Bash script to update file timestamps by filename

# Find files within the current directory which match the filename pattern of "YYYYMMDD..."
# and update their modified timestamp to the filename
#
# Example, a file named "20210405_test_file.jpg" will have its timestamp
# set to 2021 April 5.

find . -type f -regex '\.\/[0-9][0-9][0-9][0-9][0-9][0-9][0-9][0-9].*' | while read i; do
    D=$(echo "$i" | sed 's:./\([0-9][0-9][0-9][0-9][0-9][0-9][0-9][0-9]\).*:\1:')
    touch "$i" -t "${D}0000"
done