title: Remove pattern from string with gsub
body: <p>I am struggling to remove the substring before the underscore in my string.
  I want to use * (wildcard) as the bit before the underscore can vary:</p>
  
  <pre><code>a &lt;- c("foo_5", "bar_7")
  
  a &lt;- gsub("*_", "", a, perl = TRUE)
  </code></pre>
  
  <p>The result should look like:</p>
  
  <pre><code>&gt; a
  [1] 5 7
  </code></pre>
  
  <p>I also tried stuff like "^*<em>" or "?</em>" but did not really work.</p>