https://pubs.opengroup.org/onlinepubs/009696899/utilities/ls.html https://pubs.opengroup.org/onlinepubs/009696899/utilities/ls... lists both -p and -1. And whil

https://pubs.opengroup.org/onlinepubs/009696899/utilities/ls.html https://pubs.opengroup.org/onlinepubs/009696899/utilities/ls... lists both -p and -1. And while -p is marked as an XSI extension, both Darwin and all modern BSD distributions implement it.