Find Prime Numbers Using Bash Script

This script will determine all prime numbers between two positive integers a and b. a and b are supplied as command line arguments.

if [ $# -ne 2 ]
then
    echo  "Wrong Number of Arguments in the Command Line"
    exit
fi

if [ $1 -le 0 -o $2 -le 0 ]
then
    echo "Either 1st or 2nd Argument is NEGATIVE or ZERO "
    exit
fi
    
a=$1;b=$2
if [ $a -gt $b ]
then 
    t=$a
    a=$b
    b=$t
fi
i=$a
while [ $i -le $b ]
do
    set -- `factor $i | cut -f 2 -d":"`
    if [ $# -eq 1 ]
    then
        echo "$i is a Prime Number"
    fi
    i=`expr $i + 1 `
done

$ sh x.sh 2 50
2 is a Prime Number 
3 is a Prime Number 
5 is a Prime Number 
7 is a Prime Number 
11 is a Prime Number 
13 is a Prime Number 
17 is a Prime Number 
19 is a Prime Number 
23 is a Prime Number 
29 is a Prime Number 
31 is a Prime Number 
37 is a Prime Number 
41 is a Prime Number 
43 is a Prime Number 
47 is a Prime Number