If you are using a Mac (implied by Xcode) open terminal window and type:

perl -v
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That should get you something that looks a little like:

This is perl 5, version 16, subversion 3 (v5.16.3) built for MSWin32-x
+86-multi-thread
(with 1 registered patch, see perl -V for more detail)

Copyright 1987-2012, Larry Wall

Binary build 1603 [296746] provided by ActiveState http://www.ActiveSt
+ate.com
Built Mar 13 2013 11:29:21

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 ki
+t.

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 Pa
+ge.
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The details will be different because I'm using a Windows machine so my Perl was build for Windows, but that doesn't matter much. If that worked, cd to somewhere you can create files (your home directory ~ would be a reasonable place) and type: nano hello.pl then press return. In the nano editor enter:

#!/usr/bin/perl
use strict;
use warnings;

print "Hello World\n";
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Press Ctrl-X then Y and return to exit and save your changes to the file hello.pl. Type perl hello.pl then return. You have now written and run your first Perl program. For extra points you can chmod ug+x hello.pl to make the script executable without needing to use the Perl interpreter directly. You can then just ./hello.pl.

You should now be in a position to run examples and do exercises from the book.