Category: perl

keys in scalar context now returns the number of keys

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.

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You must escape the left brace in a regex

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.

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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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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. Continue reading “Perl v5.24 adds a line break word boundary”

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. Continue reading “Perl v5.22 adds fancy Unicode word boundaries”