• The ? variable has the exit/return value of the last program that ran.

if [ $? -eq 0 ]; then
  echo "All is well."
  exit 0
elif [ $? -eq 1 ]; then 
  echo "Doh!"
  exit 1
else
 echo "Really?!"
 exit 2
fi

if [$? -eq 0]; then echo "Error"; else echo "OK"; fi