Program to find out the area of a existing triangle

echo "Enter three sides of a triangle "
read a b c
if test $a -gt $b  
then
 if test $a -gt $c
 then
  if test  `expr $b + $c` -gt $a
  then
   e=`expr $a + $b + $c`
   s=`expr $e / 2`
   x=`expr $s - $a`
   y=`expr $s - $b`
   z=`expr $s - $c`
   eq=`expr $s \* $x \* $y \* $z`
   area=$(echo "sqrt ($eq)" | bc -l )
   echo "$area is the area of this triangle "
  else
   echo "This is not the sides of a valid triangle. Please, Enter a valid sides"
  fi
 else
  if test  `expr $a + $b` -gt $c
  then
   e=`expr $a + $b + $c`
   s=`expr $e / 2`
   x=`expr $s - $a`
   y=`expr $s - $b`
   z=`expr $s - $c`
   eq=`expr $s \* $x \* $y \* $z`
   area=$(echo "sqrt ($eq)" | bc -l )
   echo "$area is the area of this triangle "
  else
   echo "This is not the sides of a valid triangle. Please, Enter a valid sides"
  fi
 fi
else
 if test $b -gt $c
 then
  if test `expr $a + $c` -gt $b
  then
   e=`expr $a + $b + $c`
   s=`expr $e / 2`
   x=`expr $s - $a`
   y=`expr $s - $b`
   z=`expr $s - $c`
   eq=`expr $s \* $x \* $y \* $z`
   area=$(echo "sqrt ($eq)" | bc -l )
   echo "$area is the area of this triangle "
  else
   echo "This is not the sides of a valid triangle. Please, Enter a valid sides"
  fi
 else
  if test `expr $b + $a` -gt $c
  then
   e=`expr $a + $b + $c`
   s=`expr $e / 2`
   x=`expr $s - $a`
   y=`expr $s - $b`
   z=`expr $s - $c`
   eq=`expr $s \* $x \* $y \* $z`
   area=$(echo "sqrt ($eq)" | bc -l )
   echo "$area is the area of this triangle "
  else
   echo "This is not the sides of a valid triangle. Please, Enter a valid sides"
  fi
 fi
fi