Lowerspace: remove spaces and lowercase all files and folders in argument

lowerspace.sh

#!/usr/bin/env bash

##
## lowerspace.sh directory
## Remove spaces and lower case all files and folders in `directory`
##

set -o xtrace
set -o errexit
set -o nounset

die() {
	ret=$?
	printf "%s\n" "$@" >&2
	exit "$ret"
}

ren() {
	local newname
	newname=${1// /_}
	newname=${newname,,}
	echo "$1" "$newname"
	[[ $1 != "$newname" ]] && mv -- "$1" "${newname}"
}

traverse() {
	local file
	cd -- "$1" || exit
	for file in *; do
		[[ -d $file ]] && traverse "$file"
		ren "$file"
	done
	cd .. || exit
}

shopt -s nullglob dotglob

[[ $# -ne 1 ]] && die "Usage: $0 folder_name"

SRC=$1
[[ -d "$"SRC ]] && die "$SRC does not exist"

traverse $SRC