Also to be fair, a modern Perl app doesn't even need to use `$|++` since the framework, even if it's raw Plack, will manage output flushing for you since you're no longer banging on raw stdout. I'd say Perl suffers from an even worse problem of legacy tutorials than PHP, but the size of PHP's userbase and thus sheer number of bad tutorials makes it worse there.
chromatic's https://modernperlbooks.com site is nearly unmaintained now, but still contains some good links to tutorials and whatnot on the obvious subject. Including a pretty recent retrospective: https://outspeaking.com/words-of-technology/why-perl-didnt-w...