Frequency of a Character in a String [Shell Program]

clear

echo "Enter the
String:\c"

read str

echo "Enter the
character:\c"

read ch

n=0

i=`expr
"$str" : ".*"`

while [ $i -ne 0 ]

do

 m=`echo $str|cut -c $i`

 if [ "$m" = "$ch" ];then

 
n=`expr $n + 1`

 fi

 i=`expr $i - 1`

done

echo "The
frequency is :" $n