pipe plot data to gnuplot script

Question

If you are on a Unix system (i.e. not Windows) you can use '<cat' instead of '-' to read from stdin:

plot '<cat' using ...

Then you can do cat data.txt | gnuplot script.gp. However, in the specific case you mention in your question, with the plot in the for loop, you read the input three times. So sending the data through stdin is not appropriate, since the data will be gone after the first time it is read.

not a direct answer but this is what i use to quickly look at data. it's especially helpful with the cut command

cat data.txt | cut -f2 -d' ' | gnuplot -p -e "plot '<cat'"

What's wrong with using the -e option of gnuplot from shell? You can provide a variable as input, say data.txt, from shell using:

gnuplot -e "filename='data.txt';ofilename='test.png'" plot.gnu

You should be able to call the above command multiple times with different values for "filename" from shell using a for loop.

And then you change your script plot.gnu to:

set terminal png
set output ofilename
plot for[col=2:4] filename using 1:col title columnheader(col) with lines

If you want to plot data coming from a pipe more than once, you need to store it somehow in memory. My preferred way is to use a temporary file in /dev/shm, which exists in most Linux systems and maps to RAM. Just to keep things clean, I set a trap to delete the temporary file at exit.

Example (using your data.txt):

cat data.txt | (cat > /dev/shm/mytempfile && trap 'rm /dev/shm/mytempfile' EXIT && gnuplot -e "set terminal dumb; plot for[col=2:4] '/dev/shm/mytempfile' using 1:col title columnheader(col) with lines")

Result:

12 ++------------+-------------+-------------+-------------+------------**
   +             +             +             +             + Best ****** +
   |                                                        Worst***#### |
10 ++                                              *******Average $$$$$$++
   |                                           ****                      |
   |                                        ***    $$$$               $$$$
 8 ++                                     **     $$    $$        $$$$$  ++
   |                                    **     $$        $$    $$        |
   |                               *****    $$$              $$       ####
 6 ++                          ****       $$ ############# $$    #####  ++
   |                         **         $$ ##             #  ####        |
   |                       **        $$$ ##                ##            |
   |                     **      $$$$  ##                                |
 4 ++         ***********   $$$$$  ####                                 ++
   |     *****  ###################                                      |
   | ****   $$##                                                         |
 2 **    $$$##                                                          ++
   #########                                                             |
   + $$          +             +             +             +             +
 0 $$------------+-------------+-------------+-------------+------------++
   0             2             4             6             8             10

How about using the system() command

set terminal png
set output "test.png"

# read shell input
# the echo prints the variable, which is then piped to gnuplot
fname = system("read filename; echo $filename")

plot for[col=2:4] fname using 1:col title columnheader(col) with lines 

You can call it now with

echo "data.txt" | gnuplot script.gp