The NCL development people [via Rick Grubin] have asked for user
input before deciding which direction they should proceed with
Command Line Options (CLOs). Based upon experience teaching NCL,
I offer the following comments to ncl-talk (like Christian
Marquardt) rather than replying directly to Rick.
(1) Most students are science oriented people. The vast majority
do not know languages like Perl or Python. Some are familiar
with shell programming [eg: C-shell] but are from from experts.
Generally the students include: grad student, post-docs,
research scientists and operationally oriented people.
(2) The people who have requested CLOs in the classes have requested
simple features.
(3) They would like something "sooner-than-later".
Implementing a simple interface that does not preclude
adding more sophisticated capabilities at a later time
would be my choice.
(4) One simple approach that is consistent with how NCL currently
does things is:
opt = GetOpt( optName:string, optType:string)
For the sake of discussion:
Predefined opts are capitals, eg: If P did not appear on the options
list, then, if the user queries the CL via GetOpt and no "P" was there, it
would default to (say) "ps"; "S" - would be the script
name ; "V" - NCL version which would be a string.
examples, the defaults for predefined option are in [...]
fil = GetOpt("F" , "string") ; -F foo.nc ["missing"]
pType = GetOpt("P" , "string") ; -P X11 ["ps"]
sName = GetOpt("S" , "string") ; -S ["missing"]
vName = GetOpt("V" , "string") ; -V
n = GetOpt("navg" , "integer") ; -navg 5
con = GetOpt("constant", "float") ; -con 3.75
cyc = GetOpt("cyclic" , "logical") ; -cyclic True
non-predefined options can be set to the NCL default type
fruitType = GetOpts("fruit", "string")
and if "fruit" was not on the CL then fruitType would be
set to "missing" which is the default _FillValue for a
variable of type string.
(5) A nice feature might be to allow wild cards on the CL
-F foo1.nc,foo2.nc,foo3.nc [explicit file naming]
-F foo*.nc [wild card]
-F foo[1-3].nc [another wild card]
fils = GetOpt("F" , "string")
(6) Most users are not aware of the single and/or double dash
options and will cheerfully [ :-) ] adapt to whatever is presented.
(7) More sophisticated approaches, such as, getting all the options
at once would be nice but, IMHO, not at the expense of delayed
implementation of CLOs.
options = ("option-1", "option-2", ... "option-N")
Since NCL does not allow arrays of mixed type [ie, structures],
"options" would be an array of strings.
Comments to ncl-talk are welcome.
Dennis Shea
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