#!/bin/sh

# changetrack - Tracks a given URL and, if it's changed since the last
#    visit, emails the new page to the specified address.

sitearchive="/Users/username/scripts/tmp/changetrack"      # change as desired
sendmail="/usr/sbin/sendmail"           # might need to be tweaked!
fromaddr="[email protected]"     # change as desired

if [ $# -ne 2 ] ; then
  echo "Usage: $(basename $0) url email" >&2
  exit 1
fi

if [ ! -d $sitearchive ] ; then
  if ! mkdir $sitearchive ; then
    echo "$(basename $0) failed: couldn't create $sitearchive." >&2
    exit 1
  fi
  chmod 777 $sitearchive        # you might change this for privacy
fi

if [ "$(echo $1 | cut -c1-5)" != "http:" ] ; then
  echo "Please use fully qualified URLs (e.g., start with 'http://')" >&2
  exit 1
fi

fname="$(echo $1 | sed 's/http:\/\///g' | tr '/?&' '...')"
baseurl="$(echo $1 | cut -d/ -f1-3)/"

# Grab a copy of the web page into an archive file. Note that we can
#  track changes by looking just at the content (e.g., '-dump', not
# '-source'), so we can skip any HTML parsing ...

lynx -dump "$1" | uniq > $sitearchive/${fname}.new

if [ -f $sitearchive/$fname ] ; then
  # We've seen this site before, so compare the two with 'diff'
  if diff $sitearchive/$fname $sitearchive/${fname}.new > /dev/null ; then
    echo "Site $1 has changed since our last check."
  else
    rm -f $sitearchive/${fname}.new     # nothing new...
    exit 0                              # no change, we're outta here
  fi
else
  echo "Note: we've never seen this site before."
fi

# For the script to get here, the site must have changed, and we need to send
# the contents of the .new file to the user and replace the original with the
# .new for the next invocation of the script.

( echo "Content-type: text/html"
  echo "From: $fromaddr (Web Site Change Tracker)"
  echo "Subject: Web Site $1 Has Changed"
  echo "To: $2"
  echo ""

  lynx -source $1 | \
    sed -e "s|[sS][rR][cC]=\"|SRC=\"$baseurl|g" \
        -e "s|[hH][rR][eE][fF]=\"|HREF=\"$baseurl|g" \
        -e "s|$baseurl\/http:|http:|g"
) | $sendmail -t

# Update the saved snapshot of the website

mv $sitearchive/${fname}.new $sitearchive/$fname
chmod 777 $sitearchive/$fname

# and we're done.
exit 0

Configuring Postfix to Send Email

If you want to use Postfix on a standalone server, you must configure two settings in /etc/postfix/main.cf. The first is the hostname (myhostname). This should be a real hostname, something that can be found in a reverse DNS lookup against your IP address . The second is your origin (myorigin), which is the domain name from which email appears to originate. This can be the same as your hostname (this is probably the case for small sites). However, if it is not, be sure to specify the correct hostname. For example, here are the settings for a computer named ip192-168-0-1.ri.ri.cox.net with all email originating from that machine appearing to come from [email protected]:

myhostname = ip192-168-0-1.ri.ri.cox.net
    myorigin = cox.net

If your ISP's network is configured to block outgoing SMTP to all but their SMTP server, using your ISP's SMTP server as a relay host may be the only way you can configure postfix to deliver mail.

If you don't have a permanent domain name for your Mac OS X server, we suggest configuring Postfix to use a relay host (most likely your ISP's SMTP server). To configure Postfix to use a relay, add an entry for relayhost in /etc/postfix/main.cf. For example, we use the following setting:

relayhost = smtp.rcn.com

Along the same lines, you should configure Postfix to masquerade as the appropriate host using the myorigin setting in /etc/postfix/main.cf. In the case of the previous example, the origin is oreilly.com (as in [email protected]):

myorigin = rcn.com