PERL - First Script

With PERL installed we are ready to dive into our first script. There are a few elements every PERL script must contain in order to function. Open up your favorite simple text editor, the file extension for PERL scripts is .pl. Save your files with this extension.
The first line of every PERL script is a commented line directed toward the PERL interpreter. This line is generally the same from one instal of PERL to the next, it might look something like this:
firstscript.pl:
#!/usr/bin/perl
The comment points to the installation path of PERL, usually /usr/bin/perl. If not, you can locate the directory tree to PERL somewhere in the documentation of your web server, or email your web host and they can specify your PERL installation directory.
PERL - HTTP Headers
Because we are working in a web environment we are sort of jumping ahead of the game. We have to introduce some HTTP headers so that PERL understands we are working with a web browser. To do this we have to run another line of strange code called an HTTP header as you may have guessed. It looks something like this:
firstscript.pl:
#!/usr/bin/perl

print "content-type: text/html \n\n";
At this point our script still has no real functionality, all we have done thus far is locate our PERL interpreter and tell it that we are going to be working with a web browser or in a web environment.
PERL - Hello, PERL! Script
Now that we have located the interpreter and told PERL we are working with the web, we can print text to the browser with the print function.
helloperl.pl:
#!/usr/bin/perl

print "content-type: text/html \n\n";

print "Hello, PERL!";
You should see "Hello, PERL!" in the top left corner of your browser, pretty simple and straightforward.
PERL - Execute Your First Script
Now it is time to upload your firstscript.pl to your web server and execute it. After you upload your file be sure to CHMOD the script file and allow anonymous execution priviledge, generally a setting of 0755 works perfectly.
You script is working perfectly if you are staring at a blank screen and didn't recieve a 500 or 404 error message.
PERL - Debugging Your Script(s)
If you are using an FTP program to upload your scripts, set the upload type to ASCII or "Text". This setting prevents the mysterious addition of random characters that sometimes happens when copying files across different operating systems. Learning to do this prevents hours of headaches and frustration.
Another great debugging technique is to isolate the code you are currently working on. To do this you can temporarily comment out lines of code to isolate only the section that is returning an error message.
PERL - Syntax
PERL follows a very specific syntax not unlike other programming languages. It is important to develop good syntax habits as it will save you from having to debug things later, not to mention save yourself from eye strain and mind numbing headaches.
PERL - Case Sensitivity
File names, variables, and arrays are all case sensitive. If you capitalize a variable name when you define it, you must capitalize it to call it.
A great tip for large scripts containing a vast number of variable names it is best to be consistent with your case sensitivity and maybe even develop a system for naming variables that makes sense to you. For the majority of us programmers, capitals are simply not an option.
casesensitivity.pl:
$VAriaBLE_NAmES = "string";
$LIKe_tHESE = "Another String";
$ARe_HArd_to_Type = "A Third String";
PERL - Comments
As with any programming language, PERL offers an escape from your code via the '#' sign. Any words, spaces, or marks after a pound symbol will be ignored by the program interpreter, offering you the coder, a chance to place reminders to yourself about your code. It's a great way to note specifics of your code to yourself or others viewing your code/script. Comments are necessary for any script you wish to publish to others or make readily available.
PERL Comment:
#!/usr/bin/perl

print "Content-type: text/html \n\n"; # the header
#########################################
#Comments start with a #
#########################################
This comment is extreme and overdone, you might see more comments like this in scripts that are offered free on the internet. Often programmers will include a large commented section as an installation or set-up guide included right there in the script itself.
PERL - Escaping Characters
In PERL we use the backslash (\) character to escape any type of character that might interfere with our code. For example there may become a time when you would like to print a dollar sign rather than use one to define a variable. To do this you must "escape" the character using a backslash (\).
escapecharacters.pl:
#!/usr/bin/perl

print "Content-type: text/html \n\n"; #HTTP HEADER

#CREATE STRINGS WITH ESCAPING CHARACTERS
$string = "David paid \$4.34 for Larry\'s shirt.";
$email = "youremail\@youremail.com";

#PRINT THE STRINGS
print "$string
";
print "$email
";
print '$string and $email';
escapecharacters.pl:
David paid $4.34 for Larry's shirt.
youremail@youremail.com
$string and $email
PERL - Define Some Variables
A variable is defined by the ($) symbol (scalar), the (@) symbol (arrays), or the (%) symbol (hashes).
Here is what each type of variable should look like inside of a script.
definevariables.pl:
#!/usr/bin/perl

print "Content-type: text/html \n\n"; #HTTP HEADER

$myname = "some_value";
@array = ("value00","value01","value02");
%hash = ("Quarter", 25, "Dime", 10, "Nickle", 5);
-- OR --
my $myname = "some string";
my @array = ("value00", "value01", "value02");
my %hash =
The latter example using the my parameter is another means to define a variable that you might run across as you gain more experience. It is not necessary to use the my parameter. Variables can be defined either way.