Perl Primer for Mac OSX Users
This Perl Primer is aimed at Mac OSX users who want to learn how to start programming in Perl. It aims to give you enough information to get started writing and running Perl programs on OSX, but won't teach you anything much about the Perl language. There are plenty of good introductions to the Perl language already out there, like this one. For this primer, we'll assume that you don't know anything much about Perl, programming, or the command line, but that you do at least know your way around OSX (e.g. you know what the applications folder is and how to find it). So if you're a web designer or PHP programmer who wants to get started programming in Perl (Hi Steve!) then this is for you.
Perl programs are usually (but not always) run from the command line. In Mac-speak, the command line is usually known as the Terminal application. In the world of Unix (on which OSX is built), people often call it a command line shell, but it's the same thing (or close enough to make no difference). You can find the Terminal in the Applications/Utilities folder. You might want to drag it to the dock so you've got easy access to it in future.
Run the Terminal app and you should see a new window appear with a command line prompt waiting for you to type something. The prompt that you see will usually depend on your machine name and user name. On my machine (called "shiny"), the default prompt for me (user "abw") looks like this:
To avoid any confusion, we'll follow the common convention of showing the
prompt as just
$, like this:
which perl and hit ENTER (from now
on we'll take it as read that you need to hit ENTER at the end of
each line). Remember, you don't need to type the
$ at the start of the line. The examples below
show what you need to type in
green. The output that you
should see is shown in
$ which perl /usr/bin/perl
The command you've just typed is asking your Mac for the location of
perl on your system. It should respond by printing the
/usr/bin/perl. Now type
perl -v. This runs
perl with the
-v) option. Perl will response by printing
its version number and a copyright message.
$ perl -v This is perl, v5.8.8 built for darwin-thread-multi-2level (with 1 registered patch, see perl -V for more detail) Copyright 1987-2006, Larry Wall Perl may be copied only under the terms of either the Artistic License or the GNU General Public License, which may be found in the Perl 5 source kit. Complete documentation for Perl, including FAQ lists, should be found on this system using "man perl" or "perldoc perl". If you have access to the Internet, point your browser at http://www.perl.org/, the Perl Home Page.
The job of the
perl program is to run the Perl programs that
you write. We call this kind of "program that runs other programs" an
interpreter. It reads your Perl program and interprets it into
a language that your computer can understand.
Perl programs are written in plain text files. Mac OSX comes with a very simple TextEdit application (in your Applications folder) which you can use to create plain text files. However, it's not really cut out for any kind of serious programming and you'll do much better using an editor that's been designed specially for that task. I can highly recommend TextMate. Although it's not free, it's very reasonably priced and you can use it free for a month to evaluate it (and no, I'm not on commission :-) There are plenty of other text editors available for the Mac (both free and commercial). Wikipedia has a list to get you started.
Having got yourself a text editor (TextEdit will do just fine for now),
type in the following Perl program and save it to a file called
hello.pl (by the way, if you're using a UK keyboard, the
# character is
You might want to create a new folder for your perl
programs to keep them separate from everything else. We'll assume in these
examples that you create a folder called
perl under your
#!/usr/bin/perl use strict; use warnings; print "Hello World\n";
The first line of the program is a magical incantation that tells Mac OSX
how to run this program. We're telling it to use
the perl interpreter (located at
to make sense of it. The next two lines should appear in every Perl
program you write. The first puts Perl in strict mode, the second
turns on all warnings. Trust me, you want these. Even the Perl
gurus use them religiously, so it's nothing to be ashamed of. The final
line of the program (or the only real line of the program if you
discount the first few lines of pre-amble) prints the message
Hello World to the screen. The
\n at the end of the message is a special code
(usually called an escape sequence) that Perl interprets as a
newline character (another common one is
\t which inserts a
TAB character). The message is quoted using "double quotes" so that Perl
can tell where the message starts and ends. You can also use 'single
quotes' in Perl, but
\t and other escape sequences don't work inside them,
so double quotes is what we want here. Programmers refer to these quoted
things as strings because they represent a string of characters.
Now that you've written and saved your first Perl program you can run
it from the command line. But first we have to find it. If you saved
your Perl program in a new
perl folder then you'll need
to type this at the Terminal prompt:
$ cd perl
cd command tells the terminal to change directory
perl directory. A 'directory' is the Unix name for
what you know as a 'folder'. Same thing, different name. If you saved it
in a directory several levels down then use
/ to separate
each directory name. e.g.
$ cd perl/scripts/test
If you lose track of where you are, the
pwd command will
print the working directory.
$ pwd /Users/abw/perl
Once you've navigated yourself to the directory where your Perl program
is saved, you can use the
ls command to
list the files in that directory. You should
hello.pl file listed.
