start_sshAgent.sh

#!/bin/bash

# Author: FeldiM2425
# Licence: MIT
# Description:
#   This Bashscript is used to detect the ssh-agent 
#   on a specific Unix-Socket (defined by the SSH_AUTH_SOCK environment variable)
#   and start it when the ssh-agent is not running. If "-f" is passed as argument
#   the socket file will be deleted before the ssh-agent is started even if a ssh-agent
#   was detectet. The agent WILL NOT GET shut down before this operation
#   If "-f" is not passed the script will only delete the socket file when no agent is listening
#   on that socket. In case the socket file is missing, the agent simply gets started.
#
# Usage:
#    $ ./start_sshAgent.sh        ... starts the ssh agent with the given socket file 
#    $ ./start_sshAgent.sh -f     ... force deleting the socket before starting the ssh-agent

FORCE=false

while getopts f opt
do
   case $opt in
       f) FORCE=true;;
   esac
done

# When the socket already exists we might want to delete the socket
if [ -e "$SSH_AUTH_SOCK" ] ; then
	echo "Existing socket detected"
	
	# Check all programs listening on the $SSH_AUTH_SOCK unix-socket
	# When no program is listening it is safe to delete the socket
	if (( $(ss -Hax state listening src $SSH_AUTH_SOCK | wc -l) < 1 ))
	then
		echo "No ssh-agent detected on the socket"
		FORCE=true
	fi

	if [ $FORCE = true ]
	then
		echo "Deleting socket file at \"$SSH_AUTH_SOCK\""
		rm $SSH_AUTH_SOCK
	fi
fi

# When the socket doesn't exist (either by deleting it in this script or it didn't exist)
# the ssh-agent can be started on that socket, otherwise just a information is printed
if [ ! -e "$SSH_AUTH_SOCK" ] ; then
    echo "Start SSH-Agent..."
	ssh-agent -a "$SSH_AUTH_SOCK" >/dev/null
	ssh-add 2>/dev/null >/dev/null # This line adds the ~/.ssh/id_rsa key
else
    echo "Socket file at \"$SSH_AUTH_SOCK\" already exists!"
    echo "Run this script again with -f or delete the socket file first!"
fi

echo "Finished"