title: Double Parameter in shell scripting throwing error
body: <p>I am trying to make my scripts more generic and hence trying to pass parameter.
  I have config file which contains variables (which are used in the scripts) and in the scripts ,I am sourcing (source command) the file in another scripts (ksh).</p>
  
  <p>Config file contains:</p>
  
  <pre><code>p2020_m23_ORACLE_USERNAME=sanjeeb
  </code></pre>
  
  <p>Parameter for the script is <code>p2020_m23</code>.</p>
  
  <p>ksh script:</p>
  
  <pre><code>export SOURCE_CD=$1
  export CONFIG_FILE=/user/spanda20/dbconfig.txt
  source $CONFIG_FILE
  
  USERNAME=${${SOURCE_CD}_ORACLE_USERNAME} &lt;&lt; **This throws error** &gt;&gt;
  USERNAME=$p2020_m23_ORACLE_USERNAME  &lt;&lt;&lt; **This gives correct result** &gt;&gt;
  </code></pre>
  
  <p>manual test:</p>
  
  <pre><code>[spanda2 config]$ export SOURCE_CD=p2020_m23
  [spanda2 config]$ export m23_ORACLE_USERNAME=sanjeeb
  [spanda2 config]$ export USERNAME=${${SOURCE_CD}_ORACLE_USERNAME}
  -bash: USERNAME=${${SOURCE_CD}_ORACLE_USERNAME}: bad substitution
  </code></pre>