In-place editing gets safer in v5.28

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. » Read more…

Beware of the removal of when in Perl 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.

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Perl v5.28 new features

Perl v5.28 has a few new features and several removals of old features that you shouldn’t have been using anyway (so I’m not going to mention them). » Read more…

Deprecation warnings now tell you when the features will disappear

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. » Read more…

You must escape the left brace in a regex

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.

{

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/xx means more meaningless whitespace (and that’s good)

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.

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v5.26 removes dot from @INC

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:

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Strip leading spaces from here-docs with v5.26

Perl v5.26 allows you to indent heredocs, that special multi-line string quoting mechanism. In v5.24 and earlier, the content of any here-doc included the entire line with any leading whitespace might be there. That meant you typed here-docs in a way the broke the indention of the block that contained them. Perl 6 envisioned a way that this could work and now Perl 5 has stolen some of that.

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Perl v5.24 adds a line break word boundary

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. » Read more…

Perl v5.22 adds fancy Unicode word boundaries

Perl v5.22’s regexes added four Unicode boundaries to go along with the vanilla “word” boundary, \b, that you’ve been using for years. These new assertions aren’t going to match perfectly with your expectations of human languages (the holy grail of natural language processing), but they do okay-ish. Although these appear in v5.22.0, as a late edition to the language they were partially broken in the initial release. They were fixed for v5.22.1. » Read more…