init_ssh-agent.sh

# init_ssh-agent.sh
# Ssh agent initialisation script
#
# Description:
#   If there is running an ssh-agent already with your username then $SSH_AGENT_PID en $SSH_AUTH_SOCK will be set to the correct variables.
#   Otherwise this script will run a new ssh-agent and add your id_rsa file to it. And again set the variables needed.
#
# Version:  1.0
# Author:   Dieter Castel
# License:  Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License
#           See: http://creativecommons.org/licenses/by-nc-sa/3.0/ for more info.

# Variables:
#   You can change this paths as you wish but they must remain absolute for ssh-agent.
#   WARNING: before changing the paths consider the remove lines: rm -f "$scriptpath" and rm -f -r "$socket".
#
#   Location of the script that is created when this script first runs.
scriptpath=~/.ssh/set_ssh-agent.sh
#   Socket you want the agent to run on.
socket=~/.ssh-sock
#   Location of the keyfile. Change if you want to use an other keyfile.
keyfile=~/.ssh/id_rsa


echo "Will initialize ssh-agent for following user: $USER"

# Function that will initialize a new ssh agent.
function init_new_ssh_agent {
    echo "No running ssh-agent for your login."
    #No running ssh-agent.
    #Remove old files and directories.
    rm -f "$scriptpath"
    rm -f -r "$socket"
    #Make ssh-agent on the socket and create the script.
    ssh-agent -a "$socket" > "$scriptpath"
    #Run the script to set the environmental variables
    source "$scriptpath"
    #Add the keyfile
    ssh-add "$keyfile"
    #Write protect the file so you don't accidentely remove/change it.
    chmod u-w "$scriptpath"
    echo "ssh-agent (PID = $SSH_AGENT_PID) is ready for use."
}

# Get a list of process ids of ssh-agents.
pidList=`pidof ssh-agent`
# Test if there is one running already.
if pidof ssh-agent; then
#Some agent is already running
    if ssh-add -l | grep "$USER"; then
        #Agent with given login is already up and running.
        echo "ssh-agent (PID = $SSH_AGENT_PID) with your login is already running on socket $SSH_AUTH_SOCK"
        return;
    fi
    #Test if the running ssh-agent has the same PID as our script.
    if [ -e "$scriptpath" ] && [ -e "$socket" ] && source "$scriptpath"; then
        echo "Succesfully ran $scriptpath"
        if ssh-add -l; then
            #Succes the ssh-agent running is functional.
            if ssh-add -l | grep "$USER"; then
                #The key for $login is already added to the ssh-agent.
                echo "ssh-agent (PID = $SSH_AGENT_PID) is ready for use";
            else
                #Adding the keyfile to the agent (prompt for passphrase will show up).
                ssh-add "$keyfile"
                echo "ssh-agent (PID = $SSH_AGENT_PID) is ready for use";
            fi
        fi;
    else
        echo "Failed running $scriptpath ."
        init_new_ssh_agent;
    fi;
else
    init_new_ssh_agent;
fi