Script for working with macOS icns files

VolumeIconUtil.sh

#!/bin/bash
# joevt May 1, 2023

alias icns2icns=/Volumes/Work/Programming/XcodeProjects/Icons/osxiconutils/joevt-osxiconutils/DerivedData/osxiconutils/Build/Products/Debug/icns2icns
alias icns2image=/Volumes/Work/Programming/XcodeProjects/Icons/osxiconutils/joevt-osxiconutils/DerivedData/osxiconutils/Build/Products/Debug/icns2image
alias image2icns=/Volumes/Work/Programming/XcodeProjects/Icons/osxiconutils/joevt-osxiconutils/DerivedData/osxiconutils/Build/Products/Debug/image2icns

patmatch () {
	# substitute for [[ =~ ]] for Mac OS X 10.4
	perl -0777 -ne '<>; exit !( $_ =~ /'"$1"'/ )'
}

dumpicnslist () {
	local theicon="$1"
	local dumps="$2"
	local filelen="$3"
	local pos="$4"

	while (( $pos < $filelen )); do
		local datapos=0
		local datalen=0
		local header=""

		local blob="$(xxd -s $pos -l 32 -p -c 32 "$theicon")"
		local datatypehex="${blob:0:8}"
		local datatype="$(printf "\x${blob:0:2}\x${blob:2:2}\x${blob:4:2}\x${blob:6:2}")"

		printf "%08X" "$pos" # because Mac OS X 10.4.11 xxd doesn't support -o option
		if ((pos == 0)) && [[ $datatypehex = $'\x89PNG' ]]; then
			((datapos = pos))
			((datalen = filelen - pos))
			datatype="PNG"
			header="${blob:0:24}"
			printf "${blob}" | xxd -r -p | xxd -g 4 -l 32 -c 32 | sed -E 's/^[^:]*//'
		else
			datalen="$((0x${blob:8:8}))"
			if ((datalen < 8)); then
				datalen=8
			fi
			blob="${blob:0:$datalen*2}"
			local header="${blob:16:24}"
			
			((datapos=pos+8))
			((datalen-=8))

			printf "%s" "$posstring"
			if [[ $datatype = "TOC " ]]; then
				printf "${blob:0:16}" | xxd -r -p | xxd -g 4 -l 32 -c 32 | sed -E 's/^[^:]*//'
				xxd -g 4 -s $datapos -l $datalen -c 32 "$theicon" | sed "s/^/ /"
				echo
#			lang=C elif [[ $datatype =~ $'icns|slct|sbtp|drop|odrp|open|over|tile|\xFD\xD9\x2F\xA8' ]]; then # not compatible with 10.4.11
			elif lang=C patmatch 'icns|slct|sbtp|drop|odrp|open|over|tile|\xFD\xD9\x2F\xA8' <<< "$datatype" ; then # compatible with 10.4.11
				printf "${blob:0:16}" | xxd -r -p | xxd -g 4 -l 32 -c 32 | sed -E 's/^[^:]*//'
				dumpicnslist "$theicon" "${dumps}" $((datapos+datalen)) $datapos
			else
				printf "${blob}" | xxd -r -p | xxd -g 4 -l 32 -c 32 | sed -E 's/^[^:]*//'
			fi
		fi
		
		if [[ -n $dumps ]]; then
			case $header in
				89504e470d0a1a0a*)
					dd "if=$theicon" bs=1 skip=$datapos count=$datalen "of=${dumps}_$(printf "%06x" $pos)_${datatype}.png" 2> /dev/null
					;;
				0000000c6a5020200d0a870a*)
					dd "if=$theicon" bs=1 skip=$datapos count=$datalen "of=${dumps}_$(printf "%06x" $pos)_${datatype}.jp2" 2> /dev/null
					;;
				ff4fff51*)
					dd "if=$theicon" bs=1 skip=$datapos count=$datalen "of=${dumps}_$(printf "%06x" $pos)_${datatype}.j2c" 2> /dev/null
					;;
				62706c6973743030*)
					dd "if=$theicon" bs=1 skip=$datapos count=$datalen "of=${dumps}_$(printf "%06x" $pos)_${datatype}.plist" 2> /dev/null
					;;
			esac
		fi
		#echo
		((pos = datapos + datalen))
	done
}

