title: gnuplot macro dollar sign substitution
body: <p>In Gnuplot 4.6.p3, when I call a script that choses which column I should plot from a file, through</p>
  
  <pre><code>call 'FitModes.gnp' 12 "0.95" 1 "-50"
  </code></pre>
  
  <p>with (the trouble part of) 'FitModes.gnp' being :</p>
  
  <pre><code>c(x)= x==1?'using 3:(abs($$5)):6': x==2?'using 3:(abs($$7)):8': x==3?'using 3:(abs($$9)):10':0    
  column = c($2)
  #print to check the value of this variable
  print "column=",column
  
  p "th$0/b$1/m$3/Data_$0-$1-$3.txt" @column t 'Data' w yerrorlines pt 7 lc @cblue
  </code></pre>
  
  <p>which gives me the "Invalid expression" output: </p>
  
  <pre><code> gnuplot&gt; call 'FitModes.gnp' "12" 0.95 1 "-50"
   column=using 3:(abs($5)):6
  
   gnuplot&gt; p "th12/b0.95/m-50/Data_12-0.95--50.txt" using 3:(abs()):6 t 'Data' w yerrorlines pt 7 lc rgbcolor "#0083AB"
  </code></pre>
  
  <p>due to the absence of column number in the <code>abs()</code> function despite the <code>$5</code> being there in the <code>column</code> variable. Any idea why ?</p>