[ferret_users] How to check whether the attribute is defined in dataset or not, and how to save all global attributes in variable/array

To: ferret_users <ferret_users@xxxxxxxx>

Subject: [ferret_users] How to check whether the attribute is defined in dataset or not, and how to save all global attributes in variable/array

From: Akshay Hegde <akshay.k.hegde@xxxxxxxxx>

Date: Thu, 11 May 2017 18:21:09 +0530

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1. Is it possible to save the output of show attr/all . to some variable like let foo = ..varnames
2. How to check whether the attribute is defined in dataset (Global attributes) or not.

For Example :

As you can see below attribute history exists in dataset, so it doesn't throw any exception, but say if I type list ..someother_attr, I get error since it doesn't exist, so is there any way to check whether attribute exists in dataset.

yes? use coads_climatology;
yes? show d
     currently SET data sets:
    1> /usr/local/ferret/fer_dsets/data/coads_climatology.cdf (default)
name     title                             I         J         K         L         M         N
SST      SEA SURFACE TEMPERATURE          1:180     1:90      ...       1:12      ...       ...
AIRT     AIR TEMPERATURE                  1:180     1:90      ...       1:12      ...       ...
SPEH     SPECIFIC HUMIDITY                1:180     1:90      ...       1:12      ...       ...
WSPD     WIND SPEED                       1:180     1:90      ...       1:12      ...       ...
UWND     ZONAL WIND                       1:180     1:90      ...       1:12      ...       ...
VWND     MERIDIONAL WIND                  1:180     1:90      ...       1:12      ...       ...
SLP      SEA LEVEL PRESSURE               1:180     1:90      ...       1:12      ...       ...

yes? show att/all .
     attributes for dataset: /usr/local/ferret/fer_dsets/data/coads_climatology.cdf
..history = FERRET V4.45 (GUI) 22-May-97
yes? list ..history
             VARIABLE : ..HISTORY
             FILENAME : coads_climatology.cdf
             FILEPATH : /usr/local/ferret/fer_dsets/data/
             X        : 1
        "FERRET V4.45 (GUI) 22-May-97"
yes? list ..someother_attr
**ERROR: attribute undefined or invalid attribute name: ..SOMEOTHER_ATTR
          attribute SOMEOTHER_ATTR not found for dataset
**ERROR: variable unknown or not in data set: ..SOMEOTHER_ATTR

I can check from outside using spawn like below

[akshay@localhost tmp]$ ncdump -h /usr/local/ferret/fer_dsets/data/coads_climatology.cdf | grep -q ':something' && echo 'exists' || echo 'does not exist';
does not exist

[akshay@localhost tmp]$ ncdump -h /usr/local/ferret/fer_dsets/data/coads_climatology.cdf | grep -q ':history' && echo 'exists' || echo 'does not exist';
exists

Thank you.

Regards,

Akshay Hegde,

Data and Information,

CSIR-NIO
https://about.me/akshay.k.hegde