Something like:
5:hello
2:pi
Maybe with one blank line with no delimiter as a record separator.
All fields on the same line could work, and would be more greppable, but harder to read for humans.
https://en.wikipedia.org/wiki/Hollerith_constant
As soon as DJB pays up:
http://cr.yp.to/proto/netstrings.txt
harder to write too - very easy to get the length wrong, and tiresome to have to count the length
Something like:
5:hello
2:pi
Maybe with one blank line with no delimiter as a record separator.
All fields on the same line could work, and would be more greppable, but harder to read for humans.