1. print 'Hello world.'; Tren Griffith

2. Outline:  Perl introduction  Scalar Data  Variables  Operators  Control Structures  Input  Lists and Arrays  Comparison Examples

3. Introduction  Unix scripting language.  Developed in 1987 for report (text) processing.  Free under GNU Public License.  TMTOWTDI - “Tim Toady” – Perl’s Motto. There’s more than one way to do it.

4. Scalar Data & Variables Two basic Scalar data types. Numbers ○ Integer or Floating-point. ○ undef = 0 Strings ○ Sequence of Characters. ○ Enclosed in either single or double quotes. ○ undef = Empty string  Each Scalar variable holds a single value.  Names of variables begin with a $ and followed by an identifier. $Employee $Count

5. Features:  Any scalar variable inside a double quoted string, is replaced by its value. Example: ○ $string="world"; print "hello $string \n"; ○ The example will print “hello world” and switch to a new line

6. Features II:  There is automatic conversion between numbers and strings.  Examples: $fred=10; $barney=5;  Print $fred*$barney; #Prints 50. As the * is a arithmetic operator, it multiplies.  Print $fred x $barney; #Prints 1010101010 Since x is a string operator, Perl interrupts this as “10 five times”  Print $fred. $barney; #Prints 105 Since. (dot) is a string operator, Perl interrupts this as “10 and 5”

7. Features III:  Automatic conversion between numbers and strings: In practice. In C++ - If you needed to use an integer as a string… ○ std::string IntToStr( int n ) { std::ostringstream result; result << n; return result.str(); } In Perl – If you need to use an integer as a string… Just use it. No conversion needed.

8. Control Structure  If Statement: if(…){ … }  If Else Statement: if(…){ … } else { … }  While Statement while(…){ … }

9. Control Structure II  While Very Similar to C++, however braces are required in all cases. In C++: ○ while(…) cout << “Hello”; ○ It is legal to omit braces in C++. In Perl: ○ while(…) { $counter++ } ○ Program would fail without the braces.

10. Operators  Assignment Operator: =  Arithmetic Operator: + - * /  String Operator. Concatenation X Repetition  Numeric Comparison: == (Equal) != (Not Equal) <, <= (Less than, less than or equal to) >, >= (Greater than, Greater than or equal)

11. Standard Input  Reads input and outputs if the line was empty or not. $line= ; if($line eq “\n”){ print “Empty line. \n” } else { print “Not empty line. \n” }

12. Standard Input II  Example of Perl’s “There is more than one way to do it” Reads a line, outputs the line, and stops at end of file. ○ More strict version: while(defined($line= )){ print “This line was: $line \n”; } ○ Shortcut version: while( ){ print “This line was: $_ \n”; }

13. Lists and Arrays  Lists are very user friendly in Perl. The sigil of an array(list) is @ (1,2,3,4,5,6,7) # A list of numbers. (1..7) # The exact same list, created by the range operator. ($a..$b) # Range set by variables.  Accessing Lists: Very similar to how you would access a C++ Vector. @numbers=(1..5); print $numbers[0]; #Prints 1 – Lists begin at 0 print $numbers[2]; #Prints 3 print $numbers[5]; #Nothing is printed, value of anything out of range is undef. Print $numbers[$#numbers]; #prints 5, the last element of the list.

14. Lists and Arrays II  Swaps the values of $barney and $fred ($fred, $barney)=($barney, $fred)  Reading into a list: While(<>){ $lines[$index]=$_; $index=$index+1; } print $#lines+1; #This will print out the number of lines print @lines; #This will print out the list itself

15. Resources and Citation.  www.perl.org www.perl.org  http://www.cs.drexel.edu/~knowak/cs265 _fall_2010/Perl_resources.htm http://www.cs.drexel.edu/~knowak/cs265 _fall_2010/Perl_resources.htm

16. The end. Any questions?