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

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Hi Philipp and all,

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
> > > >
> > > > _______________________________________________
> > > > 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
> > >
>
>
>
> --
>
> Philipp K. Janert
> www.janert.me
>
>
> _______________________________________________
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Re: [Gnuplot-info] Managing long/complicated plot commands?

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