Re: way to find out if variable has been defined

[Juhász P. <pet...@gm...>]

On Tue, 2012-01-31 at 18:18 +0100, pl...@pi... wrote:
> Hi,
> 
> I have a number of gnuplot scripts that have various options set. I 
> would like to set a default value in the script and optionally determine 
> the value from the calling script or command.
> 
> This does not seem to be possible.
> 
> eg.
> 
> if (doPNG) { set terminal png; set output pngfile}
> else { set terminal wxt }
> 
> plot ....
> 
> 
> called as :
> 
> (echo 'doPNG=1;'  && cat cos_fit.gnu) | gnuplot
> 
> 
> Some kind of  isdefined() function would be a solution or simply if the 
> interpreter could return some kind of NaN value that could then be 
> tested instead of triggering an error and breaking out.
> 
> Alternatively kind of error trapping mechanism but that may be going 
> beyond what is needed for this simple test.
> 
> Do you think this would be a useful feature?
> 
> Regards,. Peter.
> 

It's such a useful feature that it has been implemented already:

if (exists("doPNG")) { # whatever...

Look at "help exists". You'll see that, well, help exists. (Sorry, I
couldn't resist...)

There is also "defined", but that's deprecated.

Péter Juhász