title: Conditional assignment of SHELL variable in Makefile
body: <p>I have a Makefile variables VAR_1 and VAR_2. </p>
  
  <p>I need to assign the value of $($VAR1)_VAR2) to FINAL_VAR, ONLY if $($VAR1)_VAR2) is NOT EQUAL TO /dev/null. If $($VAR1)_VAR2) is EQUAL TO /dev/null then FINAL_VAR should be assigned some default value say "/usr/tmp"</p>