bulk-rename-qsort

#!/bin/bash
set -euo pipefail

fnd=' '; rpl='_'; dir=${1-${PWD}}

[[ ! -d ${dir} || ! -O ${dir} ]] && printf 'error with %q\n' "${dir}" >&2 && exit 1
[[ ${dir:0:1} != '/' ]] && dir=./${dir}
cd -- "${dir}"

function qsort(){
	local i p sml=() lrg=()
	qsort_res=()
	(($#)) || return 0
	p=${1}; shift
	for i; do ((${p%% *} < ${i%% *})) && sml+=("${i}") || lrg+=("${i}"); done
	qsort "${sml[@]}"; sml=("${qsort_res[@]}")
	qsort "${lrg[@]}"; lrg=("${qsort_res[@]}")
	qsort_res=("${sml[@]}" "${p#* }" "${lrg[@]}")
}

shopt -s globstar dotglob nullglob
depth=()
for fd in ./**/*"${fnd}"*; do
	if [[ -d "${fd}" ]]; then
		count=${fd//[^\/]}
		depth+=("${#count} ${fd}")
	elif [[ -f "${fd}" ]]; then
		fname=${fd##*/}
		fpath=${fd%/*}
		newf=${fpath}/${fname//${fnd}/${rpl}}
		[[ -e "${newf}" ]] && printf '%q already exists.. quitting\n' "${newf}" >&2 && exit 1
		mv -- "${fd}" "${newf}"
	fi
done

qsort "${depth[@]}"
declare qsort_res

for d in "${qsort_res[@]}"; do
	dname=${d##*/}
	dpath=${d%/*}
	newd=${dpath}/${dname//${fnd}/${rpl}}
	[[ -e "${newd}" ]] && printf '%q already exists.. quitting\n' "${newd}" >&2 && exit 1
	mv -- "${d}" "${newd}"
done