low=0
high=101
while [ $low -lt $(expr $high - 1) ]
do
    guess=$(expr $low "+" $high)
    guess=$(expr $guess "/" 2)
    echo $guess
    echo "Is your number >=$guess or <$guess Enter 'g' or 'l'."
    read input
    if "$input" == "g"
    then
        high=$guess
    elif "$input" == "l"
    then
        low=$guess
    fi

done
echo Your number must be $low

$ sh guess
Is your number >=50 or <50?  Enter 'g' or 'l'.
l
Is your number >=25 or <25?  Enter 'g' or 'l'.
g
Is your number >=37 or <37?  Enter 'g' or 'l'.
l
Is your number >=31 or <31?  Enter 'g' or 'l'.
g
Is your number >=34 or <34?  Enter 'g' or 'l'.
l
Is your number >=32 or <32?  Enter 'g' or 'l'.
g
Is your number >=33 or <33?  Enter 'g' or 'l'.
g
Your number must be 33.
$