/format=cdf
set memory/size=100
set variable/bad=0 depth_t
define att/type=float depth_t.missing_value = -1.e34
list/file=grid_spec.nc/append
exit
'

The change is done after the line 'define attribute/...', i.e. the attribute is correctly shown when I type 'show data/attr' and the variable is effectively masked. However, the change is not saved to the file. The original file has a lot of variables (about a hundred) and I don't want to list them all.
Thanks,

Dany