Effective Perl Programming – write better, more idiomatic Perl
[UPDATE: this is not a problem in v5.18 and later.]
In Item 33: “Watch out for match variables”, you found out that the match variable $`, $&, and $` come with a performance hit. With all of the module code that you might use, you might be using those variables even though you didn’t code with them yourself. Continue reading “Detect regular expression match variables in your code”
Even though Perl has support for low-level socket programming, that doesn’t mean that you have to program at the low-level. For common protocols such as FTP, HTTP, POP3, or SMTP, you can use modules that come with Perl to handle the transport details. libnet, the distribution that comprises the basic protocols, comes with Perl since 5.8. Many other protocols, such as SSH, have implementations on CPAN. You can also install from CPAN many higher level libraries, such as LWP and WWW::Mechanize. Continue reading “Know when and when not to write networking code.”
Wouldn’t it be great if you could stop your program right before it died so you could see what’s causing the problem? You could start the Perl debugger and step your way to the problem, or set up some break points, but that’s often too much work. The Carp::REPL module let’s you drop into a debugger just at the point you need. Continue reading “Use Carp::REPL as an interactive Perl shell.”
References aren’t just for data structures, and many people overlook the benefit of references to simple scalars. With references to arrays and hashes you can keep those data structures in tact when you pass them to or return them from subroutines (Item 46: Pass references instead of copies). You don’t need to worry about scalar values because they are a single item in both the non-reference and reference form. Continue reading “Use scalar references to pass large data without copying.”
Before Perl 5.12, each only took a hash argument. In list context, it returns a two item list of a key-value pair you had not seen yet (unless you changed the hash in some way that re-ordered it): Continue reading “Use each() on an array in Perl 5.12.”
We used B::Deparse in Item 7. Know which values are false and test them accordingly, but we didn’t say much about that module. The B namespace has many modules that do various nasty black magic things with the perl parse tree. Continue reading “Use B::Deparse to see what perl thinks the code is.”
Just because you find a module that does something doesn’t mean that you have to use it. There are many excellent date and time modules on CPAN, including most people’s favorite, DateTime. In your heady rush for program purity and elegance, don’t think that you always have to use objects to do your work. Sometimes the overhead of objects, which have to call (perhaps many) subroutines to do their work, is too expensive. Continue reading “Compare dates as strings when you can.”
In Perl, a subroutine or other block structure that returns a value gives back the last evaluated expression, but if you’re not careful you might not recognize what that last evaluation actually is. It’s not necessarily the last statement in the block; it’s just the last one that you actually execute. For this Item, forget about the best practice of using explicit returns. You should do that for precisely the reasons you will see here, but you can’t learn about the problem by avoiding it. Continue reading “Know what your the last evaluated expression actually is.”
There is a lot going on when you use DBI to interact with a database. Tack on a few layers of abstraction from Object Relational Modelers (ORM’s) such as DBIx::Class and you can end up with a tricky maze of subroutine calls to dig through when you need to track down issues. DBI comes with a built-in tracing feature to make it easier though. Continue reading “Use DBI_TRACE to follow DBI’s work.”
Usually, you want to do as much of your work inside your Perl program as you can. CPAN has a wealth of modules that accomplish many tasks, including those that you normally do very easily from the command line. In the cases where you can’t find a module, you might not be able to improve on the command-line siutation for complicated tasks. Perl is, after all, a glue language, so you don’t always have to do everything in Perl. When you decide to use an external program, there are many Perl features waiting to help, although you have to choose the right one for the job. Continue reading “Interact with the system when Perl isn’t enough”