title: Bracket missing error in simple bash line?
body: <p>The following 2 lines in my bash script:</p>
  
  <pre><code>fail_str=$'Checking...\nChecking...'
  if [ tail -1 /home/pi/video_buffer_usage.txt | grep '100% full' ] || [ tail -2 $out_file | grep "$fail_str" ] ; then
  </code></pre>
  
  <p>Give the errors:</p>
  
  <pre><code>./joi_main.sh: line 63: [: missing `]'
  grep: ]: No such file or directory
  </code></pre>
  
  <p>What is wrong with them?</p>