CSCI 553: Networking III Unix Network Programming Spring 2006

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CSCI 553 Networking III Unix Network
ProgrammingSpring 2006

• High Level Scripting Languages
• (Perl Python)

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Why HL Scripting Languages?

• 2 Factors determine time to solution
• How long it takes to write a program (human time)
• How long it takes that program to run (machine
  time)
• Different languages make different tradeoffs
  between programming speed and execution speed.
• Programmers write the same number of lines of
  code per day no matter the language

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Machine Speed vs. Human Speed
Machine Speed
Fortran
C
C
Java
C
Matlab
Shell Scripts
Python
Perl
Human Speed
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High Level Scripting Languages are for

• Solving problems with the least effort
• Gluing together existing pieces (written in
  shell, compiled languages, system commands, etc.)
• Providing better access to system features than
  shell
• Fast prototyping, quick turn around

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Perl

• Practical Extraction Report Language
• Shell scripts not enough and C programs were
  overkill
• Originally targeted at generating reports and
  other text-oriented functions
• Similar syntax to C and shell, elements taken
  from both
• Perl is an interpreted language
• Now a days, probably already available on any
  Unix/Linux box you come across
• If not easily downloadable and installable
  http//www.perl.com

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Perl Basics

• You can run perl interactively, or from a script
  file
• Interactive perl de 0
• File The normal method, make executable and use
  ! syntax in Linux/Unix
• Hello World

dharter_at_nisl labs cat hello.pl !/usr/bin/perl
print Hello world.\n dharter_at_nisl labs
chmod ux hello.pl dharter_at_nisl labs
./hello.pl Hello world.
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Perl Variables, Strings and Integers/Floats

• Variables not explicitly types (unlike C but like
  shell scripts)
• always needed
• i 3
• print i
• All typical mathematical operations are available
• res 1 3 5
• Strings are easy to define and manipulate
• i A . B concatenation operator
• print i, \n

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Perl Arrays

• sign for single value variables, _at_ used to
  declare and reference arrays
• _at_arr (1,2,3,4,5)
• print _at_arr0, \n
• print _at_arr, \n prints all elements no
  spaces

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Associative Arrays

• HL Scripting languages add associative arrays as
  a basic type, like the array
• known as a Hash, or dictionary
• Not in basic C/C and other compiled languages
• Is in the java language as a Dictionary
• Probably the most useful underused basic type

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Perl Associative Arrays

• DBlt23gt month ("January", 1, "February", 2,
  "March", 3)
• DBlt24gt print _at_month'January'
• 1
• DBlt25gt print _at_month'March'
• 3
• DBlt26gt print keys(month)
• FebruaryMarchJanuary
• DBlt27gt _at_monthnames keys(month)
• DBlt29gt print _at_monthnames0
• February
• DBlt30gt print _at_monthnames1
• March

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Perl String Operators

• Concatenation uses .

DBlt31gt firstname "Derek" DBlt32gt lastname
"Harter" DBlt33gt fullname firstname . " " .
lastname DBlt34gt print fullname Derek Harter

• Simple matching operations for string
• search in string
• DBlt37gt print fullname "ere"
• 1
• string substitution
• DBlt38gt fullname s/ere/fsf/
• DBlt39gt print fullname
• Dfsfk Harter

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Perl Control Structures
for ( i 0 i lt 10 i ) print i,
print \n
i 0 if ( i 0 ) print its
true\n else print its false\n
foreach n (1..15) print i, print
\n
while ( i 0) print its true\n
i
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Perl File I/O
while (_at_lineltstdingt) foreach i (_at_line)
print -gt, i
FILE info.dat open (FILE) _at_array
ltFILEgt close (FILE) foreach line (_at_array)
print line
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Perl Functions

• Complicated syntax, looks like bash/Korn functions

sub pounds2dollars EXCHANGE_RATE 1.54
pounds _0 refers to the first parameter
passed to function return (EXCHANGE_RATE
pounds) book 3.0 value of book in
British pounds value pounds2dollars(book) pri
nt Value in dollars value\n
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Python

• (much?) easier to read than Perl
• All of Perls features, but cleaner syntax
• Especially defining functions
• OO support built in from start

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Python Basics

• You can run python interactively or from a script
  file
• Interactive python
• File same as usual, make executable and add
  !/usr/bin/python
• Hello World

• No needed for statement terminator
• Spacing used for level/grouping

dharter_at_nisl labs chmod ux hello.py dharter_at_n
isl labs cat hello.py !/usr/bin/python print
"Hello world.\n" dharter_at_nisl labs
./hello.py Hello world.
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Python Variables, Strings and Integers/Floats

