title: store value from data file in variable gnuplot using dummy plot
body: <p>This question is related to this one:
  <a href="https://stackoverflow.com/questions/28987654/store-commented-value-from-data-file-in-gnuplot">store commented value from data file in gnuplot</a></p>
  
  <p>I formatted now every single data file that it looks like:</p>
  
  <pre><code>    1.0  0.01
  
      0.2  0.0163  0.0000125
      0.4  0.0275  0.0001256
  </code></pre>
  
  <p>Then I tried to read the first line and store it into variables in this way:</p>
  
  <pre><code>set term push
  set term unknown    
  plot dataFile every ::0::0 using (a=$0):(b=$1)
  set term pop
  </code></pre>
  
  <p>But this is not working as it should, why? The rest of the file I plot as follows:</p>
  
  <pre><code>plot dataFile every ::1 using 1:2:3 with errorbars lt 1 linecolor "red",f(a,b)
  </code></pre>