change_passwd.sh

for i in `cat user.txt`
do
        user=`echo $i | awk -F ":" '{print $1}'`
        password=`echo $i  | awk -F ":" '{print $2}'`
        echo "Changing password for ${user}"
        echo "${password}" | passwd --stdin ${user}
        if [ $? -eq 0 ]; then
                echo "Password changed for ${user}"
        else
                echo "Failed to change password for ${user}"
        fi
done

user.txt

abhijeet:mysupersecretpasswrd
rahesh:mysecret@123