title: Substring from a file
body: <p>I need to extract coincidence lines from a file with a regular expression:</p>
  
  <p>This is the content of file:</p>
  
  <pre><code>netbios-ns      137/tcp                         # NETBIOS Name Service
  netbios-ns      137/udp
  hkp             11371/tcp                       # OpenPGP HTTP Keyserver
  hkp             11371/udp                       # OpenPGP HTTP Keyserver
  bprd            13720/tcp                       # VERITAS NetBackup
  bprd            13720/udp
  vopied          13783/udp
  </code></pre>
  
  <p>I need to filter using <code>137</code> with <code>grep</code>:</p>
  
  <pre><code>grep -n -e "137" file
  </code></pre>
  
  <p>The output must be: </p>
  
  <pre><code>netbios-ns      137/tcp                         # NETBIOS Name Service
  netbios-ns      137/udp
  </code></pre>