RPI change username

#/bin/bash
[ $UID = 0 ] || exit 1
#if were here we are root, usually, but be root anyway

echo "you are about to regex things, this is generally considered heavy handed and you are advised to take caution. ctrl-c now to quit without doing anything, otherwise press enter to continue."

#pause the script
line

#ok, the real work
read -p 'Enter Username: ' NEWNAME

#rough test to ensure uniqueness
grep $NEWNAME /etc/passwd
[ $? = 1 ] && exit 1

#back the files up to the fat partition so you can copy them over to a flash stick or something and put them back
cp -t /boot /etc/passwd /etc/group /etc/shadow /etc/gshadow

#do the change
for i in {passwd, shadow, group, gshadow, sudoers}; do
sed -i s/pi/$NEWNAME/g /etc/$i
done

#freshen the backups
for i in {passwd, group, shadow, gshadow}; do cp /etc/$i /etc/$i-; done

#I think were done, normally I do the changes by hand in nano and use regexes very sparingly
#it is possible to back up these file first before doing this by copying them to another directory as root
#so if your careful you can use this blunt instrument of a script
#oh, and I added sudoers up their because otherwise your new username wouldn't have root access via the sudo command