title: init program in shell script
body: <p>I'v been trying to understand this code but I couldn't  get the whole of it. I got that 'init' is the first startup process and that this program is used to start or end a particular mentioned service. But what does the 'cat' in the 'kill' do ?And what happens in the system internal when this program is start, stop and restart?</p>
  
  <pre><code>#!/bin/sh
  test -f /usr/sbin/sshd || exit 0
  case "$1" in
  start)
  echo -n "Starting sshd: sshd"
  /usr/sbin/sshd
  echo "."
  ;;
  stop)
  echo -n "Stopping sshd: sshd"
  kill `cat /var/run/sshd.pid`
  echo "."
  ;;
  restart)
  echo -n "Stopping sshd: sshd"
  kill `cat /var/run/sshd.pid`
  echo "."
  echo -n "Starting sshd: sshd"
  /usr/sbin/sshd
  echo "."
  ;;
  *)
  echo "Usage: /etc/init.d/sshd start|stop|restart"
  exit 1
  ;;
  esac
  </code></pre>