How to pass parameters to a Bash script?

You use $1, $2 in your script. E.g:

date1="$1"
date2="$2"
sed "s/$date1/$date2/g" wlacd_stat.xml >temp.xml
mv temp.xml wlacd_stat.xml

To iterate over the parameters, you can use this shorthand:

#!/bin/bash
for a
do
    echo $a
done

This form is the same as for a in "$@".