title: change from julia mode to shell mode
body: <p>I am using Julia 1.4.2. my version info is,</p>
  <p>Julia Version 1.4.2
  Commit 44fa15b150* (2020-05-23 18:35 UTC)
  Platform Info:
  OS: Linux (x86_64-pc-linux-gnu)
  CPU: Intel(R) Core(TM) i5-6200U CPU @ 2.30GHz
  WORD_SIZE: 64
  LIBM: libopenlibm
  LLVM: libLLVM-8.0.1 (ORCJIT, skylake)</p>
  <p>How to change from Julia command mode to Shell mode in julia?</p>
  <p>I want to perform os commands such as <code>ls</code> <code>pwd</code> etc.,</p>