title: Change first line based of a name associated with the filename
body: <p>I have many text files like these File1, File2, and File3. . . File100</p>
  
  <p>Each file have the same header for example</p>
  
  <pre><code>&gt;7:1234-5678
  line 2
  line 3
  .
  .
  </code></pre>
  
  <p>Each file corresponds to an individual, let's say </p>
  
  <pre><code>File1=Juan
  File2=Pedro
  File3=Carlos
  </code></pre>
  
  <p>What I want to do is add the name of each individual to the first line of each file. something like this:</p>
  
  <pre><code>&gt;Juan_7:1234-5678
  line 2
  line 3
  .
  .
  </code></pre>
  
  <p>In other words: 
  I have several text files (File1...File100), I have a keyfile with these filenames and the names (individuals) whom they belongs. I want to put those names (individuals) in the first line of each file. Does it makes more sense now?.</p>
  
  <p>I have tried with the following code but it is probably wrong.</p>
  
  <pre><code>#!/bin/bash
  File1="Juan";   File2="Pedro"; File3="Carlos"
  
  for i in {1..3}; do
   for file in ./*.txt; do
   eval datafile="\$File$i" 
   sed -i -e '1 s/7:/'"$datafile"'_7:/g' ./File"$1".txt
  done
  done
  </code></pre>