title: How to use set to change a shell variable?
body: <p>I am using GNU bash, version 4.3.11(1)-release (x86_64-pc-linux-gnu). </p>
  
  <pre><code>$set | grep SHELL
  SHELL=/bin/bash
  SHELLOPTS=braceexpand:emacs:hashall:histexpand:history:interactive-comments:monitor:verbose
  </code></pre>
  
  <p>Now I want to change the value of the SHELL variable to /bin/dash. So I tried</p>
  
  <pre><code>$set SHELL=/bin/dash
  set SHELL=/bin/dash
  $set | grep SHELL
  SHELL=/bin/bash
  SHELLOPTS=braceexpand:emacs:hashall:histexpand:history:interactive-comments:monitor:verbose
  _=SHELL=/bin/dash
  </code></pre>
  
  <p>I also tried several other syntax. But the SHELL variable value just doesn't change. I have two questions:
  1.How to use set to change the SHELL variable
  2.What is _=SHELL=/bin/dash?</p>