title: Better string interpolation in R
body: <p>I need to build up long command lines in <code>R</code> and pass them to <code>system()</code>. I find it is very inconvenient to use <code>paste0/paste</code> function, or even <code>sprintf</code> function to build each command line. Is there a simpler way to do like this:</p>
  
  <p>Instead of this hard-to-read-and-too-many-quotes:</p>
  
  <pre><code>cmd &lt;- paste("command", "-a", line$elem1, "-b", line$elem3, "-f", df$Colum5[4])
  </code></pre>
  
  <p>or:</p>
  
  <pre><code>cmd &lt;- sprintf("command -a %s -b %s -f %s", line$elem1, line$elem3, df$Colum5[4])
  </code></pre>
  
  <p>Can I have this:</p>
  
  <pre><code>cmd &lt;- buildcommand("command -a %line$elem1 -b %line$elem3 -f %df$Colum5[4]")
  </code></pre>