Gnuplot: What is the difference between plot '/dev/stdin' and plot '-'?

Question

When I use '-' to plot in gnuplot from a pipeline, as follows^⭐:

$ seq 5 | gnuplot -e "plot '-' w lp; pause 99"

it works fine, I can adjust the plot's window size, can show/hide grid without any problem.

But when I use '/dev/stdin' as follows:

$ seq 5 | gnuplot -e "plot '/dev/stdin' w lp; pause 99"

It shows the plot but when I click to maximize the window, it crashes:

line 0: warning: Skipping data file with no valid points

plot '/dev/stdin' w lp
                      ^
line 0: x range is invalid

Could you please explain why does this happen? what is the difference between '-' and '/dev/stdin'?

---

_{⭐ I am deliberately using pause instead of using -p option, because the latter doesn't allow interaction with the plot (no update after resize, can't show/hide grid from the toolbar,etc.)
👉️ I am using bash version 5.0.17 on Ubuntu 20.04, gnuplot 5.2 patchlevel 8, if that info is needed.}

Answer 1

'-' is recognized as a special case, as part of which the refresh command is substituted for replot wherever possible. This means that the program reuses data previously read rather than trying to reread data from the previous source. Also note that '-' means "the current input stream", which is not necessarily stdin.

'/dev/stdin' on the other hand just looks like a normal filename to gnuplot, so a "replot" command tries to read from it again. That would work only if you fed the in the same data a second time. In an interactive session the program prompts you to do so.

As to why you and someone else see different behavior for the -persist mode, I'd have to know a lot more about what you both tried. Note that different terminals implement the persist mode differently. From the documentation:

Depending on the terminal type, some mousing operations may still be possible
in the persistent window.  However operations like zoom/unzoom  that require
redrawing the plot are not possible because the main program has exited.
If you want to leave a plot window open and fully mouseable after creating
the plot, for example when running gnuplot from a script file rather than
interactively, see `pause mouse close`.