As you work in Perl you store each step in source control. When you finish a little bit of work, you commit your work. Ideally, every commit deals with one thing so you’re only introducing one logical change in each revision. Somewhere along the process, you might discover that something is not working correctly. You think that it used to work but you’re not sure where things went pear-shaped, perhaps because the bug seemingly deals with something that you weren’t working on. Continue reading “Locate bugs with source control bisection”
Category: book
Keep your programmatic configuration DRY
A common mantra among programmers today is to keep your code DRY. This little acronym stands for “Don’t Repeat Yourself” and serves as a reminder that when you see a repetitive pattern in your code or are tempted to copy/paste some statements, you should think twice and consider extracting the common logic into a chunk of code that can be reused.
For many programmers, this practice begins to break down when “configuration” code is involved. When I talk about configuration code here, I’m not talking about the XML, YAML, INI, etc. bits of your project. I’m talking about the Perl code in your program that simply serves as data to feed some active portion of your code.
A common mantra among programmers today is to keep your code DRY. This little acronym stands for “Don’t Repeat Yourself” and serves as a reminder that when you see a repetitive pattern in your code or are tempted to copy/paste some statements, you should think twice and consider extracting the common logic into a chunk of code that can be reused. Continue reading “Keep your programmatic configuration DRY”
Set custom DBI error handlers
The DBI module lets you handle errors yourself if you don’t like its built-in behavior. DBI lets you handle the errors at either the database or the statement handle level by specifying attributes: Continue reading “Set custom DBI error handlers”
Respect the global state of the flip flop operator
Perl’s flip-flop operator, .., (otherwise known as the range operator in scalar context) is a simple way to choose a window on some data. It returns false until its lefthand side is true. Once the lefthand side is true, the flip-flop operator returns true until its righthand side is true. Once the righthand side is true, the flip flop operator returns false. That is, the lefthand side turns it on and the righthand side turns it off. Continue reading “Respect the global state of the flip flop operator”
Detect regular expression match variables in your code
[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”
Know when and when not to write networking 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.”
Use Carp::REPL as an interactive Perl shell.
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.”
Use scalar references to pass large data without copying.
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.”
Use B::Deparse to see what perl thinks the code is.
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.”
Compare dates as strings when you can.
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.”