BASH functions for using the C.H.I.P. GPIO pins.

gpio.sh

#!/bin/bash
#FIXME Add usage() function to improve documentation

# Enable exposure of the specified GPIO pin (0-8)
gpio_enable()
{
  if [[("$1" -lt 0) || ("$1" -gt 8)]] ; then
    echo "Valid pins are 0-8"
    return -1;
  fi
  PIN=$((408 + $1));
  sudo sh -c "echo $PIN > /sys/class/gpio/export"
}
# Disables exposure of the specified GPIO pin (0-8)
gpio_disable()
{
  if [[("$1" -lt 0) || ("$1" -gt 8)]] ; then
    echo "Valid pins are 0-8"
    return -1;
  fi
  PIN=$((408 + $1));
  sudo sh -c "echo $PIN > /sys/class/gpio/unexport"
}
# Sets the pin to input or output mode
gpio_mode()
{
  if [[("$1" -lt 0) || ("$1" -gt 8)]] ; then
    echo "Valid pins are 0-8"
    return -1;
  fi
  PIN=$((408 + $1));
  if [[ ! -d /sys/class/gpio/gpio$PIN ]] ; then
    echo "GPIO$1 has not been enabled yet, please call gpio_enable"
    return -1
  fi
  MODE=""
  if [[("$2" == "in") || ("$2" == "IN")]] ; then
    MODE="in"
  elif [[("$2" == "out") || ("$2" == "OUT")]] ; then
    MODE="out"
  fi
  if [[ "$MODE" == "" ]] ; then
    echo 'Valid modes are "in" or "out"'
    return -1;
  fi
  sudo sh -c "echo $MODE > /sys/class/gpio/gpio$PIN/direction"
}
gpio_write()
{
  if [[("$#" -lt 2)]] ; then
    echo "Usage: gpio_write pin value"
    return -1
  fi
  if [[("$1" -lt 0) || ("$1" -gt 8)]] ; then
    echo "Valid pins are 0-8"
    return -1;
  fi
  PIN=$((408 + $1));
  #FIXME - Accept more than one word
  sudo sh -c "echo $2 > /sys/class/gpio/gpio$PIN/value"
}
gpio_read()
{
  if [[("$1" -lt 0) || ("$1" -gt 8)]] ; then
    echo "Valid pins are 0-8"
    return -1;
  fi
  PIN=$((408 + $1));
  cat /sys/class/gpio/gpio$PIN/value
}

# The MIT License (MIT) Copyright (c) 2016 Jeff Larkin
#
# Permission is hereby granted, free of charge, to any person obtaining a copy
# of this software and associated documentation files (the "Software"), to deal
# in the Software without restriction, including without limitation the rights
# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
# copies of the Software, and to permit persons to whom the Software is
# furnished to do so, subject to the following conditions:
#
# The above copyright notice and this permission notice shall be included in
# all copies or substantial portions of the Software.
#
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
# SOFTWARE.

Even better. You can prepare your base label for current and future kernels.

From docs.getchip.com

Here is a bash script to compute the base (courtesy of bbs user @fordsfords)

LABEL_FILE=grep -l pcf8574a /sys/class/gpio/*/*label BASE_FILE=dirname $LABEL_FILE/base
BASE=cat $BASE_FILE

This is my own version of Jeff's code

Edit: Decided to RTFM and figured out my problem. Thanks for the guide!

sorry.. total noob here but when I try to run the git clone I keep getting

Permission denied (publickey).
fatal: Could not read from remote repository.

Please make sure you have the correct access rights
and the repository exists.

what step did I miss or what am I doing wrong?

check the kernel: "the GPIO expander pins start at 408 on 4.3, 1016 on 4.4.11, and 1013 on 4.4.13-ntc-mlc"
from: https://docs.getchip.com/chip.html#how-you-see-gpio

Aren't there only 8 pins? That would be 0-7 and not 0-8.

See https://docs.getchip.com/images/chip_pinouts.jpg

@gonzalo heads up on something that should affect your copy too.