Re: printf '%s\n' "$@" versus <<< redirection

[Greg Wooledge]

On Sun, Feb 19, 2023 at 10:38:22AM +0000, Kerin Millar wrote:
> $ printf 'n\n' | { IFS='\n' read -r vl; declare -p vl; }
> declare -- vl=""

What the hell...?

unicorn:~$ printf 'n\n' | { IFS='\n' read -r vl; declare -p vl; } 
declare -- vl=""
unicorn:~$ printf 'no\n' | { IFS='\n' read -r vl; declare -p vl; } 
declare -- vl="no"
unicorn:~$ printf 'on\n' | { IFS='\n' read -r vl; declare -p vl; } 
declare -- vl="o"
unicorn:~$ printf 'noon\n' | { IFS='\n' read -r vl; declare -p vl; } 
declare -- vl="noon"

What is it doing there?  And why?

Also:

unicorn:~$ bash-2.05b
unicorn:~$ printf 'n\n' | { IFS='\n' read -r vl; declare -p vl; }
declare -- vl="n"
unicorn:~$ printf 'no\n' | { IFS='\n' read -r vl; declare -p vl; }
declare -- vl="no"
unicorn:~$ printf 'on\n' | { IFS='\n' read -r vl; declare -p vl; }
declare -- vl="on"
unicorn:~$ printf 'noon\n' | { IFS='\n' read -r vl; declare -p vl; }
declare -- vl="noon"

THAT one behaves as I would expect.  It looks like the behavior
changes between bash 3.0 and bash 3.1:

bash-3.0:
declare -- vl="n"
declare -- vl="no"
declare -- vl="on"
declare -- vl="noon"

bash-3.1:
declare -- vl=""
declare -- vl="no"
declare -- vl="o"
declare -- vl="noon"

This looks like a bug to me.  Either it strips trailing n's, or it doesn't,
but in no case should it strip the trailing n only when the string is
less then 4 characters long!

unicorn:~$ printf 'non\n' | { IFS='\n' read -r vl; declare -p vl; } 
declare -- vl="non"
unicorn:~$ printf 'bon\n' | { IFS='\n' read -r vl; declare -p vl; } 
declare -- vl="bo"

Utter nonsense.  Someone please explain this.