title: How to read a user input (character) as a column name (object name)
body: <p>I have a data set like, </p>
  
  <pre><code>En     Mn    Hours  var1       var2 
  1      1     1      0.1023488  0.6534707 
  1      1     2      0.1254325  0.5423215 
  1      1     3      0.1523245  0.2542354 
  1      2     1      0.1225425  0.2154533 
  1      2     2      0.1452354  0.4521255 
  1      2     3      0.1853324  0.2545545 
  2      1     1      0.1452369  0.2321542 
  2      1     2      0.1241241  0.2525212 
  2      1     3      0.0542232  0.2626214 
  2      2     1      0.8542154  0.2154522 
  2      2     2      0.0215420  0.5245125 
  2      2     3      0.2541254  0.2542512 
  
  var &lt;- as.character(readline('Enter the variable of your choice')) 
  </code></pre>
  
  <p>the var stores the user input 
  Ex: <code>var1</code> </p>
  
  <p>and if I use it in some R commands say <code>cbind</code> or any for that matter, it doesn't work. 
  simple one if <code>a</code> is a dataset <code>a$var</code> doesn't work. 
  Ex: <code>aggregate(cbind(var)~Mn+hours,a, FUN=mean)</code></p>
  
  <p>And I have a <code>var1</code>, <code>var2</code>, <code>var3</code> like some 30 columns and I want to read multiple inputs from the user </p>
  
  <p>like when user is prompted to enter the variable names he enters like 
  <code>var1 var2 var3</code> (space or comma separated it doesn't matter for me) 
  then I need to read them and use them in the R command line to get some result. </p>