dumpicns () {
	#1 = icns file
	#2 = prefix for png, jpg, etc. extracts
	dumpicnslist "$1" "$2" $(($(stat -f %z "$1") + 0)) 0
}

makeicon () {
	#1 = source icon suite
	#... = hex offset of each icon in the icon suite that you want to include
	local theicon="$1"
	shift
	local theicondata=""
	while (($#)); do
		theoffset="$1"
		shift
		if [[ "${theoffset}" = "-" ]]; then
			thetype="$1"
			shift
			thesize="$1"
			shift
			theicondata=${theicondata}$(printf "$thetype" | xxd -p)$(printf "%08x" "$thesize")$(xxd -p -l $((thesize - 8)) -c $((thesize - 8)) /dev/random)
		else
			theheader=$(xxd -p -s $((0x$theoffset)) -l 8 "$theicon")
			thesize=$((0x${theheader:8}))
			theicondata=${theicondata}$(xxd -p -s $((0x$theoffset)) -l $thesize -c $thesize "$theicon")
		fi
	done
	printf "69636e73%08x%s" $((${#theicondata} / 2 + 8)) $theicondata | xxd -p -r
}


checkiconcompatibility () {
	#.VolumeIcon.icns requirements:
	#- 10.4: icons in an icns file cannot be 300KB or greater otherwise the icns is not used. 1024x1024 icons are usually too large. Some 512x512 icons are too large (depends on png compressibility).
	#- 10.5: The icns file cannot exceed 1MB-2B otherwise the icns is not used.
	#- 10.6: no limits that I've encountered
	#- 10.7: TOC must be ordered if it exists
	#- 10.8: TOC must be ordered if it exists
	#- 10.9 - 12.2: no limits that I've encountered
	#- Startup Manager on old Macs like my MacPro3,1 require it32 icons (at least for the 128x128 size - I haven't checked what icon types can be used)
	#- rEFInd doesn't do icons that have png or jpeg or ARGB data - it only does the RGB+8 icon types (it32 and it's smaller versions).
	#- I added support for png and ARGB to my RefindPlus fork (plus old 8bit, 4bit, 1bit icons! I tested these by converting all icons in a Mac OS 9
	#  system file and ROM resources into icns files). I don't know where to get a jpeg 2000 library that can be ported to EFI to support icns files that have jpeg 2000 icons.

	local disklist=""
	if [[ -n $1 ]]; then
		disklist="$(getallmounteddisks -d | egrep "$1")"
	else
		disklist="$(getallmounteddisks -d)"
	fi

	local foldernumber="1"
	while [[ -e VolumeIcons"${foldernumber}" ]]; do
		((foldernumber++))
	done
	
	IFS=$'\n'
	for thepart in $(echo "$disklist"); do
		local themount="${thepart#*:}"
		local thedevice="${thepart%:*}"
		local thevolume="$(basename "$themount")"
	
		local theicon="$themount/.VolumeIcon.icns"
		echo "#•••••$theicon"
		if [[ -f "$theicon" ]]; then
			local thecount=""
			while [[ -d "VolumeIcons${foldernumber}/$thevolume$thecount" ]]; do
				((thecount++))
			done
			local thedir="VolumeIcons${foldernumber}/$thevolume$thecount"
			mkdir -p "$thedir"
			local theprefix="$thedir/$thevolume"
			cp -p "${theicon}" "$theprefix.icns"
			icns2icns "${theprefix}.icns" "${theprefix}_after.icns" || echo "### Error icns2icns"
			dumpicns "${theprefix}.icns" > "${theprefix}.txt" || echo "### Error dumpicns"
			dumpicns "${theprefix}_after.icns" > "${theprefix}_after.txt" || echo "### Error dumpicns2"

