old_contents: #! /usr/local/python
  
  # Print From and Subject of messages in $MAIL.
  # Extension to multiple mailboxes and other bells & whistles are left
  # as exercises for the reader.
  
  import sys, posix
  
  # Open mailbox file.  Exits with exception when this fails.
  
  try:
  	mailbox = posix.environ['MAIL']
  except RuntimeError:
  	sys.stderr.write \
  		('Please set environment variable MAIL to your mailbox\n')
  	sys.exit(2)
  
  try:
  	mail = open(mailbox, 'r')
  except RuntimeError:
  	sys.stderr.write('Cannot open mailbox file: ' + mailbox + '\n')
  	sys.exit(2)
  
  while 1:
  	line = mail.readline()
  	if not line: break # EOF
  	if line[:5] == 'From ':
  		# Start of message found
  		print line[:-1],
  		while 1:
  			line = mail.readline()
  			if not line: break # EOF
  			if line == '\n': break # Blank line ends headers
  			if line[:8] == 'Subject:':
  				print `line[9:-1]`,
  		print
  
new_contents: #! /usr/local/python
  
  # Print From and Subject of messages in $MAIL.
  # Extension to multiple mailboxes and other bells & whistles are left
  # as exercises for the reader.
  
  import sys, os
  
  # Open mailbox file.  Exits with exception when this fails.
  
  try:
  	mailbox = os.environ['MAIL']
  except (AttributeError, KeyError):
  	sys.stderr.write('No environment variable $MAIL\n')
  	sys.exit(2)
  
  try:
  	mail = open(mailbox, 'r')
  except RuntimeError:
  	sys.stderr.write('Cannot open mailbox file: ' + mailbox + '\n')
  	sys.exit(2)
  
  while 1:
  	line = mail.readline()
  	if not line: break # EOF
  	if line[:5] == 'From ':
  		# Start of message found
  		print line[:-1],
  		while 1:
  			line = mail.readline()
  			if not line: break # EOF
  			if line == '\n': break # Blank line ends headers
  			if line[:8] == 'Subject:':
  				print `line[9:-1]`,
  		print
  
subject: change posix to os; and change error message