This script completely purges other kernels than the current running. Useful for when you've upgraded to a newer one, it's stable, and you don't need the old one.

purge-other-kernels-than-current.sh

#!/bin/bash
CURRENT_KERNEL=`uname -r`
OLD_KERNELS=`ls /usr/src/ -l | grep -v ">"| awk '{print $9}' | grep linux | grep -v $CURRENT_KERNEL | sed -r 's/^.{6}//'`
AMOUNT_OF_OLD_KERNELS=`ls /usr/src/ -l | grep -v ">" | awk '{print $9}' | grep linux | grep -v $CURRENT_KERNEL | wc -l`
echo "Amount of kernels to get rid of: $AMOUNT_OF_OLD_KERNELS"
for (( COUNTER=0; COUNTER<$AMOUNT_OF_OLD_KERNELS; COUNTER++ ))
do
	HEAD=$((COUNTER+1))
	DIR=`ls /usr/src/ -l | grep -v ">" | awk '{print $9}' | grep linux | grep -v $CURRENT_KERNEL | head -n$HEAD | tail -n1`
	echo -ne "Fetching package name of kernel #$HEAD... "
	# Gentoo only
	PACKAGE=`equery b $DIR | head -n+1`
	echo "done!"
	echo "Kernel #$HEAD is currently known as $PACKAGE"
	echo -ne "Removing kernel #$HEAD ..."
	# Gentoo only
	emerge -Cq $PACKAGE
	echo "done!"
	echo -ne "Removing kernel #$HEAD source directory... "
	rm -rf /usr/src/$DIR
	echo "done!"
	# Truncating the "linux-" from directory name so that we can find it in /boot and /lib/modules
	KERNEL=`echo $DIR | sed -r 's/^.{6}//'`
	echo -ne "Removing kernel #$HEAD from /boot... "
	rm -f /boot/*$KERNEL*
	echo "done!"
	echo -ne "Removing kernel #$HEAD modules... "
	rm -rf /lib/modules/$KERNEL
	echo "done!"
	echo "$PACKAGE has been purged from the system."
done
echo "All your old kernels have been purged. Have a nice day and remember to install Gentoo!"