Perl 101 (Part 1) - The Basics - Your First Perl Program (
Page 3 of 5 ) And now that you've got Perl installed and
configured, how about actually doing something with it? Use your favourite text
editor to type the following lines of code:
#!/usr/bin/perl
# Perl 101
print ("Groovy, baby!\n");
Save this file as "groovy.pl". Next, you need to tell the system that the
file is executable. On a UNIX system, this is accomplished by setting the
"executable bit" with the "chmod" command:
$ chmod +x groovy.pl
And now run the script - in UNIX, try
$ ./groovy.pl
On a Windows system, you need to pass the name of the script to the Perl
executable as a parameter, like this:
> perl groovy.pl
or
> groovy.pl
In both cases, the script should return Austin Powers' trademark line. Ain't
Perl groovy, baby!
In case things don't work as they should, it usually
means that the system was unable to locate the Perl binary. This is a good time
to holler for the system administrator.{mospagebreak title=Your First Perl
Program Dissected} Let's take a closer look at the script. The first line
#!/usr/bin/perl
is used to indicate the location of the Perl binary. This line must be included
in each and every Perl script, and its omission is a common cause of heartache
for novice programmers. Make it a habit to include it, and you'll live a
healthier, happier life.
Next up, we have a comment.
# Perl 101
Comments in Perl are preceded by a hash [#] mark. If you're planning to make
your code publicly available on the Internet, a comment is a great way to tell
members of the opposite sex all about yourself - try including your phone number
for optimum results.
And finally, the meat of the script:
print ("Groovy, baby!\n");
In Perl, a line of code like the one above is called a "statement". Every Perl
program is a collection of statements, and a statement usually contains
instructions to be carried out by the Perl interpreter.
In this
particular statement, the print() function has been used to send a line of text
to the screen. Like all programming languages, Perl comes with a set of built-in
functions - the print() function is one you'll be seeing a lot of in the future.
The text to be printed is included within double quotes, and the entire thing is
then surrounded by parentheses. Note the n character, used to indicate a new
line.
C programmers will be familiar with the print() function call
above, as also with the fact that in C, it is mandatory to place function
arguments within parentheses. Perl is more flexible than C in this regard - in
many cases, parentheses can be excluded in function calls, as in this example:
#!/usr/bin/perl
# Perl 101
print "Groovy, baby!\n";
Every Perl statement ends with a semi-colon. Don't ask why - just do
it!
And here's an interesting bit of trivia - every Perl statement can be
further sub-divided into smaller units called "tokens". If you take a look at
the statement above, you'll see three distinct tokens - print, ("Groovy,
baby!\n") and the semi-colon. The interesting thing about tokens is that they
can be separated with white space and tabs - which, translated, means that you
could also write the above line as
print ("Groovy, baby!\n") ;
or
print("Groovy, baby!\n") ;
and things would still work as advertised. Needless to say, this comes in very
useful when dealing with long and complex scripts.{mospagebreak title=Two Plus
Two} So now you know how to print text - how about a little math? Try this:
#!/usr/bin/perl
# Some addition
print (10+2);
And this should give you the answer of that particular
mathematical operation.
You can even try subtraction, multiplication and
division:
#!/usr/bin/perl
# Some more math
print (10-2);
print (10 * 2);
print (10/2);
Note how the various results are concatenated together in the
absence of the newline character.
And you can even combine text and
mathematical operations - this will be covered in greater detail over the next
few weeks, but for the moment, you can play with this simple example:
#!/usr/bin/perl
# Synthesis
print ("Hello there! And what are you doing ",
1+1, "night, baby?\n");
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