Allow SSH_AUTH_SOCK to roam (use a working agent connection)

permanent_auth_sock_hack.sh

# Following remembers possible agent connections,
# switches to some still open connection if the current one fails,
# and pins SSH_AUTH_SOCK to a fixed location
# such that you never need to worry about breaking connections.
#
# This perhaps is bash only.  Source this in your .bashrc or .bash_aliases
# Currently needs "timeout" installed as well.

# See https://gist.github.com/hilbix/7d3bacb1b91cdf6df5c6
permanent_auth_sock_hack()
{
local auth a

auth="$HOME/.ssh/.agent.sock"

# remember authentication sockets
[ -n "$SSH_AUTH_SOCK" ] &&
[ ".$auth" != ".$SSH_AUTH_SOCK" ] &&
[ -S "$SSH_AUTH_SOCK" ] &&
ln --backup=t -sn "$SSH_AUTH_SOCK" "$auth."

# pin it
export SSH_AUTH_SOCK="$auth"

# choose a working one
timeout 0.3 ssh-add -l >/dev/null ||
for a in "$auth."*
do
        ln -fn "$a" "$auth"
        timeout 2 ssh-add -l >/dev/null 2>/dev/null || { rm -f "$a"; continue; }
        echo "Working connection to authentication agent found." >&2
        break
done
}

permanent_auth_sock_hack