Effective Perl Programming – write better, more idiomatic Perl
[Lexical $_ was removed in v5.24]
Perl v5.10 introduced given and the lexical $_. That use of $_, which everyone has assumed is a global variable, turned out to be a huge mistake. The various bookkeeping on the global version didn’t happen with the lexical version, so strange things happened. Continue reading “Perl v5.16 now sets proper magic on lexical $_”
Not sure which loop you want to break out of? Perl v5.18 makes that easy with computed labels. The value you give next, last, and redo no longer has to be a literal. You could already do this with goto, but now you can give the loop controllers an expression. Continue reading “Use a computed label with loop controllers”
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”
[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”
Perl v5.20 continues to clean up and optimize its internals. Now perl optimizes a series of lexical variable declarations into a single list declaration. Continue reading “Perl v5.20 combines multiple my() statements”
Perl was once known for its one-liners in its sysadmin heydays. People would pass around lists of these one liners, many of which replaced complicated pipelines that glued together various unix utilities to do some impressive system maintenance. Continue reading “In v5.20, -F implies -a implies -n”
Perl v5.20 adds the “Key/Value Slice”, which extracts multiple keys and their corresponding values from a container (hash or array). It uses the %, which is new, legal syntax for a variable name with subscripts after it: Continue reading “Perl 5.20 introduces “Key/Value Slices””
Want to save 10 nanoseconds? Perl v5.20 optimizes a return at the end of a subroutine to use two fewer ops in the optimized version. During compilation, a subroutine like this one: Continue reading “Perl 5.20 optimizes return at the end of a subroutine”
Prior to v5.20, perl used whatever random number generator the system provided. This meant that the same program could have statistically different results based on the quality of that function. The rand() for Windows had a max of 32,768 (15 bits), while POSIX has drand48 (48 bits). This sort of numerical un-portability has always been a problem with perl since it’s relied on the underlying libc for so much. Continue reading “Perl 5.20 uses its own random number generator”
Perl 5.20 is out and there are some nice syntax changes that make life easier for Perlers, along with some improvements that don’t require any work from you. Some of the features are experimental, so be careful that you don’t create problems by overusing them until they settle down.
You can download the Perl source from CPAN. For Windows, Strawberry Perl 5.20 is available now. The full details are in the perldelta Continue reading “Perl 5.20 new features”