Yeah, for commands, the input/output redirections can precede them, but for some reason it doesn't work for builtin constructs like `while`:

    $ < <( echo foo ) while read -r f; do echo "$f"; done
    -bash: syntax error near unexpected token `do'
    $ < <( echo foo ) xargs echo
    foo

    $ bash --version
    GNU bash, version 5.1.4(1)-release (x86_64-apple-darwin20.2.0)

Maybe wrap the loop either with parentheses or braces?

Tried that, but nope :D I'll let you figure this one out once you get near a computer!

Redirection like this doesn't seem to work if it comes first on GNU bash 5.0.17(1)-release.

For documentation purposes, this is the exact thing I tried to run:

    $ < <(echo hi) while read a; do echo "got $a"; done
    -bash: syntax error near unexpected token `do'

    $ while read a; do echo "got $a"; done < <(echo hi)
    got hi

Maybe there is another way...

One way which isn't great, but an option nonetheless… The zsh parser is happy with that form:

    $ zsh -c '< <(echo hi) while read a; do echo "got $a"; done'
    got hi

My position isn't that it is a good reason to switch shells, but if you're using it anyway then it is an option.

I’ve always preferred zsh and, as I’ve slowly adopted nix, I’ve slowly stopped writing bash in favor of zsh

This is not POSIX compliant though.

These days bash and/or zsh are available nearly every place I care about, so I find POSIX compliance to be much less relevant.

No, process substitution must be provided by the kernel/syslibs, it is not feature of bash. For example there is bash on AIX, but process substitution is not possible because the OS do not support it.

ksh93 depends exclusively on the kernel implementation of /dev/fd devices. I just checked `cat <(ls)` a moment ago on both Linux and AIX 7.2--the latter fails in ksh93t+.

Bash uses /dev/fd when available, but also appears to have an internal implementation which silently creates named pipes and cleans them up. In Bash 5.0.18 on AIX, fake process substitution works just fine, in my testing.

Yes, you are right. Bash 5 on AIX 7.2 works with process substitution. Thanks for the advise!