Make ssh-agent idempotent

auto-ssh-agent

# Usage: . /path/to/auto-ssh-agent

# Check if exists ssh-agent in current session
if env | grep -q '^SSH'; then
	echo Agent pid $SSH_AGENT_PID;
else

# Cached ssh-agent info is user-specified
_SOURCE_DIR="~/.local/run"
_SOURCE_FILE="${_SOURCE_DIR}/ssh-agent"

mkdir -p "$_SOURCE_DIR"

# if exists cached file
if [ -f "$_SOURCE_FILE" ]; then
  # find the pid in it and find the program in it.
	_SOURCE_FILE_PID=$( tail -1 "${_SOURCE_FILE}" | cut -d " " -f 4 | cut -d ";" -f 1 )
	_PROCESS_PRG=$( ps -elf | awk '$4 == "'${_SOURCE_FILE_PID}'" {print $15}' )

  # if the process is an ssh-agent
	if [ "ssh-agent" = "$_PROCESS_PRG" ]; then
		source "$_SOURCE_FILE"
	else
    # create new ssh-agent and cache it
		eval $( ssh-agent -s | tee "$_SOURCE_FILE" )
	fi

	unset _SOURCE_FILE_PID
	unset _PROCESS_PRG
else
  # create new ssh-agent and cache it
	eval $( ssh-agent -s | tee "$_SOURCE_FILE" )
fi

unset _SOURCE_DIR
unset _SOURCE_FILE

fi