			it32=1
			grep it32 "${theprefix}.txt" > /dev/null || it32=0

			if (( it32 )); then
				echo "# Found it32 at icon at $thepart"
				local toccontents="$(perl -ne 'while (<>) {if ((/^.{8}: 544f4320.*/ .. /^$/) && /^ /) { s/^ .{8}:(( \w{8})+).*\n/\1/; s/ (.{8}) .{8}/\1 /g; print "$_"; } } ' < "${theprefix}.txt")"
				if [[ -n $toccontents ]]; then # has a TOC
					local tocexpected="$(perl -ne 'while (<>) {if (!/^00000000/ && !/^\w{8}: 544f4320/ && !/^ / && !/^$/) { s/\w{8}: (\w{8}).*\n/\1/; print "$_ "; } } ' < "${theprefix}.txt")"
					if [[ $toccontents != $tocexpected ]]; then
						echo "#TOC was not sorted"
						echo 'cp -p "'"${theprefix}_after.icns"'" "'"$theicon"'"'
					fi
				fi
				if [[ "$(getvolumeproperty "$thedevice" FilesystemType)" != "apfs" ]]; then
					# we only need to worry about icon sizes in partitions that are viewable in old macOS versions which are unable to mount apfs partitions
					IFS=$'\n'
					local iconoffset=""
					local iconsize=""
					local icontype=""
					local includedicons=""
					local excludedicons=0
					local totalsize=0
					local includedsizes=0
					for theline in $(sed -nE '/^([0-9A-Fa-f]+): .{8} (.{8}) .{53}  (....).*/s//iconoffset=\1;iconsize=$((0x\2));icontype="\3"/p' "${theprefix}.txt"); do
						eval "$theline"
						if [[ $icontype = "icns" ]]; then
							totalsize=iconsize
						elif [[ $icontype != "icns" ]] && (( $iconsize >= 307200 )); then
							echo "#icon at $iconoffset is too large"
							((excludedicons++))
						elif [[ $icontype != 'TOC ' ]]; then
							includedicons="${includedicons} ${iconoffset}"
							((includedsizes += iconsize))
						fi
					done

					if (( $totalsize > 1048574 )); then
						printf "#icon file is too large by %x bytes" $(($totalsize - 1048574))
						if (( $includedsizes > 1048574 )); then
							if (( $includedsizes == $totalsize )); then
								printf "\n"
							else
								printf " or %x bytes after remaking the icon\n" $(($includedsizes - 1048574))
							fi
						else
							printf " but remaking the icon is sufficient\n"
						fi
						((excludedicons++))
					fi
				
					if ((excludedicons)); then
						echo 'bbedit "'"${theprefix}.txt"'"'
						echo 'makeicon "'"${theprefix}.icns"'"'"${includedicons}"' > "'"${theprefix}_reduced.icns"'"'
						echo 'cp -p "'"${theprefix}_reduced.icns"'" "'"$theicon"'"'
					fi
				fi
			else
				it32after=1
				grep it32 "${theprefix}_after.txt" > /dev/null || it32after=0
				if (( it32after )); then
					echo "#it32 added"
					echo 'cp -p "'"${theprefix}_after.icns"'" "'"$theicon"'"'
				else
					echo "#it32 didn't get added - try explicitly adding it"
					icns2image "${theprefix}.icns" "${theprefix}.tiff" || echo "### Error icns2image"
					image2icns "${theprefix}.tiff" "${theprefix}_after2.icns" || echo "### Error image2icns"
					dumpicns "${theprefix}_after2.icns" > "${theprefix}_after2.txt" || echo "### Error dumpicns2"
					echo 'cp -p "'"${theprefix}_after2.icns"'" "'"$theicon"'"'
				fi
			fi
		else
			echo "# No icon at $thepart"
		fi
	done 2>&1
}

Download

curl -L https://gist.github.com/joevt/9fa524ebbef3db46842f14f33cf64ca5/raw -o ~/Downloads/VolumeIconUtil.sh
curl -L https://gist.github.com/joevt/6d7a0ede45106345a39bdfa0ac10ffd6/raw -o ~/Downloads/DiskUtil.sh

You may need to get osxiconutils and update the aliases in the VolumeIconUtil.sh script for some features.

