That isn’t incorrect, but it’s not as important as people make it out to be. Linux isn’t certified as POSIX-conformant either.
People are way too stuck on POSIX regarding Fish specifically, but in shell scripting, POSIX compliance boils down to “can it run a pure sh script”. Bash is compliant. Zsh is partially compliant and needs to set an option to emulate sh. Fish uses a different syntax and is not compliant; if that is a problem, don’t execute sh scripts in Fish.
POSIX compliance for shell scripts was important in the 80s and 90s when the #! directive wasn’t as commonly implemented and every script might be executed by the user’s $SHELL instead. That is no longer the case as virtually every Unix-like system’s program loader supports #!.















One day time-out. Both of you. If you want to toss shit at each other, take it to Twitter.