Effective Perl Programming – write better, more idiomatic Perl
Continuing its quest to clean up long deprecated features, v5.28 takes care of another feature deprecated since v5.0. You can no longer neglect to specify a heredoc separator. This was a warning in v5.26 and is now fatal. You probably weren’t doing this anyway (I’ve never seen it in the wild), but it’s nice to know the edge cases are disappearing.
Continue reading “Unquoted empty heredoc terminators are now fatal”
In-place editing is getting much safer in v5.28. Before that, in rare circumstances it could lose data. You may have never noticed the problem and even with all the times I’ve explained it in a Perl class I haven’t really thought about it. This was first reported as early as December 2002 and after we get v5.28 it won’t be a problem anymore. Continue reading “In-place editing gets safer in v5.28”
[Although I haven’t seen an official notice besides a git commit that reverts the changes, by popular outcry these changes won’t be in v5.28. It’s not that they won’t happen but they won’t be in v5.28. People who depend on Perl should stay vigilant. My advice in the first paragraph stands—change is coming and we don’t know what it is yet.]
Perl v5.28 might do away with when—v5.27.7 already has. Don’t upgrade to v5.28 until you know you won’t be affected by this! This change doesn’t follow the normal Perl deprecation or experimental feature policy. If you are using given-when, stop doing that. If you aren’t using it, don’t start. And everyone should consider if a major change like this on such short notice is comfortable for them. It’s not a democracy but you can still let the core developers know which way you want your favorite language to go.
Continue reading “Beware of the removal of when in Perl v5.28”
Stop making huge security holes with POSIX tmpnam. You don’t need it in Perl because File::Temp, which comes with Perl, does it for you. Perl v5.22 deprecated tmpnam (and recommended replacements for tmpfile) and v5.26 has removed it.
Continue reading “Don’t use POSIX to create temporary files”
Starting in v5.26, a hash in scalar context evaluates to the number of keys in the hash. You might have thought that it always did that just like an array (not a list!) in scalar context evaluates to the number of items. But nope—it evaluated to a seemingly useless number called the “hash statistics”. Now it’s fixed to do what most people thought it already did. For what it’s worth, keys (or values) in scalar context already provided the count.
Continue reading “keys in scalar context now returns the number of keys”
Perl v5.28 will have better deprecation warnings. Most of this I picked up from the lightning talk that Abigail gave at The Perl Conference. Continue reading “Deprecation warnings now tell you when the features will disappear”
Update: v5.30 brings this back. The exceptions to allow people to catch up should have already been fixed.
In v5.26 and later, you have to escape the left brace, {, in Perl regular expressions. You probably never thought about this overworked character, but lots of other people have. This is an important change because it’s a fatal issue that may cause your modules and other tools (such as an old version of autoconf!) to stop working. But, we’ve also known about this for a bit, so if you are up-to-date, things may have already been fixed.
{
Continue reading “You must escape the left brace in a regex”
The /xx match operator flag lets you add insignificant horizontal whitespace to character classes. You’ll have to upgrade to v5.26 to use it though, but that release is right around the corner.
The /x has been around since v5.10. That allows you to spread out the parts of your pattern and to add internal comments. This flag makes horizontal whitespace insignificant.
Continue reading “/xx means more meaningless whitespace (and that’s good)”
As of v5.26, the . in @INC is gone by default. When you compile perl, it bakes the default module search path (based on your configure settings) into the binary. These are the paths that perl searches without you adding to @INC with command-line switches or environment variables, and the paths you see when you run perl -V:
Perl v5.24 adds a linebreak word boundary, \b{lb}, to go along the new word boundaries added in v5.22. This is part of Perl’s increasing conformance with the regular expression requirements in Unicode Technical Standard #18. The Unicode::LineBreak implements the same thing, although you have to do a lot more work. Continue reading “Perl v5.24 adds a line break word boundary”