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Re: [Gnuplot-info] Managing long/complicated plot commands?
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From: Helmut H. <he...@ha...> - 2026-03-29 23:09:34
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Hi all,
I've encountered similar problems running gnuplot on Win11. It seems
gnuplot does not like blanks after a continuation slash. When having
line breaks right after the slash the problem went away.
Cheers,
--Helmut
On 3/29/2026 2:02 PM, Philipp K. Janert wrote:
> On Sun, 29 Mar 2026 19:25:16 +0200
> Bjorn Buckwalter <bjo...@gm...> wrote:
>
>> Hi Philipp and all,
> Bjorn -
>
> At this point, I really think reproducability
> is key.
>
> Nothing I have seen so far suggests that there
> is a problem with an arbitrary length limitation
> w/in gnuplot. Instead, something seems to be
> wrong in the very complicated command, function,
> variable situation that you maintain.
>
> Two things:
> - Maybe you should go back and try to build up
> your command again from scratch, one bit at a
> time? And notice when and where it starts to
> break?
> - On a more strategic level: my recommendation
> would be to move some, if not most, of the
> data processing OUT of gnuplot, so that you
> have a data file with the actual data that
> you want to plot. In the long run, this will
> probably turn out to be a better workflow.
>
> Best,
>
> Ph.
>
>> So, trying to minimize a bit more, I realized that a key piece of
>> information that was omitted seems to be that the plot command is
>> inside a function block. Below is a case that reproduces the error
>> for me that you could test. I realised that if I take the command out
>> of the function it works properly.
>>
>> By the way I am on macos and `gnuplot --version` says `gnuplot 6.0
>> patchlevel 4`.
>>
>> Here is the case that fails with the error in question. Since it fails
>> early (at least for me) you will not actually need the data files:
>>
>> ```
>> local lon(x) = x
>> local lat(x) = x
>> local filter_lat(x) = x
>> local next_color(x) = "#00FF00"
>> local next_color_t(x, y) = "#00FF00"
>>
>> local lat1 = 0
>>
>> function $plot_polar(orbits) <<EOF
>> plot \
>> 'world_110m.txt' using (lon($1)):(filter_lat($2)) linecolor "gray"
>> notitle , \
>> lat(0) black dt 2 title "Equator" , \
>> lat(66.6) black dt 5 title "Arctic/Antarctic circle", \
>> lat(-66.6) black dt 5 notitle , \
>> for [orbit in orbits] \
>> 'data/Report'.orbit.'.txt' using (lon($7)):(filter_lat($6)) \
>> lc rgb next_color_t(1, 'cc') notitle, \
>> 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, \
>> 1
>> EOF
>>
>> _ = $plot_polar("A")
>> ```
>>
>> The error message:
>>
>> ```
>> plot 'world_110m.txt' using (lon($1)):(filter_lat($2)) linecolor
>> "gray" notitle , lat(0) black dt 2 title "Equator" , lat(66.6)
>> black dt 5 title "Arctic/Antarctic circle", lat(-66.6) black dt 5
>> notitle , for [orbit in orbits] 'data/Report'.orbit.'.txt'
>> using (lon($7)):(filter_lat($6)) lc rgb next_color_t(1, 'cc')
>> notitle, for [orbit in orbits] 'data/Report'.orbit.'.txt' using
>> (lon($7)):($3 == 2030 ? filter_lat($6) : NaN) lc rgb
>> next_color(n) title orbit, 0, \ 1
>>
>>
>>
>>
>>
>>
>> ^
>> "$plot_polar" line 13: invalid character \
>> ```
>>
>> If I change the `linecolor` in the first line of `plot` to `lc`, The
>> error does not occur. If you test, you may instead get:
>>
>> ```
>> "$plot_polar" line 13: warning: Cannot find or open file
>> "world_110m.txt" "$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 ```
>>
>> By the way, the last message is rather curious. I have had trouble
>> where this 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.
>>
>> I guess Hernán's suggestion to generate a “flat” gnuplot script with a
>> non-gnuplot script could allow me to avoid using function blocks. (At
>> least that is how I interpreted the suggestion).
>>
>> Thanks,
>> Bjorn
>>
>>
>> On Sun, Mar 29, 2026 at 2:24 PM Philipp K. Janert <ph...@ja...>
>> wrote:
>>
>>> On Sun, 29 Mar 2026 11:49:01 +0200
>>> Bjorn Buckwalter <bjo...@gm...> wrote:
>>>
>>>> Thanks Jesper and Philpp. Jespers suggestion with variables can
>>>> likely help – I will try it!
>>> It's not so easy for me to reproduce your
>>> problem, because I don't have access to the
>>> data files, etc.
>>>
>>> The cmd does not seem overly long. I still
>>> suspect that there is a problem with one of
>>> the CRs not being properly escaped - such
>>> as having a blank after a backslash, but
>>> before the actual CR. The error msg in your
>>> original email points to that, too.
>>>
>>> I did not dig into the code to see whether
>>> there is an actual limit to the length of
>>> the cmd line. Ethan would know.
>>>
>>> Do you enter the cmd interactively, or do
>>> you have it in a file, which you load?
>>>
>>>> FYI here is an example plot command that fails:
>>>>
>>>> ```
>>>> plot \
>>>> 'world_110m.txt' using (lon($1)):(filter_lat($2)) with lines
>>>> linecolor "gray" notitle , \
>>>> lat(0) with lines black dashtype 2 title "Equator" , \
>>>> lat(66.6) with lines black dashtype 5 title "Arctic/Antarctic
>>>> circle", \ lat(-66.6) with lines black dashtype 5 notitle , \
>>>> for [orbit in orbits] \
>>>> 'data/Report'.orbit.'.txt' using (lon($7)):(filter_lat($6))
>>>> \ with lines linecolor rgb next_color_t(n, 'cc') notitle, \
>>>> for [orbit in orbits] \
>>>> 'data/Report'.orbit.'.txt' using (lon($7)):($3 == 2030 ?