Install (temporarily, only for the current terminal window)

source ~/Downloads/VolumeIconUtil.sh
source ~/Downloads/DiskUtil.sh

Test

# Dump the list of icons in the Volume Icon of the root volume:
dumpicns /.VolumeIcon.icns

# Same as above and extract any png, jp2, or plist items into files with the prefix "macOS_" and list the results:
dumpicns /.VolumeIcon.icns macOS
ls macOS_*

# Make an icon using items (specified by hex offset) from the Volume Icon of the root volume and check the results:
makeicon /.VolumeIcon.icns 0000CBAF 0001CD57 > NewIcon.icns
dumpicns NewIcon.icns

# Mount all partitions and check the compatibility of all Volume Icons of all mounted disk partitions:
# - Icons are copied to a new VolumeIcon folder - the source Volume Icons are unchanged.
# - A new icon is created in the VolumeIcon folder with the items sorted. It will have a TOC and a it32.
# - If the new icon has changes then a command is output that can be used to replace the source Volume Icon.
# - The command will exclude items that are 300 KiB or larger (for Mac OS X 10.4 compatibility).
# - You may want to exclude other items to make the Volume Icon file less than 1 MiB (for Mac OS X 10.5 compatibility).
mountEFIpartitions 
mountPrebootPartitions
mountRecoveryPartitions
mountRecoveryHDpartitions 
checkiconcompatibility

Changes
May 1, 2023

• dumpicns no longer reports syntax error when given a path to an icon file that doesn't exist.
• checkiconcompatibility now accepts a path to a single disk for when you don't want to check all disks.

In Mojave I get:

dumpicns /.VolumeIcon.icns
stat: /.VolumeIcon.icns: stat: No such file or directory
-bash: ((: 0 <  : syntax error: operand expected (error token is " ")
G5s-Mac-Pro:osxiconutils g5$ dumpicns /.VolumeIcon.icns macOS
stat: /.VolumeIcon.icns: stat: No such file or directory
-bash: ((: 0 <  : syntax error: operand expected (error token is " ")
G5s-Mac-Pro:osxiconutils g5$ mountPrebootPartitions
Password:
G5s-Mac-Pro:osxiconutils g5$ mountRecoveryPartitions
G5s-Mac-Pro:osxiconutils g5$ mountRecoveryHDpartitions
G5s-Mac-Pro:osxiconutils g5$ checkiconcompatibility
#•••••/Volumes/Monterey - Data/.VolumeIcon.icns
# No icon at disk4s1:/Volumes/Monterey - Data
#•••••/Volumes/Preboot/.VolumeIcon.icns
# No icon at disk4s2:/Volumes/Preboot
#•••••/Volumes/Recovery/.VolumeIcon.icns
# No icon at disk4s3:/Volumes/Recovery
#•••••/Volumes/Update/.VolumeIcon.icns
# No icon at disk4s5:/Volumes/Update
#•••••/Volumes/High Sierra/.VolumeIcon.icns
# No icon at disk5s1:/Volumes/High Sierra
#•••••/Volumes/Preboot1/.VolumeIcon.icns
# No icon at disk5s2:/Volumes/Preboot1
#•••••/Volumes/Recovery1/.VolumeIcon.icns
# No icon at disk5s3:/Volumes/Recovery1
#•••••/Volumes/WDC1TB/.VolumeIcon.icns
# No icon at disk6s2:/Volumes/WDC1TB
#•••••//.VolumeIcon.icns
# No icon at disk7s2:/
#•••••/Volumes/HFS+/.VolumeIcon.icns
# No icon at disk8s2:/Volumes/HFS+
#•••••/Volumes/BOOTCAMP/.VolumeIcon.icns
# No icon at disk8s3:/Volumes/BOOTCAMP
#•••••/Volumes/Backup/.VolumeIcon.icns
# No icon at disk8s4:/Volumes/Backup
#•••••/Volumes/Mavericks/.VolumeIcon.icns
# No icon at disk9s2:/Volumes/Mavericks
#•••••/Volumes/Recovery HD/.VolumeIcon.icns
# No icon at disk9s3:/Volumes/Recovery HD
G5s-Mac-Pro:osxiconutils g5$ dumpicns /.VolumeIcon.icns
stat: /.VolumeIcon.icns: stat: No such file or directory
-bash: ((: 0 <  : syntax error: operand expected (error token is " ")

• Made a small fix so you should only see the stat: No such file or directory error when you pass a path to a icon file that doesn't exist. You won't see the syntax error message that is caused by the non-existing icon file.
• Changed checkiconcompatibility so that it will accept a path to a single disk for when you don't want to check all disks.