℞ 39: Case- and accent-insensitive comparisons As you’ve noticed by now, many Unicode strings have multiple possible representations. Comparing two Unicode strings for equality requires far more than merely comparing their codepoints. Not only must you account for multiple representations,…
℞ 38: Making cmp work on text instead of codepoints Even with Perl 5.12’s “unicode_strings” feature, some of Perl’s core operations do not perform as expected on Unicode strings by default. For example, how is the cmp operator to know…
℞ 37: Unicode locale collation As you’ve already seen, Unicode-aware sorting respects Unicode character properties. You can’t sort by codepoint and expect to get accurate results, not even if you stick with pure ASCII. The world is a complicated place….
℞ 36: Case- and accent-insensitive Unicode sort The Unicode Collation Algorithm defines several levels of collation strength by which you can specify certain character properties as relevant or irrelevant to the collation ordering. In simple terms, you can use collation…
℞ 35: Unicode collation Sorting—even pure ASCII—seems easy, at least if you know the alphabet song. Yet even something this simple gets complicated if you sort merely by codepoint. You get numbers coming in the midst of letters. You get…
℞ 34: Unicode column-width for printing Perl’s printf, sprintf, and format think all codepoints take up 1 print column, but many codepoints take 0 or 2. If you use any of these builtins to align text, you may find that…
℞ 33: String length in graphemes If you learn nothing else about Unicode, remember this: characters are not bytes are not graphemes are not codepoints. A user-visible symbol (a grapheme) may be composed of multiple codepoints. Multiple combinations of codepoints…
℞ 32: Reverse string by grapheme Because bytes and characters are not isomorphic in Unicode—and what you may see as a user-visible character (a grapheme) is not necessarily a single codepoint in a Unicode string—every string operation must be aware…
℞ 31: Extract by grapheme instead of by codepoint (substr) The Unicode Standard Annex #29 discusses the boundaries between grapheme clusters—what users might perceive as “characters”. The CPAN module Unicode::GCString allows you to treat a Unicode string as a sequence…
℞ 30: Extract by grapheme instead of by codepoint (regex) Remember that Unicode defines a grapheme as “what a user thinks of as a character”. A codepoint is an integer value in the Unicode codespace. While ASCII conflates the two,…
℞ 29: Match Unicode grapheme cluster in regex In the days of ASCII, we spoke of characters and bytes. We saw few differences between them. In the Unicode world, characters are far more than seven bits of data. Far better…
℞ 28: Convert non-ASCII Unicode numerics Unicode digits encompass far more than the ASCII characters 0 - 9. Unless you’ve used /a or /aa, \d matches more than ASCII digits only. That’s good! Unfortunately, Perl’s implicit string-to-number conversion does not…
℞ 27: Unicode normalization Prescription one reminded you to always decompose and recompose Unicode data at the boundaries of your application. Unicode::Normalize can do much more for you. It supports multiple Unicode Normalization Forms. Normalization, of course, takes Unicode data…
℞ 26: Custom character properties Match Unicode Properties in Regex explained that ever Unicode character has one or more properties, specified by the Unicode consortium. You may extend these rule to define your own properties such that Perl can use…
℞ 25: Match Unicode properties in regex with \p, \P Every Unicode codepoint has one or more properties, indicating the rules which apply to that codepoint. Perl’s regex engine is aware of these properties; use the \p{} metacharacter sequence to…
℞ 24: Disabling Unicode-awareness in builtin charclasses Many regex tutorials gloss over the fact that builtin character classes include far more than ASCII characters. In particular, classes such as “word character” (\w), “word boundary” (\b), “whitespace” (\s), and “digit” (\d)…
℞ 23: Get character category Unicode is a set of characters and a list of rules and properties applied to those characters. The Unicode Character Database collects those properties. The core module Unicode::UCD provides access to these properties. These general…
℞ 22: Match Unicode linebreak sequence in regex Unicode defines several characters as providing vertical whitespace, like the carriage return or newline characters. Unicode also gathers several characters under the banner of a linebreak sequence. A Unicode linebreak matches the…
℞ 21: Unicode case-insensitive comparisons Unicode is more than an expanded character set. Unicode is a set of rules about how characters behave and a set of properties about each character. Comparing strings for equivalence often requires normalizing them to…
℞ 20: Unicode casing Unicode casing is very different from ASCII casing. Some of the complexity of Unicode comes about because Unicode characters may change dramatically when changing from upper to lower case and back. For example, the Greek language…
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