Script to set an HTTP proxy if it is accessible on the network

proxy.sh

#!/usr/bin/env bash

PROXY_AUTH=user:password
PROXY_HOST=proxy.example.com
PROXY_PORT=:80
PROXY_EXCLUDE=".example.com,localhost,127.0.0.1/32,10.0.0.0/8"

# First, remove any existing proxy definitions in /etc/yum.conf
if [ -w /etc/yum.conf ]; then
  sed -i "/^proxy=.*/d" /etc/yum.conf
fi

if [ -n "${PROXY_HOST}" ]; then

# Check to see if we can ping the defined proxy host
  ping -q -c 1 $PROXY_HOST > /dev/null 2>&1
  if [ $? -eq 0 ]; then

# We can, so set the environment variable and Yum configuration

    if [ -n "${PROXY_AUTH}" ]; then
      http_proxy="http://$PROXY_AUTH@$PROXY_HOST$PROXY_PORT"
    else
      http_proxy="http://$PROXY_HOST$PROXY_PORT"
    fi

    https_proxy=$http_proxy
    no_proxy=$PROXY_EXCLUDE
    export http_proxy https_proxy no_proxy
    if [ -w /etc/yum.conf ]; then
      echo proxy=$http_proxy >> /etc/yum.conf
    fi
    echo Set proxy to $http_proxy
  else

# We cannot, so unset the environment variable
    unset http_proxy
  fi
fi