Run docker, forwarding your SSH agent into the container

docker-run-ssh.sh

#!/bin/sh

#
# Forwards SSH agent into a Docker container running in the active
# docker-machine
#

PROGNAME=$(basename $0)

NAME=$(docker-machine active)

if test -z "${NAME}"; then
    echo "${PROGNAME}: Must active a docker machine with `eval $(docker-machine env [machine-name])`" >&2
    exit 1
fi

# Setup SSH forwarding into docker host
# From https://gist.github.com/rcoup/53e8dee9f5ea27a51855
SSH_SOCK=docker.${NAME}.$$.ssh.socket

SSH_PORT=$(docker-machine inspect -f '{{.Driver.SSHPort}}' ${NAME})

# Most ssh options copied from docker-machine ssh
# Others:
#  -A - Enables forwarding of the authentication agent connection
#  -M - Places the ssh client into ``master'' mode for connection sharing
#  -S - Specifies the location of a control socket for connection sharing
#  -f - Requests ssh to go to background just before command execution
#  -n - Redirects stdin from /dev/null
#  tail -f /dev/null - command that never ends
ssh -i $HOME/.docker/machine/machines/${NAME}/id_rsa \
    -o PasswordAuthentication=no \
    -o IdentitiesOnly=yes \
    -o StrictHostKeyChecking=no \
    -o UserKnownHostsFile=/dev/null \
    -o LogLevel=quiet \
    -o ConnectionAttempts=3 \
    -o ConnectTimeout=10 \
    -p ${SSH_PORT} \
    docker@localhost \
    -A -M -S $SSH_SOCK -f -n \
    tail -f /dev/null

DM_AGENT_SOCK=$(ssh -S $SSH_SOCK docker@localhost echo \$SSH_AUTH_SOCK)

# Try our best to kill the socket on exit
trap "ssh -S $SSH_SOCK -O exit docker@localhost" EXIT

docker run \
       -v $DM_AGENT_SOCK:/ssh-agent \
       -e "SSH_AUTH_SOCK=/ssh-agent" \
       "$@"