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.

Added back the license that was inadvertently removed in the last commit.

Thanks for writing this Jeff! Unfortunately Gist doesn't let you do pull requests... but just letting you know if you want to copy changes from my fork I also added functions for controlling CSI pins.

I have successfully had this script working. I wanted to go back to it to refresh my memorys but it is no longer working for me. What am I going wrong? I am now getting the following error:

chip@chip:~$ gpio_enable 0
sh: line 0: echo: write error: Invalid argument

On CHIP kernel 4.4, GPIO expander pins start at 1016 not 408 (@cornbreadheadman, it's maybe your problem: changing all 408 by 1016 works for me).
Maybe a bash jedi can check current kernel version and set this first pin number as a variable?

kernel_version=$(uname -r | cut -b 3)

Will store in $kernel_version the third character of "uname -r" (3 or 4, depending on kernel)

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.