But that is my point. Print the string "-e\n" in a portable way. I can't think of a way. For GNU coreutils you would need to do `echo - -e` but on a complaint echo you would need to do `echo -e`. So maybe it is portable for some strings. But it can't be used for all cases. Even something as simple as outputting a user entered string can't be done because you don't know if it is handled specially.
You can with the POSIXLY_CORRECT environment variable:
$ /bin/echo --version
echo (GNU coreutils) 8.30
Copyright (C) 2018 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <https://gnu.org/licenses/gpl.html>.
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.
Written by Brian Fox and Chet Ramey.
$ POSIXLY_CORRECT=1 /bin/echo -e
-e
Which is why I say relying on `echo` is fine, since its standard. Relying on `echo` to use options is not. That's also why the author is correct that you should use `printf`, because POSIXLY_CORRECT is not set, then you can run into non-standard behavior, like you showed.
