JPGtojpg - regex used by sed command

JPGtojpg.sh

#!/bin/sh

# regular expression syntax used by the sed command (this syntax is described in more detail in “Regular Expressions Unfettered”)

for i in *.JPG ; do
    mv "$i" "$(echo $i | sed 's/\.JPG$/.x/')"
    mv "$(echo $i | sed 's/\.JPG$/.x/')" "$(echo $i | sed 's/\.JPG$/.jpg/')"
done