• add numbers on the command line
• du on month end dates

• prepend to a file - https://stackoverflow.com/questions/10587615/unix-command-to-prepend-text-to-a-file
• remove leading and trailing spaces - https://unix.stackexchange.com/a/102021/198064
• search for a string and count the number of characters per line - https://unix.stackexchange.com/questions/400650/counting-the-characters-of-each-line-with-wc

date +%Y%m%d_%H%M%S -r $input_file

Used it in | https://github.com/KamarajuKusumanchi/rutils/blob/master/python3/black_on_selected.sh

Found it in | https://stackoverflow.com/questions/16391208/print-a-files-last-modified-date-in-bash