• Variables not explicitly typed (unlike C but like
  shell scripts, same as perl)
• but, no special identifier needed for variable
  names
• i 3
• print i, i
• All typical mathematical operations are available
• gtgtgt res 1 3 5
• gtgtgt print res
• 16
• gtgtgt print 10 2
• 100
• Strings are easy to define and manipulate
• gtgtgt i "Hello" " " "World"
• gtgtgt print i
• Hello World

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Python Arrays

• Again no special syntax to distinguish arrays
• Referred to as general Lists in Python
• A mutable sequence of objects, can grow and
  shrink
• gtgtgt x1,2,3,4,5
• gtgtgt print x0
• 1
• gtgtgt print x
• 1, 2, 3, 4, 5
• gtgtgt print len(x)
• 5
• Slices are easy to do in python
• gtgtgt print x34
• 4
• gtgtgt print x2
• 1, 2

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Python Associative Arrays

• Python fully supports Associative Arrays, usually
  referred to as Dictionaries in the Python
  literature

• gtgtgt month "January" 1, "February" 2,
  "March" 3
• gtgtgt print month
• 'January' 1, 'February' 2, 'March' 3
• gtgtgt print month'January'
• 1
• gtgtgt print month.keys()
• 'January', 'February', 'March'
• gtgtgt monthnames month.keys()
• gtgtgt print monthnames0
• January
• gtgtgt print monthnames1
• February

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Python String Operators

• Concatenation uses

gtgtgt firstname "Derek" gtgtgt lastname
"Harter" gtgtgt fullname firstname " "
lastname gtgtgt print fullname Derek Harter

• Python strings are a class, use methods to find
  and replace

gtgtgt print fullname.find("ere") 1 gtgtgt print
fullname.find("xyz") -1 gtgtgt print
fullname.replace("ere", "fsf") Dfsfk Harter
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Python String Operations

• gtgtgt dir(fullname)
• 'capitalize', 'center', 'count',
  'decode','encode', 'endswith', 'expandtabs',
  'find', 'index', 'isalnum', 'isalpha', 'isdigit',
  'islower', 'isspace', 'istitle', 'isupper',
  'join', 'ljust', 'lower', 'lstrip', 'replace',
  'rfind', 'rindex', 'rjust', 'rstrip', 'split',
  'splitlines', 'startswith', 'strip', 'swapcase',
  'title', 'translate', 'upper', 'zfill'
• gtgtgt import string
• gtgtgt dir(string)
• 'ascii_letters', 'ascii_lowercase',
  'ascii_uppercase', 'atof', 'atof_error', 'atoi',
  'atoi_error', 'atol', 'atol_error', 'capitalize',
  'capwords', 'center', 'count', 'digits',
  'expandtabs', 'find', 'hexdigits',
  'index','index_error', 'join', 'joinfields',
  'letters', 'ljust', 'lower', 'lowercase',
  'lstrip', 'maketrans', 'octdigits', 'printable',
  'punctuation', 'replace', 'rfind', 'rindex',
  'rjust', 'rstrip', 'split', 'splitfields',
  'strip', 'swapcase', 'translate', 'upper',
  'uppercase', 'whitespace', 'zfill'

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Python Control Structures

• Use colon and indentation to show nesting (and no
  terminators)
• Very different from C/C and shell derived
  languages, takes some getting used to.

python dropped the for (i0 ilt10 i) syntax
a 3 if a lt 0 print less elif a 0
print equal else print greater
a 3 while a gt 0 print a a - 1
for x in range(1,15) print x, print \n
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Python File I/O
import fileinput for line in fileinput.input()
print -gt, line
file open("hello.py") lines
fd.readlines() file.close() for line in lines
print -gt, line
import fileinput for line in fileinput.input(info
.dat) print -gt, line
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Python Functions

• Much cleaner than Perl and shell functions
• Uses normal parameter type names to pass in
  values to a function

def pounds2dollars(pounds) EXCHANGE_RATE
1.54 return (EXCHANGE_RATE pounds) book
3.0 value of book in British pounds value
pounds2dollars(book) print Value in dollars
, value, \n
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Python Classes

• Perl does support OO, but it was tacked onto the
  language
• Much cleaner in Python

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class point2d(object) Constructor defines
how to create new objects. def __init__(self)
self.x 0 self.y 0 Get X
coordinate. def getX(self) return self.x
Set X coordinate. def setX(self, newX)
assert newX gt 0 self.x newX Get and
set Y coordinate. def getY(self) return
self.y def setY(self, newY) assert newY gt
0 self.y newY Calculate norm. def
norm(self) return math.sqrt(self.x 2
self.y 2)