title: Naming the legend entry in Gnuplot, while plotting from a data file
body: <p>I am plotting a data file with six columns in gnuplot. If the plot of column 2 against column 1 is x(t), I want that line in the legend something like <code>x(t)</code>, NOT what I currently get for column two against column one, <code>"trial.dat" u 1:2</code>. </p>
  
  <p>How would I name the legend line, then? </p>