A bash script to make filenames created on Mac/Linux compatible with Windows for shared Dropbox folders (or similar file syncing services).

dropbox-filenames-fix

#!/bin/bash
set -e
#shopt -s compat32

# illegal on windows
re_ctrl='[:cntrl:]'
re_ctrl="^([^$re_ctrl]*)[$re_ctrl]+(.*)"
re_punct='<>:"\\/|?*'
re_punct="^([^$re_punct]*)[$re_punct]+(.*)"
re_ts_td='[. ]+$'
# here be dragons!
re_win='^(CO(N|M[1-9])|PRN|AUX|NUL|LPT[1-9])(\.[^.]+)?$'
# not illegal but quite problematic
re_ls='^ +(.*)'
re_cs='  +(.*)'
re_tsf=' ((\.[^.[:space:]]+)+)$'

punct_replacement='-'
startpoint=()
list=0 # only used to check for conflicts
rename=0
show_new=0
helpme=0
badopts=0
while getopts ':hnlp:r' opt; do
	case $opt in
		h)
			helpme=1
			;;
		n)
			show_new=1
			;;
		l)
			list=1
			;;
		p)
			punct_replacement="$OPTARG"
			if [[ "$punct_replacement" =~ $re_ctrl || "$punct_replacement" =~ $re_punct ]]; then
				badopts=1
				>&2 echo -n 'Invalid punctuation replacement character: '; >&2 printf '%q\n' "$punct_replacement"
			fi

			;;
		r)
			rename=1
			;;
		:)
			badopts=1
			case $OPTARG in
				p)
					>&2 echo "You did not specify any punctuation replacement after the '-$OPTARG' option."
					;;
				*)
					>&2 echo "Argument missing from option '-$OPTARG'."
					;;
			esac
			;;
		\?)
			badopts=1
			>&2 echo "Unknown option '-$OPTARG'."
			;;
	esac
done
if (( OPTIND > 1 )); then
	shift $(( OPTIND - 1 ))
fi
case $(( list + rename )) in
	0)
		helpme=1
		;;
	1)
		if [[ $# -eq 0 ]]; then
			badopts=1
			>&2 echo You must specify at least one directory or file as a starting point.
			>&2 echo Use a dot for the current directory.
		else
			startpoint=("$@")
			for path in "${startpoint[@]}"; do
				if [[ ! -e "$path" ]]; then
					badopts=1
					>&2 printf '%q ' "$path"; >&2 echo is inaccessible or does not exist.
				fi
			done
		fi
		;;
	2)
		badopts=1
		>&2 echo Can either output a list of files, or rename them, not both.
		;;
esac

if (( badopts + helpme )); then
	if (( badopts )); then
		helpout=2
	else
		helpout=1
	fi
	>&$helpout cat <<-EOT
		Usage:
		  $0 [ -h ]
		  $0 -l [ -p PUNCT ] [ -n ] START_POINT [ START_POINT ... ]
		  $0 -r [ -p PUNCT ] START_POINT [ START_POINT ... ]

		Options:
		  -h  This help text (the default).
		  -l  List problematic files.
		  -n  Show suggested new names as well.
		  -r  Rename problematic files.
		  -p  Override dash character used for replacing illegal punctuation.
		EOT
	exit $badopts
fi


if (( rename )); then
	>&2 echo Will prompt for renames. Ensure you only rename items BELOW the main Dropbox directory,
	>&2 echo and do not change your account name directory. Press Ctrl + C to cancel.
else
	>&2 echo Will list problematic filenames.
	>&2 echo 'To perform renames, add the "-r" option before the starting point(s).'
	>&2 echo
fi

