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# IT441 Network Services Administration PowerPoint PPT Presentation

IT441 Network Services Administration. Prof. Alfred J Bird, Ph.D., NBCT abird@cs.umb.edu http://it441-f12.wikispaces.umb.edu/ Office – Wheatly 2nd floor 096-03 Office Hours – MW 3:00PM to 4:00PM. Comment Blocks. Perl normally treats lines beginning with a # as a comment.

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Prof. Alfred J Bird, Ph.D., NBCT

abird@cs.umb.edu

http://it441-f12.wikispaces.umb.edu/

Office – Wheatly 2nd floor 096-03

Office Hours – MW 3:00PM to 4:00PM

### Comment Blocks

• Perl normally treats lines beginning with a # as a comment.

• Put a comment block at the beginning of your code which includes your name, the name of the module, date written and the purpose of the code.

### Alternative String Delimiters

• q// single quoted string

• qq// double quoted string

• In qq// the // can be replaced with any other non-alphanumeric character provided you use the same character on both ends of the string

### Operators on Strings and Numbers

• \$a = “123”

• \$b = “456”

• What do we get if we write this line of code,

• print \$a + \$b;

• print \$a . \$b;

• ### Math Operators

• ** Exponentiation

• -Unitary Negation

• * Multiplication

• /Division

• %Modulo (Remainder)

• -Subtraction

### What is an Algorithm

• In mathematics and computer science, an algorithm is an effective method expressed as a finite list of well-defined instructions for calculating a function. Algorithms are used for calculation, data processing, and automated reasoning. In simple words an algorithm is a step-by-step procedure for calculations.

### File Operations

• To use a file we need to attach a filehandle to it.

• We do this using the open statement.

• A simple example:

• open (OUT1, “>testoutout.txt”);

• If we open it we want to close it after we are done:

• close (OUT1);

• By convention a filehandle is codded in all capital letters

### A better way

• We want to know for sure that we were successful opening the file so we include a test:

• open (OUT1, “>>test.txt”) or die \$!;

### Using a filehandle

• To use a filehandle you wrap it in angle brackets.

• print <OUT1> “Hello World!\n”;

• chomp (\$in = <IN1>);

### I/O Redirectors

• Remember what the redirectors do:

• >

• >>

• <

### Three problems to code

• Calculate the first 50 prime numbers and write them to an output file.

• Calculate the first 40 members of the Fibonacci Series and write them to an output file.

• Read the two output files and print them to the screen.

### Next Time

• Read pages 179 to 185 in the Perl book

• Complete the four programs