℞ 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…
℞ 19: Open file with specific encoding While setting the default Unicode encoding for IO is sensible, sometimes the default encoding is not correct. In this case, specify the encoding for a filehandle manually in the mode option to open…
℞ 18: Make all I/O and args default to utf8 The core rule of Unicode handling in Perl is “always encode and decode at the edges of your program”. If you’ve configured everything such that all incoming and outgoing data…
℞ 17: Make file I/O default to utf8 If you’ve ever had the misfortune of seeing the Unicode warning “wide character in print”, you may have realized that something forgot to set the appropriate Unicode-capable encoding on a filehandle somewhere…
℞ 16: Declare STD{IN,OUT,ERR} to be in locale encoding Always convert to and from your desired encoding at the edges of your programs. This includes the standard filehandles STDIN, STDOUT, and STDERR. While it may be most common for modern…
℞ 15: Declare STD{IN,OUT,ERR} to be UTF-8 Always convert to and from your desired encoding at the edges of your programs. This includes the standard filehandles STDIN, STDOUT, and STDERR. As documented in perldoc perlrun, the PERL_UNICODE environment variable or…
℞ 14: Decode program arguments as locale encoding While it may be most common in modern operating systems for your command-line arguments to be encoded as UTF-8, @ARGV may use other encodings. If you have configured your system with a…
℞ 13: Decode program arguments as utf8 While the standard Perl Unicode preamble makes Perl’s filehandles use UTF-8 encoding by default, filehandles aren’t the only sources and sinks of data. The command-line arguments to your programs, available through @ARGV, may…
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