title: How to use tr command on a string in linux?
body: <p>I am trying to use <code>tr</code> command on a string inside a text file so that I can replace it with a new line character. For example i have a line like this in my file</p>
  
  <pre><code>biological_process      GO:0000001      mitochondrion inheritance       is_a    GO:0048308      organelle inheritance
  </code></pre>
  
  <p>Now I want to convert that to like this</p>
  
  <pre><code>biological_process      GO:0000001      mitochondrion inheritance
  GO:0048308      organelle inheritance
  </code></pre>
  
  <p>I have used <code>tr</code> command before and I thought it would work it but it did now when I try to run it like this</p>
  
  <pre><code>test="biological_process      GO:0000001      mitochondrion inheritance       is_a    GO:0048308      organelle inheritance"
  echo $test | tr 'is_a' '\n'
  b
  olog
  c
  l
  proce
  
   GO:0000001 m
  tochondr
  on 
  nher
  t
  nce 
  
   GO:0048308 org
  nelle 
  nher
  t
  nce
  </code></pre>