>>>> filter_lat($6) : NaN) \
>>>> with lines linecolor rgb next_color(n) title orbit, \
>>>> lat(lat1) black notitle # edge of plot
>>>> ```
>>>>
>>>> There is A LOT going on there with various custom functions, etc.
>>>> I tried to make a minimal and “dependency-free” example but
>>>> failed to reproduce the behavior. I could maybe try harder.
>>>>
>>>> Here is in any case the error from gnuplot. The command has been
>>>> concatenated at all baskslashes except the last:
>>>>
>>>> ```
>>>> plot 'world_110m.txt' using (lon($1)):(filter_lat($2)) with
>>>> lines linecolor "gray" notitle , lat(0) with lines black
>>>> dashtype 2 title "Equator" , lat(66.6) with lines black
>>>> dashtype 5 title "Arctic/Antarctic circle", lat(-66.6) with
>>>> lines black dashtype 5 notitle , for [orbit in orbits]
>>>> 'data/Report'.orbit.'.txt' using (lon($7)):(filter_lat($6))
>>>> with lines linecolor rgb next_color_t(n, 'cc') notitle, for
>>>> [orbit in orbits] 'data/Report'.orbit.'.txt' using (lon($7)):($3
>>>> == 2030 ? filter_lat($6) : NaN) with lines linecolor rgb
>>>> next_color(n) title orbit, \ lat(lat1) black notitle # edge
>>>> of plot
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>> ^
>>>> "$plot_polar" line 15: invalid character \
>>>> ```
>>>>
>>>> There is nothing wrong with the backslash (no trailing spaces,
>>>> etc.).
>>>>
>>>> If I change it as so (just shortening style definitions) it works:
>>>>
>>>> ```
>>>> set style data lines
>>>> plot \
>>>> 'world_110m.txt' using (lon($1)):(filter_lat($2)) lc "gray"
>>>> notitle , \ lat(0) black dt 2 title "Equator" , \
>>>> lat(66.6) black dt 5 title "Arctic/Antarctic circle", \
>>>> lat(-66.6) black dt 5 notitle , \
>>>> for [orbit in orbits] \
>>>> 'data/Report'.orbit.'.txt' using (lon($7)):(filter_lat($6))
>>>> \ lc rgb next_color_t(n, 'cc') notitle, \
>>>> for [orbit in orbits] \
>>>> 'data/Report'.orbit.'.txt' using (lon($7)):($3 == 2030 ?
>>>> filter_lat($6) : NaN) \
>>>> lc rgb next_color(n) title orbit, \
>>>> lat(lat1) black notitle # edge of plot
>>>> ```
>>>>
>>>> All I did was remove `with lines` (using `set style data lines`
>>>> instead and replace `linecolor` and `dashtype` with `lc` and `dt`,
>>>> respectively. This is why I say it seems to be somehow related to
>>>> the length/number of characters of a command.
>>>>
>>>> Thanks,
>>>> Bjorn
>>>>
>>>>
>>>> On Sun, Mar 29, 2026 at 5:28 AM Philipp K. Janert
>>>> <ph...@ja...> wrote:
>>>>
>>>>> On Sat, 28 Mar 2026 22:13:40 +0100
>>>>> Bjorn Buckwalter <bjo...@gm...> wrote:
>>>>>
>>>>>> HI all,
>>>>> How long (in characters) are the command lines that
>>>>> you are using? Mine frequently run long, and it has
>>>>> never been a problem.
>>>>>
>>>>> Is it possible that you have problems with embedded
>>>>> newlines, or that something goes awry if your command
>>>>> line runs into a new line in your terminal?
>>>>>
>>>>> Best,
>>>>>
>>>>> Ph.
>>>>>
>>>>>> I rather often run into a problem of my plot commands being
>>>>>> too long, typically resulting in a not-very-helpful error
>>>>>> message such as:
>>>>>>
>>>>>> "$plot_polar" line 21: invalid character \
>>>>>>
>>>>>> It took a lot of head scratching to realize the root of the
>>>>>> problem. I assume there are strong reasons for both the
>>>>>> limitation on command length and the poor error message.
>>>>>>
>>>>>> I cannot be the only one running into this problem. The
>>>>>> situation being what it is, what are the rest of you doing to
>>>>>> manage when you run up against this limit? Replacing
>>>>>> `linecolor` with `lc`, etc, will only get me so far and at
>>>>>> the expense of readability.
>>>>>>
>>>>>> Many thanks,
>>>>>> Bjorn
>>>>>>
>>>>>> _______________________________________________
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>>>>>> gnu...@li...
>>>>>> Membership management via:
>>>>>> https://lists.sourceforge.net/lists/listinfo/gnuplot-info
>>>>>
>>>>>
>>>>> --
>>>>>
>>>>> Philipp K. Janert
>>>>> www.janert.me
>>>>>
>>>>>
>>>>> _______________________________________________
>>>>> gnuplot-info mailing list
>>>>> gnu...@li...
>>>>> Membership management via:
>>>>> https://lists.sourceforge.net/lists/listinfo/gnuplot-info
>>>>>
>>>
>>>
>>> --
>>>
>>> Philipp K. Janert
>>> www.janert.me
>>>
>>>
>>> _______________________________________________
>>> gnuplot-info mailing list
>>> gnu...@li...
>>> Membership management via:
>>> https://lists.sourceforge.net/lists/listinfo/gnuplot-info
>>>
>
>
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