Enable, disable or show current HDDs' write cache setting.

hdd_writecache.sh

#!/usr/bin/env bash
#-----------------------------------------------------------
# Enable, disable or show current HDDs' write cache setting
# https://gist.github.com/007revad
#
# Run in a shell with:
# sudo hdd_writecache.sh
#-----------------------------------------------------------

# If Linux has more than 26 HDDs it names the extra ones sdaa, sdab, sdac etc
# https://rwmj.wordpress.com/2011/01/09/how-are-linux-drives-named-beyond-drive-26-devsdz/
set a b c d e f g h i j k l m n o p q r s t u v w x y z aa ab

echo "To enable write cache on all HDDs type: enable"
echo "To disable write cache on all HDDs type: disable"
echo "Anything else will show the current setting for each HDD."
read -r Action

case "$Action" in
	disable)
		# Disable write caching on all HDDs
		while [[ $1 ]]
		do
			if [[ -e /dev/sd$1 ]]; then
				#sudo hdparm -W 0 /dev/sd$1
				hdparm -W 0 /dev/sd$1
			fi
			shift
		done
		;;
	enable)
		# Enable write caching on all HDDs
		while [[ $1 ]]
		do
			if [[ -e /dev/sd$1 ]]; then
				#hdparm -W 1 /dev/sd$1
				hdparm -W 1 /dev/sd$1
			fi
			shift
		done
		;;
	*)
		# Show the write cache status of all HDDs
		while [[ $1 ]]
		do
			if [[ -e /dev/sd$1 ]]; then
				printf "sd$1 "
				#sudo hdparm -i /dev/sd$1 | grep -Po 'WriteCache=.*abled'
				hdparm -i /dev/sd$1 | grep -o 'WriteCache=.*abled'
			fi
			shift
		done
		;;
esac
echo  # just to keep the shell output consistent

exit