[BASH] Rename all files in a folder to numeric counter

#!/bin/bash
# Place this file (rename.sh) in a different directory
# to the one with your files to be renamed.
# Then run this using relative indexing.
# e.g. If rename.sh is in the parent directory of your files
#      then you run ../rename.sh

COUNTER=1
EXT="jpg"
for l in $(ls)
do
        mv $l "$COUNTER.$EXT"
        ((COUNTER = COUNTER + 1))
done
exit 0