edit:
BTW if $| is really at risk of clashing with a variable you defined... something else is wrong. :)
Compare that with the shell, where names like IFS can do unimaginable things if you don't know about them and set them by mistake. (Or maliciously; it's imported directly from the environment, and stuff like this is why shell scripts can basically never be given untrusted input, whereas perl, with the 'taint' option, can.)
Reflecting on all this it's pretty sad that newbies in 2020 are encouraged to learn bash, and continue creating arcane, unreadable, booby-trap-laden scripts in it, all the while looking down their nose at perl.
In Perl, you learn pretty early that single character non-alphanumeric variables ($|, $_, @_ $@) are special and if you encounter them and don't know them, look them up. You also learn that $1 through $9 and $a and $b have special uses, so don't use those without knowing what you're doing either.
> utterly confounding the first time one accidentally runs into it.
Yeah, but every language has some of those. Who remembers "Unexpected T_PAAMAYIM_NEKUDOTAYIM" in PHP? Or giant template error messages in C++? Or just plain segfaults? All paradigms and the languages within them have their own trade-offs and gotchas, and part of learning the language is learning those.
[0] https://stackoverflow.com/questions/26127617/what-exactly-ar...