All-in-one CLI environment proxy helper

proxy_helper.sh

# Note, the local keyword is not strictly posix compliant but supported in
# most shells.  You can remove them w/o affecting the scripts except those
# variables will still be in scope outside the function, which can cause some
# info leakage unless you clear them (and you'd want to also trap so they'd be
# cleared when the script is interrupted with something like ctl-c etc)

prox="http://proxy.check:8080"
alias proxyon="export http_proxy=$prox && export https_proxy=$prox"
alias proxyoff='unset http_proxy && unset https_proxy'
echo "Turning http(s) proxies on"
proxyon

# investigate function is repeated here for portability but, we
# only define it if investigate isn't already a defined function
if ! type -t investigate &> /dev/null; then
  investigate() {
    local output_prefix='' # could be something like [*]
    local output_sep=": " # could be ", " ": " etc
    for varname in $@; do
      echo -n "${output_prefix}${varname}${output_sep}"
      v='echo $'
      v="${v}$(echo $varname)"
      eval $v
    done
  }
  export -f investigate
fi

# Display the state of the proxy variables
proxystate() {
  local HTTP="off"
  local HTTPS="off"
  local SOCKS="off"
  if export | grep -q http_proxy;then
    HTTP=$http_proxy
  fi
  if export | grep -q https_proxy;then
    HTTPS=$https_proxy
  fi
  if export | grep -q socks_proxy;then
    SOCKS=$socks_proxy
  fi
  echo "[*] Current state of proxy variables"
  investigate HTTP HTTPS SOCKS
}
export -f proxystate

# detect_http_proxy - Returns a HTTP proxy which is available for use

detect_http_proxy() {
  # Author: Lekensteyn <lekensteyn@gmail.com>
  # Modified by:  kernelsmith@kernelsmith.com

  # If desired:
  # Put this file in /etc/apt/detect-http-proxy and create and add the below
  # configuration in /etc/apt/apt.conf.d/30detectproxy
  #    Acquire::http::ProxyAutoDetect "/etc/apt/detect-http-proxy";

  # APT calls this script for each host that should be connected to. Therefore
  # you may see the proxy messages multiple times (LP 814130). If you find this
  # annoying and wish to disable these messages, set show_proxy_messages to 0
  local show_proxy_messages=0

  # one or more proxies can be specified. Note that each will introduce a routing
  # delay and therefore its recommended to put the proxy which is most likely to
  # be available on the top. If no proxy is available, a direct connection will
  # be used
  try_proxies=(
    proxy.check:8080
  )

  print_msg() {
      # \x0d clears the line so [Working] is hidden
      [ "$show_proxy_messages" = 1 ] && printf '\x0d%s\n' "$1" >&2
  }

  active_proxy=""
  # adjust the -w timeout if needed for accuracy
  for proxy in "${try_proxies[@]}"; do
      # if the host machine / proxy is reachable...
      if nc -w 3 -z $(echo ${proxy/:/ }) &> /dev/null; then
          active_proxy="http://$proxy"
          print_msg "Proxy found: $active_proxy"
          echo "$active_proxy"
          break
      fi
  done

  print_msg "No active proxies"

  # Workaround for Launchpad bug 654393 so it works with Debian Squeeze (<0.8.11)
  # not required if not < 0.8.11 or not using this w/APT
  #echo DIRECT
}
export -f detect_http_proxy

active_proxy=$(detect_http_proxy)
http_proxy=$active_proxy
https_proxy=$active_proxy
proxystate