Renamimg all files in a folder using the `mv` command

Imagine you've got hundreds or more jpg files in a folder, and you need to rename them all following a simple convention.
For instance, you might want to add '-img' at the end of each file (but before the file extension).

You can do that easily using the good old mv command, looping through each file and renaming it like so:

for file in *.jpg
do
    mv -i "${file}" "${file/.jpg/-img.jpg}";
done