How do I get the last non-empty line of a file using tail in Bash?

Question

How do I get the last non-empty line using tail under Bash shell?

For example, my_file.txt looks like this:

hello

Answer 1

Print the last non-empty line that does not contain only tabs and spaces like this:

tac my_file.txt | grep -m 1 '[^[:blank:]]'

Note that Grep supports POSIX character class [:blank:] even if it is not documented in its manual page until 2020-01-01.

File may contain other non-visible characters, so maybe using [:space:] may be better in some cases. All space is not covered even by that, see here.