title: Using nested for loop in gnuplot
body: <p>I am trying to plot a set of graphs to compare the simulation results with the experimental data. The simulation files are in ordered arrangement on 7X7X7 for various parameters. I need to plot all of those files using a nested for loop for each iXjXk file. The files are named thus : fibrilAll_i_j_k.dat</p>
  
  <p>I have already tried some alternatives like using multiple for loop in the same line. But it doesn't seem to work.</p>
  
  <pre><code>set terminal eps size 1200,800
  set output "all.eps"
  set title "{/*2 Alternative rates}"
  set ylabel "{/*2 fibril mass fraction}" offset 1.5,0,0
  set xlabel "{/*2 Time(h)}"
  set key left top
  plot 'experiment.txt' using 1:6 ps 2 pt 5 title "EXP",\
  for [i=1:7] for [j=1:7] for [k=1:7] 'fibrilAll'._i_j_k.'.dat' using 1:2 with lines title 'i,j,k'
  replot
  </code></pre>
  
  <p>I get the following error message:</p>
  
  <p>internal error : STRING operator applied to undefined or non-STRING variable</p>