ssh-eternal

#!/bin/bash

# ssh-eternal is a poor-man's clone of ssh-forever
# (http://github.com/mattwynne/ssh-forever)
#
# It's purpose is to run this the first time you connect to a
# remote computer with ssh. This script will then copy your public
# key to the remote computers ~/.ssh/authorized_keys file to
# allow subsequent logins to be done without having to remember
# the remote machine's password every time.
#
# This derivative work was rewritten to work entirely in bash and
# similar shells on machines without ruby or rubygems.
#
# Because the logic for this is wrapped in a single function,
# it can be easily added to one's .profile or .aliases file
# without ever needing to be installed
#
# However, to install, chmod +x the file, and place somewhere
# in your executable path, like /usr/local/bin
#
# Licensed under the MIT license: 
# http://www.opensource.org/licenses/mit-license.php

function ssh-eternal() {
  HELP='Usage: ssh-eternal username@yourserver.com [port] [identity_file]'
  LOGIN=$1
  PORT=$2
  ALTKEY=$3
  KEYFILE=~/.ssh/id_rsa.pub

  # print help in absence of any arguments
  if [ $# == 0 ]; then
    echo $HELP
    exit 1
  fi

  # check for port
  if [ $PORT ]; then
    echo "Connecting to ssh on port $PORT"
    ARGS=" -p $PORT"
  else
    ARGS=""
  fi

  # check for public key
  if [ $ALTKEY ]; then
    echo "Using public key file at $ALTKEY"
    KEY=`cat $ALTKEY`
  elif [ -e $KEYFILE ]; then
    echo "Found public key at $KEYFILE"
    KEY=`cat $KEYFILE`
  else
    echo "You do not appear to have a public key."
    echo "I expected to find one at '$KEYFILE'"
    echo -n "Would you like me to generate one [Y/n]"
    read
    if [[ "$REPLY" == "" || "$REPLY" == "y" || "$REPLY" == "Y" ]]; then
      ssh-keygen -t rsa
    else
      echo "Fair enough, I'll be off then."
      echo "You can generate your own by hand by running 'ssh-keygen -t rsa'"
      exit 2
    fi
  fi

  # build key copy command
  echo "Copying your public key to the remote server. Prepare to enter your password for the last time."
  C1="mkdir -p ~/.ssh"
  C2="chmod 700 ~/.ssh"
  C3="touch ~/.ssh/authorized_keys"
  C4="chmod 700 ~/.ssh/authorized_keys"
  C5="echo $KEY >> ~/.ssh/authorized_keys"
  REMOTE_COMMAND="$C1 && $C2 && $C3 && $C4 && $C5"

  # ssh public key to remote server
  `ssh $LOGIN$ARGS "$REMOTE_COMMAND"`

  if [ $? == 0 ]; then
    echo "Success. From now on you can use just plain old 'ssh $LOGIN'. Logging you in.."
    ssh $LOGIN$ARGS
    exit 0
  else
    echo "Unable to log in."
    exit 1
  fi
}

ssh-eternal $1 $2 $3

Much shorter version. No help, error checking etc.
function ssh-copykey() {
cat ~/.ssh/id_rsa.pub | ssh $1 "cat - >> ~/.ssh/authorized_keys"
}