Script to merge .part files from Amazon S3

merge-s3-parts.sh

#!/usr/bin/env bash

if [[ $# -ne 1 ]]; then
	echo "Merge matching *.part files in a directory"
	echo
	echo "usage: $0 <directory>"
	exit 1
fi

DIRECTORY="$1"

FILES=$(find "${DIRECTORY}" -regextype sed -regex '.*part[[:digit:]]\+$' | sed 's/\.part[[:digit:]]\+$//' | uniq)

while read -r BASE; do
	COUNT="$(\ls -l "${BASE}".part* | wc -l)"
	MAX="$((COUNT-1))"

	echo "Merging ${COUNT} parts with base ${BASE}"

	# We know there are COUNT parts which belong to this BASE
	# Use `seq` to create an array of consecutive filenames
	# to preserve ordering and prevent whitespace issues.
	IFS=$'\n' PARTS=($(seq -f "${BASE}.part%g" 0 ${MAX}))

	stat "${PARTS[@]}" >/dev/null 2>&1
	if [[ $? -ne 0 ]]; then
		echo "Error: Missing part for file ${BASE}" 1>&2
		exit 1
	fi

	cat "${PARTS[@]}" > "${BASE}"
done <<< "$FILES"