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unset SSH_AGENT_PID SSH_ENV_REFRESH

[ -r ~/.ssh/env ] && . ~/.ssh/env
[ -n "$SSH_AGENT_PID" ]  || {
   killall ssh-agent
   # No env file (or it's badly corrupted:
   eval $(ssh-agent 2>/dev/null) &> /dev/null
   printenv | grep "^SSH_A"
   SSH_ENV_REFRESH=1
   }

# Ping the agent process:
kill -0 "$SSH_AGENT_PID" >& /dev/null || {
   # No process, so start a new one:
   killall ssh-agent
   eval $(ssh-agent 2>/dev/null) &> /dev/null
   printenv | grep "^SSH_A"
   SSH_ENV_REFRESH=1
   }

ssh-add -l &> /dev/null
[ "$?" -gt 1 ] && {
   # Process alive but unable to be contacted
   # for some reason (wedged/defunct process,
   # or damaged/corrupt UNIX domain socket node?)

   # So kill it:
   kill "$SSH_AGENT_PID" >& /dev/null
   # ... with extreme prejudice if necessary:
   kill -0 "$SSH_AGENT_PID" >& /dev/null \
   || kill -9 "$SSH_AGENT_PID" >& /dev/null

   # ... and start a new one
   eval $(ssh-agent &>/dev/null) &> /dev/null
   SSH_ENV_REFRESH=1
   }

[ -z "$SSH_ENV_REFRESH" ] || {
   # Over-write old env file:
   printenv | grep "^SSH_A" > ~/.ssh/env
   # Append export command:
   echo "export SSH_AGENT_PID SSH_AUTH_SOCK" >> ~/.ssh/env

   # Load the (null-passphrase) identites into the agent:
   ssh-add  < /dev/null &> /dev/null
   }