ssh-agent-setup.sh

#!/bin/bash
#
# File: ~/.ssh/ssh-agent-setup
#
# Checks authentication environment.
# If the ssh-agent is not running, starts a new one.
#
# Setup instructions:
#
# 1) For bash and ksh users:
#
#    Include the following in your ~/.bashrc or ~/.kshrc:
#
#    . $HOME/.ssh/ssh-agent-setup
#
#    Note, The common error is to instead include this command to ~/.bash_profile file.
#    The authentication method of any subsequent non-login shell sessions
#    started will not be supplied by the running ssh-agent which
#    only calls ~/.bashrc for their shell session setup. The startup
#    of the login shell session includes a call to ~/.bashrc anyway.
#
#
#
# 2) For csh and tcsh users:
#
#    Include the following in your ~/.cshrc or ~/.tcshrc
#
#    source $HOME/.ssh/ssh-agent-setup
#
#

SSH_ENV=$HOME/.ssh/env-$HOSTNAME
SSH_CONFIG=$HOME/.ssh/config

function ssh_clean {
    d="$HOME/.ssh"

    f0=$d/known_hosts
    f1=$d/known_hosts_tmp

    cat /dev/null > $f1

    while read host line; do
  if [ $host != "localhost" ]; then
      echo $host $line >> $f1

    mv $f1 $f0

    chmod 600 $f0
}


# Initialize new agent and add authentication
function start_agent {

    echo "Initialising new SSH agent..."

    # Start authenticating daemon
    # No authentications set up yet, just starting daemon!
    ssh-agent | head -2 > ${SSH_ENV}
    chmod 600 ${SSH_ENV}

    # Find SSH_AUTH_SOCK and SSH_AGENT_PID of the available daemon
    . ${SSH_ENV} > /dev/null

    # Add authentication to this and only this daemon
    ssh-add
}

# Setup SSH Agent forwarding
function ssh_enable_forward {

    grep -q ^ForwardAgent $SSH_CONFIG &> /dev/null
    local forward_enabled=$?
    if [[ ! -f $SSH_CONFIG || $forward_enabled -ne 0 ]]; then
            echo "Enabling SSH Agent Forwarding..."
            cp $SSH_CONFIG ${SSH_CONFIG}_save
            echo "ForwardAgent yes" > $SSH_CONFIG
            cat ${SSH_CONFIG}_save >> $SSH_CONFIG
            chmod 600 ${SSH_CONFIG}_save
        fi
}

if [ -f "$SSH_ENV" ]; then
    # Find SSH_AUTH_SOCK and SSH_AGENT_PID of the available daemon
    . ${SSH_ENV} > /dev/null

    # Check if the agent is still running
    ierr=0
    ps ${SSH_AGENT_PID} > /dev/null || ierr=1

    if [ $ierr == "0" ]; then
  echo > /dev/null
    else
  # If not initialize new agent and
  # add authentication
  start_agent;
    fi
else
    start_agent;
fi

# Clean localhost entry in the known host file
#ssh_clean
# Enable forwarding
ssh_enable_forward