$ ls hello.pl
You can now run your Perl program by calling the
interpreter and giving it the name of the program file which in this case
Your Perl program should respond by printing the
message and a newline.
$ perl hello.pl Hello World
One final enhancement is to make your new Perl program executable
change mode) Terminal
$ chmod u+x hello.pl
This tells Mac OSX that the user who "owns" the
file (i.e. you) can execute (i.e. run) it as a program. Now you don't need to put
perl in front of your program name. However, you may need
to be a bit more precise about exactly where the program is by
./ in front of the program name.
$ ./hello.pl Hello World
. prefix is Unix-lingo for "the current directory" and
/ is the regular path separator that we use when
talking about files and directories. So the example above is simply
telling Mac OSX that it's the
hello.pl program in the
current directory that we want to run. The reason for this is
because Mac OSX has its own idea about where executable programs live
(e.g. your applications folder) so it goes looking there first. It
doesn't usually bother looking in the current directory (unless you've
specifically configured it to do so) so it needs that extra clue to
find the right file. Alternately, you can spell out the full path to
the program, but that's obviously a little more tedious:
$ /Users/abw/perl/hello.pl Hello World
The best thing about Perl is CPAN.
CPAN is the Comprehensive Perl Archive Network.
In short, it's where you go to find Perl software. Perl software is
distributed as Perl modules. There's nothing particularly special
about Perl modules. They're written in plain text files which you can
load up into your favourite text editor to see how they work. Perl modules
typically have a
.pm file extension instead of
.pl and they're usually distributed in zipped
bundles that come with a
.tar.gz file extension.
Some Perl modules use extensions written in the C programming language. C works at a lower level than Perl so it typically runs faster and allows module authors to do the kind of things that can't be done in Perl alone. In order to use any modules with C extensions, you'll need to have a C compiler installed on your machine. A compiler is a little like an interpreter, except that it does more work up front (i.e. when you install a module) so that it runs faster when you come to use it. Apple provide a C compiler (GCC) as part of the Xcode developer tools. You can install these from your Mac OSX installation disks, or by downloading from the Apple Developer Connection web site.
You can unpack and install Perl modules manually, but most people these
days use the CPAN module to do it for them. This should already be
installed on your Mac. From the Terminal command line, type
sudo cpan to start it running. The
sudo part of the command indicates that you
want to run the
cpan program as the
administrator or "super user" (sudo stands for super
user do). If you're not an administrator of the machine
you're using then you'll have to go and find the administrator and be
nice to him or her. If you are then type your password (the one you use
to login to your Mac) and hit return.
The first time you run the cpan program it will ask you a bunch
of questions so that it can configure itself. Answer the questions as
best you can (just hit RETURN if you're not sure) and then you
should be greeted with a
$ sudo cpan ...a few questions later... cpan>
Now that CPAN is configured, you can use it to install Perl modules. Let's start by installing the DateTime module. You can probably guess what this module is used for!
cpan> install DateTime ...lots of output... All tests successful. Files=43, Tests=3277, 13 wallclock secs ( 0.51 usr 0.20 sys + 10.70 cusr 0.73 csys = 12.14 CPU) Result: PASS DROLSKY/DateTime-0.4501.tar.gz /usr/bin/make test -- OK Running make install Prepending /Users/abw/.cpan/build/DateTime-0.4501-...blah blah blah... Password:enter your password here ...some more output... Appending installation info to /System/Library/Perl/5.8.8/...blah blah blah... DROLSKY/DateTime-0.4501.tar.gz sudo make install -- OK cpan>
Assuming that all the pre-installation tests pass, the CPAN
module will automatically run the
sudo make install
command to install the module. At this point
will prompt you to enter your password to become the super-user. If you're
not an administrator of the machine you're using then you'll have to go
and find the administrator and be nice to him or her.
If the pre-installation tests don't pass then you have two choices. Either
don't use the module, or install it anyway and hope for the best. It's not
uncommon for modules to fail a few minor tests, particularly if the author
wrote it on a different platform to yours and didn't account for minor
differences in filenames, date formats, locales, or any of the other messy
things that make it difficult to write portable code that works everywhere.
force install a module if you want to
use it regardless of any test failures.
cpan> force install SomeDodgyModule
If you do encounter problems then please report them (or see if someone else has already reported them) at http://rt.cpan.org/.
When you're done with the CPAN module, type
exit or hit
(i.e. hold down the Ctrl key and hit D).
Now that you've installed the DateTime module, you can use it in your Perl programs. Here's an example.