suggest () {
	suggested="$1"
	local original="$suggested" es=0
	# order of replacements is significant
	while [[ "$suggested" =~ $re_ctrl ]]; do
		suggested="${BASH_REMATCH[1]} ${BASH_REMATCH[2]}"
	done
	while [[ "$suggested" =~ $re_punct ]]; do
		suggested="${BASH_REMATCH[1]}$punct_replacement${BASH_REMATCH[2]}"
	done
	if [[ "$suggested" =~ $re_ls ]]; then
		suggested="${BASH_REMATCH[1]}"
	fi
	if [[ "$suggested" =~ $re_ts_td ]]; then
		before_end=$(( ${#suggested} - ${#BASH_REMATCH[0]} ))
		suggested="${suggested:0:before_end}"
	fi
	while [[ "$suggested" =~ $re_cs ]]; do
		before_end=$(( ${#suggested} - ${#BASH_REMATCH[0]} ))
		suggested="${suggested:0:before_end} ${BASH_REMATCH[1]}"
	done
	while [[ "$suggested" =~ $re_tsf ]]; do
		before_end=$(( ${#suggested} - ${#BASH_REMATCH[0]} ))
		suggested="${suggested:0:before_end}${BASH_REMATCH[1]}"
	done
	# "${reserved@Q}" and "${reserved^^}" not avail.
	reserved="$(printf '%sX\n' "$suggested" | tr '[a-z]' '[A-Z]')"
	reserved="${reserved%X}"
	if [[ "$reserved" =~ $re_win ]]; then
		suggested="_$suggested"
		es=33
	elif [[ -z "$suggested" ]]; then
		es=22
	elif [[ "$suggested" != "$original" ]]; then
		es=11
	fi
	set +e # don't halt on custom errors
	return $es
}

re_skip='[?][[:space:]]*$'
skipped=0

while IFS= read -r -d $'\0' path <&3; do
	if [[ ! -e "$path" && ! -L "$path" ]]; then
		>&2 echo "'$path' is inaccessible or no longer exists."
		exit 1
	fi
	parent="$(dirname "$path"; err=$?; echo X; exit $err)"
	parent="${parent%?X}"
	current="$(basename "$path"; err=$?; echo X; exit $err)"
	current="${current%?X}"
	if [[ "$current" == . || "$current" == .. ]]; then
		continue
	fi
	suggest "$current"
	suggest_error=$?
	set -e
	if ! (( suggest_error )); then
		# already compliant
		continue
	fi
	if ! (( rename )); then
		if (( show_new )); then
			echo "$path"$'\t'"$parent/$suggested"
		else
			echo "$path"
		fi
		continue
	fi
	first_suggested="$suggested"
	while : ; do
		>&2 echo
		if [[ "$parent" == . ]]; then
			in=
		else
			in=" in '$parent'"
		fi
		if (( suggest_error == 33 )); then
			>&2 echo "'$reserved' is a reserved filename on Windows, so can never be used."
		fi
		>&2 echo "Confirm or adjust sanitised name for '$current'$in."
		>&2 echo "To skip past this rename, type a ? at the end."
		read -r -e -i "$suggested" -p 'New name: '
		confirmed="$REPLY"
		if [[ "$confirmed" =~ $re_skip ]]; then
			(( skipped++ )) || true
			>&2 echo Skipping.
			break
		fi
		suggest "$confirmed"
		suggest_error=$?
		set -e
		case $suggest_error in
			0)
				path_new="$parent/$suggested"
				if [[ -e "$path_new" ]]; then
					>&2 echo Something with that name already exists.
				else
					mv "$path" "$path_new"
					break
				fi
				;;
			22)
				if [[ "$confirmed" != "$suggested" ]]; then
					>&2 echo -n 'That name becomes zero length after re-sanitising it. '
				fi
				>&2 echo Names cannot be zero length.
				suggested="$first_suggested"
				;;
			*)
				>&2 echo That adjusted name still does not comply.
				;;
		esac
	done
done 3< <(find -H "${startpoint[@]}" -depth -print0)

symlinks_broke=0
if (( rename )); then
	>&2 echo
	while IFS= read -r -d $'\0' symlink <&3; do
		(( symlinks_broke++ )) || true
		>&2 echo "The target of the symlink '$symlink' no longer exists."
	done 3< <(find -H "${startpoint[@]}" -depth -xtype l -print0)
	if (( symlinks_broke )); then
		>&2 echo
	fi
	>&2 echo Done.
fi

exit $(( ( skipped + symlinks_broke ) > 0 ))

1. Download
2. Make the script executable:

   chmod +x dropbox-filenames-fix
   

3. Run script to provide help:

   ./dropbox-filenames-fix
   

4. Typical usage is something like:

   ./dropbox-filenames-fix -r ~/Dropbox\ \(Your\ Organisation\)/