Re: [Gnuplot-info] Managing long/complicated plot commands?

[Bjorn B. <bjo...@gm...>]

Haha, I do my best! Thanks for investigating, fixing, and suggesting a
workaround. I'm looking forward to gnuplot 6.0.5/6.1. :)

On Tue, Mar 31, 2026 at 1:23 AM Ethan Merritt <eam...@gm...> wrote:
>
>
>
> On Mon, Mar 30, 2026 at 12:22 AM Bjorn Buckwalter <bjo...@gm...> wrote:
>>
>> Thanks Ethan for digging to the bottom of this and for the workaround! (I guess that the other workaround is simply to not use `\` and have very long lines, at the expense of readability, of course.)
>>
>> Note that I still see the second problem that I mentioned at the end of an earlier email. I repeat it here. This is the message I get if I include your "junk" code prior to my script. As expected the data files are not found, but the strange thing is the last message:
>>
>> ```
>> reference a string of length  6144
>> garbage
>> "$plot_polar" line 13: warning: Cannot find or open file "world_110m.txt"
>> "$plot_polar" line 13: warning: Cannot find or open file "data/ReportA.txt"
>> "$plot_polar" line 13: warning: Cannot find or open file "data/ReportA.txt"
>> "$plot_polar" line 13: undefined variable: orbit
>> ```
>>
>> I have had trouble where this last message/error pops up sometimes and I haven't been able to nail down the exact circumstances. I believe in this case that it refers to `title orbit`. If I change that to `notitle` it disappears. And changing from `notitle` to `title orbit` in the preceding line does not trigger the message. This seems also somehow related to the length of the command.
>>
>> Many thanks,
>> Bjorn
>
>
> You have a talent for finding bugs.
> I have filed this one on the bug tracker
>        https://sourceforge.net/p/gnuplot/bugs/2865/
> It contains a 1-line example that triggers the bug.
>
> I think you can get this error message only if (a) the previous plot did not find any points to plot
> and (b) the current plot gives no explicit title.
>
> You can avoid this error message in your particular script by adding a title to the line that plots 0
>         for [orbit in orbits] \
>      'data/Report'.orbit.'.txt' using (lon($7)):($3 == 2030 ? filter_lat($6) : NaN) \
>        lc rgb next_color(n) title orbit, \
>    0 title "0", \
> ^^^^^^^^^^^^^^^
>
> Why?  The plot that found no points had already stored a function to generate what
> would have been the title.  But then it never plotted anything and neither evaluated nor
> cleared that function afterwards.  So then if the _next_ plot doesn't provide a title of its
> own it inherits the function to generate one.  In this case that generated title, which would
> have been wrong in any case, references a variable that is no longer in scope.
> The bug will be easy to fix in the code, but the work-around is also easy
>  -- give the following plot a title.
>
>  Ethan