#!/usr/bin/perl use strict; use warnings; use DateTime; my $dt = DateTime->now; print "Today is ", $dt->ymd, "\n"; print "The time is", $dt->hms, "\n";
use DateTime; line, in case you can't
figure it out for yourself, tells Perl to that you want to
DateTime module in
your program. The next line creates a
object which represents the current date and time right
now and stores it in a variable called
$dt. The last two lines call the
hms methods on the
and print the values they return in nice, friendly messages. The methods
return the date in
year-month-date format, and
the time in
respectively. Save this program as before and run it from the command
line. You should see output something like this (although the date and
time will obviously be different):
Today is 2008-12-23 The time is 08:33:27
Some object methods accept parameters (also known as
arguments) that affect the way they work. For example, the
hms methods allow
you to specify a different separator. Parameters are passed to the method
by putting them in parentheses immediately after the method name.
print "Today is ", $dt->ymd("/"), "\n"; print "The time is", $dt->hms("."), "\n";
With the above changes, the output is now:
Today is 2008/12/23 The time is 08.33.27
Way to go, dude! You've just written your first Object-Oriented (or OO) program in Perl!
Perl modules come with their own documentation, although the quality and quantity can vary wildly. The perldoc command can be used to read the documentation for a module.
$ perldoc DateTime NAME DateTime − A date and time object SYNOPSIS use DateTime; $dt = DateTime−>new( year => 1964, month => 10, day => 16, hour => 16, minute => 12, second => 47, nanosecond => 500000000, time_zone => ’Asia/Taipei’, ); $dt = DateTime−>from_epoch( epoch => $epoch ); $dt = DateTime−>now; # same as ( epoch => time() ) ...etc...
You can also use perldoc to read the internal documentation for Perl.
$ perldoc perl NAME perl − Practical Extraction and Report Language SYNOPSIS perl [ −sTtuUWX ] [ −hv ] [ −V[:configvar] ] [ −cw ] [ −d[t][:debugger] ] [ −D[number/list] ] [ −pna ] [ −Fpattern ] [ −l[octal] ] [ −0[octal/hexadecimal] ] [ −Idir ] [ −m[−]module ] [ −M[−]’module...’ ] [ −f ] [ −C [number/list] ] [ −P ] [ −S ] [ −x[dir] ] [ −i[extension] ] [ −e ’command’ ] [ −− ] [ programfile ] [ argument ]... If you’re new to Perl, you should start with perlintro, which is a general intro for beginners and provides some background to help you navigate the rest of Perl’s extensive documentation. For ease of access, the Perl manual has been split up into several sections. Overview perl Perl overview (this section) perlintro Perl introduction for beginners perltoc Perl documentation table of contents ...etc...
As the documentation explains, the Perl manual is split up into several sections. You can use perldoc to read any of the sections listed.
$ perldoc perlintro NAME perlintro −− a brief introduction and overview of Perl DESCRIPTION This document is intended to give you a quick overview of the Perl programming language, along with pointers to further documentation. ...etc...
You can also use perldoc to read the documentation for Perl's internal functions. You must use the -f (for function) option followed by the name of the function. For example, if you want to find out more about the split function used to split strings into smaller parts then you can type this from the command line:
$ perldoc -f split split /PATTERN/,EXPR,LIMIT split /PATTERN/,EXPR split /PATTERN/ split Splits the string EXPR into a list of strings and returns that list. By default, empty leading fields are preserved, and empty trailing ones are deleted. (If all fields are empty, they are considered to be trailing.) ...etc...
perldoc has a number of other options to help you browse around the Perl documentation. To see a full list of options, run perldoc -h for help.
$ perldoc -h perldoc [options] PageName|ModuleName|ProgramName... perldoc [options] -f BuiltinFunction perldoc [options] -q FAQRegex Options: -h Display this help message -V report version -r Recursive search (slow) -i Ignore case -t Display pod using pod2text instead of pod2man and nroff (-t is the default on win32 unless -n is specified) -u Display unformatted pod text -m Display module's file in its entirety -n Specify replacement for nroff ...etc...You can also read the Perl documentation online at http://perldoc.perl.org/.
If you haven't already read this introduction to Perl, then you should probably do that next.
If dead trees are your thing then Learning Perl is a good place to start. After that, Programming Perl is the definitive book on Perl programming. If you only own one Perl book, it should be this one.
Programming Perl is fun, but drinking beer is more fun. If you're enjoying Perl and want to learn more, or meet up with like-minded Perl folk, drink beer and discuss things Perlish, then you should seek out your local Perl Mongers group. If you haven't got a local group then either start one of your own or join London.pm because we've got members from all over the world and don't care where you live as long as you dig Perl. There's a mailing list where you can post questions about Buffy the Vampire Slayer, fine ales, ponies, or even something related to Perl. Perl is a fun programming language, and so are the people. But please enjoy them responsibly. Don't drink and code Perl. Not unless your laptop is beerproof.