1. Perl Lecture #1 Scripting Languages Fall 2004

2. Perl Practical Extraction and Report Language -created by Larry Wall -- mid – 1980’s –needed a quick language –didn’t want to resort to C –derivative of sed or awk (interpreted language used on Unix / sed – stream editor.

3. Perl Intro Cont’d fills the gap between C and awk very powerful language / easy to learn used to write small scripting programs as well as larger applications for the web has been used –cgi scripts – run forms etc. also web apps – shopping cart applications makes use of regular expressions – powerful sequence of characters

4. Why Use? Perl is free many Perl ide’s are free – works great integrated in a Unix environment as most version come with Perl / Mod-Perl and Emb Perl Works well in a Windows environment as well CPAN – comprehensive Perl Archive Network

5. #!/usr/bin/perl #Author: Lori N #Description: First program #Date: Today’s Date $string="Top 10"; $number=10.0; print "Number is 10.0 and string is 'Top 10'\n\n"; $add = $number + $string; print "Adding a number and a string: $add\n"; $concatenate = $number. $string; print "Concatenating a number and a string: $concatenate \n"; $add2 = $concatenate + $add; print "Adding the previous two results: $add2 \n\n"; $undefAdd = 10 + $undefNumber; print "Adding 10 to an undefined variable: $undefAdd\n"; print "Printing an undefined variable: $undefVariable(end)\n";

6. $Scalar When we have just one of something we have a scalar –simplest kind of data that Perl Manipulates. –either a number or a string of characters –Perl uses them interchangeably –no need to declare a variable –Perl will figure it out by its usage

7. Numbers int and floating pt numbers Perl computes with double-precision fp values Literal –is not a result of calculation or I/O op – data written directly into the source code –0 –2001 –-4 –also use Octal ( base 8 ), hexadecimal ( base 16)

8. Strings seq of characters they have a literal representation – ‘single quoted’ and “double quoted” Single quoted Literals - ‘string’ - ‘string\’s’ - ‘hello\n’ – no newline

9. Double Quoted Strings -Double quoted Literals --“string” --“string\n” – newline --“string \””

10. String operators: “hello”. “world” = helloworld “hello”. ‘ ‘. “world” = hello world String repetition operator –x – takes its left operand ( a string ) and makes as many concatenated copies as you specify –“string” x 3 -- stringstringstring –5 x 4 -- 5555

11. Automatic Conversions Perl automatically performs conversions between Numbers and Strings. –by the operator used or they way you attempt to use them in your script -- be careful this might not work out logically like you’d like it to

12. Warnings Perl’s Built in Warnings. –Command line – perl –w myfile.pl –Or add it to your code #!/usr/bin/perl –w –use man perldiag to see more useful troubleshooting flags –also see man perllexwarn man page for warnings that can be turned on and off.

13. Scalar Variables variable – all should be familiar – they hold values a scalar variable holds a single scalar value they all begin with $Perl_identifier can’t start with a digit they are also referenced with the leading $

14. Scalar Assignment --assignment  --$income = ‘tolittle’; --$tax_amount = 1000; --$miles = 100; --$distance = $miles * 5; Similar binary operators as C --+=, *=,.= (string concatenator)

15. Output --print “Hello World\n”; --print ( ) --in a series separated by comma’s --print “My income is “, 0 * 10000, “.or null\n”;

16. Interpolation of Scalar variables into Strings $income = “not much”; $expenses = “quite a bit”; $lifesavings = “My income is $income but my expenditures are $expenses”; or $lifesavings = ‘My income is ‘. $income. ‘but my expenditures are ‘. $expenses; Book has table on page 32 – Operator Precedence and Associativity

17. Comparison Operators = > != Strings – eq, ne, lt, gt, le, ge

18. if Control Structure if ( $variable <= $anothervariable) { Print this; } Curly braces are required

19. No Boolean Data Type No Boolean data type – used simple rules: --the undef value --what if you use a scalar value before you give it a value? --Perl gives it a undef value – neither a string or a number --acts like zero – or an empty string --for Boolean process uses simple rules --undef is false --Zero is false – all else true --empty string ‘ ‘ is false – all else true --The one exception – since numbers and strings are equivalent, the string form of zero, ‘0’ has the same value as its numeric form – false

20. User Input --line-input operator --Perl reads the next complete line of text from standard input ( up to the first newline) --uses it as the value of --its string value has a newline character on the end of it : $line = if ($line eq “\n”) { print “That was just a blank line!\n”; }else { print “That line of input was : $line”; }

21. Chomp Operator --works on a variable --variable has to hold a string --if the string ends in a newline – it removes it --take input from -- chomp removes \n and provides us with just the string. One step: chomp($variable = ) --chomps return value is the number of characters removed – 1

22. while Control Structure --same as C++

23. Tutorial: Simple Perl program: #!/usr/bin/perl –w # #Name: Add Name #Date: Today’s Date #Description: first.pl Ask and Display name print “Please enter you name “; $name = ; chomp ($name); print “Your name is $name”;

24. Execute Your Code Has to be executable: chmod 755 first.pl To run two ways: perl first.pl or./first.pl