title: grep matched string plus letters before and after
body: <p>I have two files with strings where the strings in <code>fileA</code> matches part of the strings in <code>fileB</code>. Every string is unique and only has 1 match. 
  I would like to match strings in <code>fileA</code> to the strings in <code>fileB</code> and print the match and 10 characters before and after of the match. </p>
  
  <p>Maybe <code>grep -f</code> would work, but how do I get the 10 characters before and after.</p>
  
  <p>FileA</p>
  
  <pre><code>     TGAGGTAGTAGTTTGTACAGTT
       ACTGTACAGGCCACTGCCTTGC
       TGAGGTAGTAGTTTGTGCTGTT
  </code></pre>
  
  <p>FileB</p>
  
  <pre><code>     CCAGGCTGAGGTAGTAGTTTGTACAGTTTGAGGGTCTATGATACCACCCGGTACAGGAGA
       TAACTGTACAGGCCACTGCCTTGCCAGG
  
       CTGGCTGAGGTAGTAGTTTGTGCTGTTGGTCGGGTTGTGACATTGCCCGCTGTGGAGATA
       ACTGCGCAAGCTACTGCCTTGCTAG
  
       GCTTGGGACACATACTTCTTTATATGCCCATATGAACCTGCTAAGCTATGGAATGTAAAG
       AAGTATGTATTTCAGGC
  
       CTGTAGCAGCACATCATGGTTTACATACTACAGTCAAGATGCGAATCATTATTTGCTGCT
       CTAG
  </code></pre>