Detect whether or not a 24-bit FLAC has been upconverted from a 16-bit FLAC. Courtesy of "skamp" from the Hydrogenaudio Forums: https://hydrogenaud.io/index.php?topic=97746#msg813393

fbit.sh

#!/bin/bash

me="${0##*/}"

if [ -w "$TMPDIR" ]; then
	tdir="$TMPDIR"
elif [ -w '/tmp' ]; then
	tdir='/tmp'
elif [ -w "$HOME" ]; then
	tdir="$HOME"
elif [ -w "$PWD" ]; then
	tdir="$PWD"
else
	echo "$me: error: can't find a writable directory for creating the temporary file" 1>&2 ; exit 1
fi

tf="$( TMPDIR="$tdir" mktemp "${tdir}/${me}.XXXX" 2>/dev/null )"
if [ -z "$tf" ]; then
	echo "$me: error: can't create temporary file" 1>&2 ; exit 1
fi

checkbits ()
{
	local bps abps tbps=0 n=0
	bps="$( metaflac --show-bps "$1" )"
	flac -ac "$1" 2>/dev/null | fgrep 'wasted_bits' | cut -d '=' -f 3 | cut -f 1 > "$tf"
	while read wb; do
		tbps=$(( tbps + ( bps - wb ) ))
		((n++))
	done < "$tf"
	abps=$(( ( ( tbps * 10 / n) + 5 ) / 10 )) # (* 10 + 5) / 10 for proper rounding
	printf "%2u/%2u bits\t%s\n" "$abps" "$bps" "$1"
}

for f in "$@"; do
	case "$f" in
		*.flac) checkbits "$f" ;;
		*) continue ;;
	esac
done

rm -f "$tf"