Index

1. step 1: ftpscan

• produce a program to handle all the arguments
• arguments are:
  • -c which counts the number of times a file is accessed
  • -h which displays a simple help line
• two arguments at present
  • could write the argument handling code ourself
  • better solution is to use getopts why?

2. Arguments for ftpscan

• initially let us write the usage and imports:

• #!/usr/bin/python
  
  import sys, getopt
  
  
  def Usage ():
      print "ftp [-c][-h]"
      sys.exit(0)

• now lets collect the arguments:

• try:
      optlist, list = getopt.getopt(sys.argv[1:],
                                    ’:ch’)
  except getopt.GetoptError:
      Usage()
      sys.exit(2)

• now we process the arguments:

• for opt in optlist:
      print opt
      if opt[0] == ’-h’:
          Usage()
      if opt[0] == ’-c’:
          print "c option found"

• remember that getopt consists of two elements:
  • the first is a list of (option, value) pairs
  • the second is the list of program arguments left after the option list was stripped
• consider:

• >>> import getopt
  >>> args = ’-a -b -cfoo -d bar a1 a2’.split()
  >>> args
  [’-a’, ’-b’, ’-cfoo’, ’-d’, ’bar’, ’a1’, ’a2’]
  >>> optlist, args = getopt.getopt(args, ’abc:d:’)
  >>> optlist
  [(’-a’, ’’), (’-b’, ’’), (’-c’, ’foo’), \
   (’-d’, ’bar’)]
  >>> args
  [’a1’, ’a2’]

3. Long arguments

• using long option names is equally easy (although these are not needed for ftpscan!)

• >>> s = ’--condition=foo --testing --output-file \
          abc.def -x a1 a2’
  >>> args = s.split()
  >>> args
  [’--condition=foo’, ’--testing’, ’--output-file’,
    ’abc.def’, ’-x’, ’a1’, ’a2’]
  >>> optlist, args = getopt.getopt(args, ’x’, [
  ...  ’condition=’, ’output-file=’, ’testing’])
  >>> optlist
  [(’--condition’, ’foo’), (’--testing’, ’’),
   (’--output-file’, ’abc.def’), (’-x’, ’’)]
  >>> args
  [’a1’, ’a2’]

4. Step 2: ftpscan

• make the python program read the ftp log file a line at a time

• #!/usr/bin/python
  
  from sys import argv
  
  def scanner(name, function):
      file = open(name, ’r’)
      line = file.readline()
      while line:
          function(line)
          line = file.readline()
      file.close()
  
  def processLine(line):
      print line
  
  
  filename = ’ftplog.data’
  scanner(filename, processLine)

• you will also need to download this test data file ftplog.data.
• notice that this snippet of code is extremely useful :-)
• it provides a scanner function which scans a file
  • it reads the file a line at a time and
  • then calls the function to operate on each line
• currently it calls processLine
  • which simply prints the line
    

5. ftpscan: step 3

• now alter the program to cut the line into date, client machine, file
  • display these component strings
    • think split
• here is a line (which is broken into several to fit the slide):

• Mon Nov 18 17:38:24 2002 1 \
  g410-helpdesk.isd.glam.ac.uk 51200 \
  /user/ftp/pub/m2/osi/lab1.tar b _ o a \
  IEUser@ ftp 0 * c

• using split write some code which prints the date, client machine, file

• #!/usr/bin/python
  
  import string
  
  def processLine(line):
      words=string.split(line)
      print "date = ", words[:5]
      print "machine = ", words[-7]
      print "file = ", words[-5]
  
  
  processLine("Mon Nov 18 17:38:24 2002 1 \
               g410-helpdesk.isd.glam.ac.uk \
               51200 \
               /user/ftp/pub/m2/osi/lab1.tar \
               b _ o a")

Index

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