title: Find a 4 digit number and get the text after them
body: <p>i need to extract some numbers from a .sql file name:
  from "TDB_full_335.51_2013_02_14.sql" i only want "2013_02_14"
  i can get this with:</p>
  
  <pre><code>echo $(find -s ~/Downloads | grep -e '\.sql' | awk -F/ '{print $NF}' | sed -n '/TDB_full/p' | awk 'END{print}' | awk '{gsub(".sql", "");print}' | cut -d "_" -f4 -f5 -f6)
  </code></pre>
  
  <p>this is ok for now but if the filename length changes this will fail. is there a way to search for the 4 digits "2013" and get the digits after to ".sql"?</p>
  
  <p>if found this:</p>
  
  <pre><code>grep -o '\([[:digit:]]\)\{4\}'
  </code></pre>
  
  <p>but gives me only "2013"</p>