Programming with Perl CSCE 330 Group presentation by: Robert Shannon Robert Shannon Ryan Mullaney Ryan Mullaney Anthony So Anthony So

What is Perl?  Started in 1987 by Larry Wall  Practical Extraction and Reporting Language  Originally developed as a utility for UNIX to replace awk  Currently used as replacement for awk, sed, grep, shell scripts, C…  May be referenced as scripting or programming language depending on the source

Features  Why should I learn Perl?   Similar syntax to C therefore familiar to most programmers   Extremely expressive so a few lines of code will do a lot  Typical uses:  (Common Gate-way Interface) – the interaction between the browser & server  World Wide Web through CGI libraries (Common Gate-way Interface) – the interaction between the browser & server   ActiveX scripting   Processing log files   Windows network administration

Timeline  Oct - Perl 1.0 is released  Jun - Perl 2.0 is released  Oct - Perl 3.0 is released  Mar - Perl 4.0 is released  Jan - MacPerl is released  Dec - MacPerl is released  Feb - Perl is released  Oct - MacPerl is released

Timeline continued  Oct - Perl is released  Mar - Perl is released  Aug - MacPerl is released  Jul - Perl 6 announced  Mar - Perl 5.6 is released  Presently - Perl 6 is still in work

Advantages  Perl is compiled every time it is executed  This allows for easy modifications and portability  Unlike interpretive languages Perl must completely compile before any of it runs  This saves many headaches from partially changed text files  A few lines of Perl can do what it would take a complicated C language program to do.  Many built in functions that save time

Disadvantages  Perl is compiled each time it is executed  Since any one can look at your script and change it there is the issue of security  Limited support for data hiding when dealing with classes.  There are no warnings when variables are coerced between types. Example:  Because of this finding logic errors can be hard  Perl offers a number of ways to do the same thing, some more efficient than others, therefore a badly written Perl script can monopolize system resources.

Syntactical conventions CHARTYPEEXAMPLEEXPLANATION #Comment # Yada Rest of the line is a comment $Scalar$price Variable with single value Array of values (indexed by integers) %Hash%grades Group of values (indexed by strings) <>Handle<STDIN> In- & output for files &Subroutine&doit Executable (Perl-) function

Single or Double Quotes  Single quotes are literal. They will pass on exactly what is inside of them. $myname="David"; print 'Hello World! My name is $myname'; RESULTS : Hello World! My name is $myname  Double quotes variables are interpolated and analyzed for values $myname="David"; print "Hello World! My name is $myname"; RESULTS: Hello World! My name is David

Scalars  A scalar is an individual piece of data. In Java it would be the same as a variable.  Scalar data is symbolized by a $ sign.  For correct processing, the $ must be followed by a letter (non-numeric) character.  Scalar names are CaSe SeNsItIvE. $A is different than $a.  Can use up to 255 characters for a scalar name which includes numbers, letters, and underscores.

Scalars continued $answer = 42; # Interger $pi = ; # Floating point $pet = “Camel”;# string $msg = “I love $pet”; # interpolated string $cost = ‘I costs $100’; # not interpolated $idea = ‘Don\’t do it’; # not interpolated $dst = $src; # Copy variables $x = $y + 5; # expression

Scalar Example $a=5; # a contains value of 5 $b=2.5; # b contains value of 2.5 $a=$b + $a; # a now contains value of 7.5 OR OR $mymessage="Hello World!"; print $mymessage; $mymessage="Bye World!"; print $mymessage; # symbol signifies a comment in the code

Arrays  Arrays are groups of data stored in a single spot.  While scalar data use the $ sign, arrays use symbol.  Example: print "Content-type: text/html\n\n"; print "These are the days of the week: "; print  Results: These are the days of the week: Monday Tuesday Wednesday Thursday Friday Saturday Sunday

Array continued  What about accessing an individual array item? print "The value for the fourth array item is $days[3]"; Notice the use of $ and in this instance. Therefore the breakdown = ("Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday", "Sunday"); Is: $days[0] = "Monday"; $days[1] = "Tuesday"; $days[2] = "Wednesday"; $days[3] = "Thursday"; $days[4] = "Friday"; $days[5] = "Saturday"; $days[6] = "Sunday";

Hashes  Hashes are very similar to an arrays.  A hash is an array of pairs often called an "associative array".  A hash uses the % symbol instead of symbol.  Arrays use 0 to whatever number as an index.  Hashes are keys and value pairs. key, element, key, element, and so on...  Hashes use the curly brackets {} instead of the square brackets [] to find individual elements.

Hash Example %chores = ("Monday", "dishes", "Tuesday", "vacuum", "Wednesday", "garbage"); $value = $chores{Wednesday}; print "$value"; The output of the example script is garbage

Comparison to C C: Void main() { printf(“Hello World!”); }Perl: print ‘Hello World!’

Example of Perl in Action #!c:\perl\bin\perl.exe -w my ($dir); $dir = "."; opendir(DIR, "$dir") || Error("open", "directory"); = readdir(DIR); closedir(DIR) || Error("close", "directory");

sub ren { my ($old_name, $regex = "\.old\$"; $repstr = ".new"; foreach $old_name = $_; $_ =~ s/$regex/$repstr/i; rename($old_name, $_); }} sub Error { print "The server can't $_[0] the $_[1]: $! \n"; }

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