title: Why isn't "ls $(pwd/cat)" working?
body: <p>in my Ubuntu,for example:</p>
  
  <pre><code>$ pwd
  /home/yangxiaoyu/c/test
  </code></pre>
  
  <p>If I say:</p>
  
  <pre><code>ls /home/yangxiaoyu/c/test/cat
  </code></pre>
  
  <p>I get:</p>
  
  <pre><code>ls: 无法访问'/home/yangxiaoyu/c/test/cat': No such file or directory
  </code></pre>
  
  <p>but, if I say:</p>
  
  <pre><code>ls $(pwd/cat)
  </code></pre>
  
  <p>I get:</p>
  
  <pre><code>bash: pwd/cat: No such file or directory
  0x2b    1.txt  catfile  ff    readFile.c  ~rootfile  yxy.h
  0X2b.c  a.out  example  list  ref.c       thread.c
  </code></pre>
  
  <p>As you can see, when I use <code>$(pwd/cat)</code> as an argument to <code>ls</code> it shows an error output and also the list of items in the current directory.</p>
  
  <p>Why is this happening?</p>