Script to convert directory with photos from iPhone (.HEIC) to .jpg format. Requires libheif-examples package installed. Notice: .jpg output is ~20% larger than .HEIC original.

heif-directory-convert.sh

#!/bin/bash

set -euE

echo "$0 $* [$$] START" >&2

declare DIR="${1:-.}"
declare REMOVE="${2:-no}"

at_least_one_output_exists() {
	set -e
	local filename="$1"
	local noext="${filename%.HEIC}"
	local output
	for output in "$noext.JPG" "$noext.PNG" "$noext.jpg" "$noext.png"; do
		# not -f, empty output may lead to a lose of photo
		if [ -s "$output" ]; then
			echo "SKIP: $filename & $output are both already exist" >&2
			echo "yes"
			return 0
		fi
	done
	echo "no"
	return 0
}

heic2jpg() {
	local filename="$1"
	local output="${filename%.HEIC}.jpg"
	# heif-convert comes from libheif-examples package
	echo START heif-convert "$filename" "$output" >&2
	if ! heif-convert "$filename" "$output"; then
		echo "FAILED $filename -> $output keep original in place"
	elif [ "$REMOVE" = '--remove' ]; then
		rm -vf "$filename"
	fi
	echo DONE  heif-convert "$filename" "$output" >&2
	return 0
}

main() {
	local exists
	find "$DIR" -type f -name "*.HEIC" | sort | while read -r filename; do
		exists="$(at_least_one_output_exists "$filename")"
		[ "$exists" != 'yes' ] && heic2jpg "$filename"
	done
	return 0
}

main "$@"
echo "$0 $* [$$] SUCCESS" >&2
exit 0