TDC597 Linuxbased Network Management Lecture Two

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TDC597Linux-based Network ManagementLecture
Two

• James T. Yu, Ph.D.
• jyu_at_cs.depaul.edu
• School of CTI
• DePaul University

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Lecture Outline

• Shell Programming
• Input/Output
• Data Structures
• Control Structures
• Modular Design
• Awk
• Pattern Match
• Associative Array (hashing)

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What is Shell Programming?

• A high-level program writing in a script language
  (called Shell).
• Compiler vs. Interpreter
• No object code
• Simple data structure
• Simple control structure
• Easy to use
• Task automation

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Your First Shell Program
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How to create a shell program

• Write a program using a text editor (such as vi)
• Convention !/bin/sh at the beginning
• Good programming practice
• If it is a shell program, use .sh as the suffix
  of the file
• first.sh
• Add comments in your program (anything after
  is comment.)
• Change the file mode to be executable
• chmod x first.sh
• Run the program
• If the current directory is in PATH, enter
  first.sh
• If the current directory is not in PATH, enter
  ./first.sh
• . means the current directory

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File I/O
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Shell Variables(with the program scope)
X define a variable X reference a
variable X and Y are defined in the program
(variable.sh) but are not defined outside the
program.
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Shell Variables(outside the program scope)
X and Y are also available to other Shell
Programs
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Simple Arithmetic
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Simple Command I/O
Read data from the keyboard The output goes to
the screen.
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Program Structure

• Sequence you already learned it
• Conditions
• comparison and boolean operation
• if
• case
• Loop
• while
• for

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if structure
if ltconditiongt then ltshell commandsgt fi
if ltconditiongt then ltshell commandsgt elif
ltconditiongt then ltshell commandsgt elif
ltconditiongt ltshell commandsgt else ltshell
commandsgt fi
if ltconditiongt then ltshell commandsgt else ltshell
commandsgt fi
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Comparison
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if-condition
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More Comparison
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Shell Command Arguments
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Get Input from Command Line
1 1st parameter 2 2nd parameter
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File Test
-s ltfilegt file exists with size gt 0 -f ltfilegt
file exists
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File Test (cont.)
test ltexpgt same as ltexpgt
-d is it a directory?
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Save Execution to a Variable
The special character (back quote) is to save
the execution result into a variable.
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case
case variable in v1) ltshell commandsgt
v2) ltshell commandsgt ) not required,
but good practice ltshell commandsgt esac
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while structure
while ltconditiongt do ltshell commandsgt done
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while a practical example
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while loop through the command line arguments
number of command arguments
shift move to the next argument
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for structure
for ltvar gt in LIST do ltshell commandsgt done
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function

• Why do we need functions in the program
  structure?
• Software reuse
• modular design

Function Declaration define Function
Invocation call/use it
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a telnet script
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AWKAho, Kernighan, Weinberger
Rule never change the order
It is a programming language for pattern patch
and more
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AWK Program Structure
awk BEGIN statements pattern1
statements pattern2 statements END
statements INPUTDATA
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Awk Program Statements

• Almost the same as C (or Java)
• if
• while
• do

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One-Line Awk Program
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Essential Features

• Automatic Input Separation
• Pattern Match
• String Processing
• Associative Array

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Input Data Separation
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Pattern Match - Regular Expression

• Regular expression ( r )
• Pattern match ltexpressiongt / r /
• Example 6 /tdc511/
• Example 7 /bash/
• Example 6 ! /tdc511/ does not match

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Pattern Match regular expression
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String Processing
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String Processing
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String Processing
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Associative Array

• One of the most powerful features in Awk (and
  also in Perl)
• It is known as hashing in Perl
• In traditional programming language, array index
  must be an integer and must be in sequence
• Associative array use character string as array
  index
• studentIDjohn 1234
• studentGradeMarytdc511 A-

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A non-trivial programCompute the Grade Point
Average
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Awk program
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Homework 2

• Task Automation
• performance test with ping

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Output of ping
Round Trip Delay 0.728 ms Jitter (mdev)
0.328 ms
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One-line script for data collection and
formatting
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Script Prolog
!/bin/sh /home/jyu/tdc597/hw02/hw02script.sh
Author James Yu Date 11/27/06
Description compute the round trip delay with
various packets Usage hw02script.sh ltno
command line argumentsgt
You must have a prolog at the beginning of your
script.