This is just to help people out. Initially, you have to be root to be able to use the GPIO pins via the command line. So, to get beyond having to be root, here are some tips.
sudo groupadd gpio
sudo usermod -aG gpio user-name
and, then (add these lines to the 99-gpio.rules file):
sudo nano /etc/udev/rules.d/99-gpio.rules
SUBSYSTEM=="gpio", KERNEL=="gpiochip*", ACTION=="add", PROGRAM="/bin/sh -c 'chown root:gpio /sys/class/gpio/export /sys/class/gpio/unexport ; chmod 220 /sys/class/gpio/export /sys/class/gpio/unexport'"
SUBSYSTEM=="gpio", KERNEL=="gpio*", ACTION=="add", PROGRAM="/bin/sh -c 'chown root:gpio /sys%p/active_low /sys%p/direction /sys%p/edge /sys%p/value ; chmod 660 /sys%p/active_low /sys%p/direction /sys%p/edge /sys%p/value'"
Save and reboot. Now, you should be able to do things like (turn an LED on and off on pin 8):
echo 8 > /sys/class/gpio/export
echo out > /sys/class/gpio/gpio8/direction
echo 1 > /sys/class/gpio/gpio8/value
echo 0 > /sys/class/gpio/gpio8/value
echo 8 > /sys/class/gpio/unexport
sudo groupadd gpio
sudo usermod -aG gpio user-name
and, then (add these lines to the 99-gpio.rules file):
sudo nano /etc/udev/rules.d/99-gpio.rules
SUBSYSTEM=="gpio", KERNEL=="gpiochip*", ACTION=="add", PROGRAM="/bin/sh -c 'chown root:gpio /sys/class/gpio/export /sys/class/gpio/unexport ; chmod 220 /sys/class/gpio/export /sys/class/gpio/unexport'"
SUBSYSTEM=="gpio", KERNEL=="gpio*", ACTION=="add", PROGRAM="/bin/sh -c 'chown root:gpio /sys%p/active_low /sys%p/direction /sys%p/edge /sys%p/value ; chmod 660 /sys%p/active_low /sys%p/direction /sys%p/edge /sys%p/value'"
Save and reboot. Now, you should be able to do things like (turn an LED on and off on pin 8):
echo 8 > /sys/class/gpio/export
echo out > /sys/class/gpio/gpio8/direction
echo 1 > /sys/class/gpio/gpio8/value
echo 0 > /sys/class/gpio/gpio8/value
echo 8 > /sys/class/gpio/unexport