Re: [ferret_users] How can I check existence of a variable

[Ansley Manke <ansley.b.manke@xxxxxxxx>]

Hi Patrick,
That's a good idea, to have a RETURN hand us back the word ERROR; it 
would come in handy when writing scripts.

For your case, you can get the information you want right now, using the 
attribute-handling capabilities of Ferret. For a full description of all 
this, see section 3.1.8 in the Users guide - 
http://ferret.pmel.noaa.gov/Ferret/documentation/users-guide/variables-xpressions/VARIABLES#_VPINDEXENTRY_277

Scroll on down in this section to section 3.1.8.2, Attribute Keywords

We will be using the attribute keyword, varnames, to define a variable 
containing the names of the variables in the current dataset

  yes? use levitus_climatology.cdf
  yes? let allnames = ..varnames  

  yes? let temp_exists = IS_ELEMENT_OF_STR (allnames, "TEMP")

Note that this is case-sensitive -- we could use a version of the 
IS_ELEMENT_OF_STR function which makes a case-insensitive comparison, 
but you could of course do

  yes? let temp_exists = `IS_ELEMENT_OF_STR (allnames, "TEMP") OR \
       IS_ELEMENT_OF_STR (allnames, "TEMP")`


Ansley


Brockmann Patrick wrote:
> Hi all,
>
> In 2005, someone asks how to check if a variable exists.
> Read 
> http://www.pmel.noaa.gov/maillists/tmap/ferret_users/fu_2005/msg00828.html 
>
>
> I have tried to use return value but the error message is not trappable
>
> yes? use levitus_climatology.cdf
> yes? def sym isexist=`temp,return=dsetnum`
> !-> def sym isexist=1
> yes? def sym isexist=`abcd,return=dsetnum`
> **ERROR: variable unknown or not in data set: ABCD
>
> So is there a way to improve return value mechanism to trap the error 
> message
> and get a return value set to "ERROR". It would be easy then to test 
> it with
> a simple test:
>
> check.jnl
>
> def sym isexist=`($01),return=dsetnum`
> if `"($isexist)" eq "ERROR"` then
>        say "($01) does not exist"
> elif
>        say "($01) exists"
> fi
>
> Thanks
> Patrick