When you store a large string in a scalar, perl allocates the memory to store that string and associate it with the scalar. It uses the same memory even if you assign a much shorter value to the same scalar. Use the functional form of undef to let perl reuse that memory for something else. This is important when you want to reuse the variable or the lifetime of the variable is very long.
Category: item
Perl v5.20 fixes taint problems with locale
Perl v5.20 fixes taint checking in regular expressions that might use the locale in its pattern, even if that part of the pattern isn’t a successful part of the match. The perlsec documentation has noted that taint-checking did that, but until v5.20, it didn’t.
The only approved way to untaint a variable is through a successful pattern match with captures: Continue reading “Perl v5.20 fixes taint problems with locale”
Use postfix dereferencing
[Update: This feature became stable in Perl v5.24]
Perl v5.20 offers an experimental form of dereferencing. Instead of the complicated way I’ll explain in the moment, the new postfix turns a reference into it’s contents. Since this is a new feature, you need to pull it in with the feature pragma (although this feature in undocumented in the pragma docs) (Item 2. Enable new Perl features when you need them. and turn off the experimental warnings: Continue reading “Use postfix dereferencing”
Declare your Pod encoding
Pod::Simple 3.21 changed its behavior when it encountered a non-ASCII character in Pod without an encoding. Instead of handling it quietly, it now gives a warning. That’s not so bad, but Test::Pod uses Pod::Simple, and whenever it sees a warning, pod_ok fails, as it did in my Mac::Errors module: Continue reading “Declare your Pod encoding”
Define grammars in regular expressions
[ This is the 100th Item we’ve shared with you in the two years this blog has been around. We deserve a holiday and we’re taking it, so read us next year! Happy Holidays.]
Perl 5.10 added rudimentary grammar support in its regular expressions. You could define many subpatterns directly in your pattern, use them to define larger subpatterns, and, finally, when you have everything in place, let Perl do the work. Continue reading “Define grammars in regular expressions”
Create your own dualvars
Perl’s basic data type is the scalar, which takes its name from the mathematical term for “single item”. However, the scalar is really two things. You probably know that a scalar can be either a number or a string, or a number that looks the same as its string, or a string that can be a number. What you probably don’t know is that a scalar can be two separate and unrelated values at the same time, making it a dualvar. Continue reading “Create your own dualvars”
Make disposable web servers for testing
If you project depends on a interaction with a web server, especially a remote one, you have some challenges with testing that portion. Even if you can get it working for you, when you distribute your code, someone else might not be able to reach your server for testing. Instead of relying on an external server, you can use a local server that you write especially for your test suite. Continue reading “Make disposable web servers for testing”
Know split’s special cases
Perl’s split has some special cases and some perhaps surprising cases. The empty pattern, zero width match, the special argument ' ', and the /^/ act differently than you might expect from the general rule. Continue reading “Know split’s special cases”
Trace your Perl programs
You can write your own mini (or micro) debuggers to watch your program run. You might want to do this when the other Perl debuggers are too heavyweight (or even too interactive) for your immediate problem. Continue reading “Trace your Perl programs”
Use Data::Printer to debug data structures
You can use several different Perl modules to inspect data structures. Many of these modules, however, are really two tools in one. Besides showing a data structure as a string, they also serialize the data as Perl code so you can reconstruct the data structure. That second job often makes things hard for you. If you don’t need the serialization job, don’t use a module that insists on it. Continue reading “Use Data::Printer to debug data structures”