title: undefine a variable in BASH
body: <p>In order to save some time typing same phrase many times, I defined some variables in in BASH (not a bash file, just the command line bash). How careless I was to give a variable wrong name <code>foo1</code> instead of <code>foo</code>. So, I want to undefine <code>foo1</code>.</p>
  <p>I know I can set <code>foo1</code> empty and define <code>foo</code>. By doing this, <code>foo1</code> is still there and may confuse. I cannot use <code>unset</code> to undefine <code>foo1</code> because it is not an environment variable.</p>
  <p><strong>Question</strong>: How to undefine a variable in BASH?</p>