title: How to use line that read from file in grep command
body: <p>I'm sorry for my poor English, first.
  I want to read a file (tel.txt) that contains many tel numbers (a number per line) and use that line to grep command to search about the specific number in the source file (another file)!</p>
  
  <p>I wrote this code :</p>
  
  <pre><code>dir="/home/mujan/Desktop/data/ADSL_CDR_Text_Parts_A"
  file="$dir/tel.txt"
  datafile="$dir/ADSL_CDR_Like_Tct4_From_960501_to_97501_Part0.txt"
  
  while IFS= read -r line
  do
      current="$line"
      echo `grep -F $current "$datafile" &gt;&gt; output.txt`
  done &lt; $file
  </code></pre>
  
  <p>the tel file sample : </p>
  
  <pre><code>44001547
  44001478
  55421487
  </code></pre>
  
  <p>but that code returns nothing!
  when I declare 'current' variable with literals it works correctly! 
  what happened?!</p>