PERLUNICODE(1)
PERLUNICODE(1) — Perl Programmers Reference Guide 💅
NAME 🦋
perlunicode — Unicode support in Perl
DESCRIPTION ✨
Okay bestie, if you haven't already, pls go get comfy with perlunitut and perluniintro before you read this. Like, actually. It's giving prerequisites. 💖
Unicode? It's literally trying to UNI-fy the en-CODE-ings of every character set in the world into one single Standard. Iconic behavior. Back when Unicode was first created, a bunch of coding standards existed, and for quite a few of them, converting from each to Unicode basically meant adding a constant to every code point in the original standard. Converting back? Just subtract that same constant. So easy. For ASCII and ISO-8859-1, that constant is 0. For ISO-8859-5 (Cyrillic), it's 864; for Hebrew (ISO-8859-8), it's 1488; Thai (ISO-8859-11), 3424; and so forth. This made conversions easy and helped Unicode get adopted. Slay.
And it worked! Nowadays those legacy standards are rarely used. Most everyone uses Unicode. Periodt.
Unicode is a comprehensive standard. It specifies many things outside the scope of Perl, such as how to display sequences of characters. For a full discussion of all aspects of Unicode, see <https://www.unicode.org>.
Important Caveats 🚨
Even if some of this section is confusing on first read, we think it's important enough to highlight the gotchas before going further, so here goes:
Unicode support is an extensive requirement. While Perl does not implement the Unicode standard or the accompanying technical reports from cover to cover, Perl does support many Unicode features.
Also, using Unicode may present security issues that aren't obvious, see "Security Implications of Unicode" below.
Safest if you use feature 'unicode_strings'
In order to preserve backward compatibility, Perl does not turn on full internal Unicode support unless the pragma use feature 'unicode_strings' is specified. (This is automatically selected if you use v5.12 or higher.) Failure to do this can trigger unexpected surprises. See "The "Unicode Bug"" below.
This pragma doesn't affect I/O. Nor does it change the internal representation of strings, only their interpretation. There are still several places where Unicode isn't fully supported, such as in filenames.
Input and Output Layers
Use the :encoding(...) layer to read from and write to filehandles using the specified encoding. (See open.)
You must convert your non-ASCII, non-UTF-8 Perl scripts to be UTF-8.
The encoding module has been deprecated since perl 5.18 and the perl internals it requires have been removed with perl 5.26.
use utf8 still needed to enable UTF-8 in scripts
If your Perl script is itself encoded in UTF-8, the use utf8 pragma must be explicitly included to enable recognition of that (in string or regular expression literals, or in identifier names). This is the only time when an explicit use utf8 is needed. (See utf8.)
If a Perl script begins with the bytes that form the UTF-8 encoding of the Unicode BYTE ORDER MARK (BOM, see "Unicode Encodings"), those bytes are completely ignored.
UTF-16 scripts autodetected
If a Perl script begins with the Unicode BOM (UTF-16LE, UTF16-BE), or if the script looks like non-BOM-marked UTF-16 of either endianness, Perl will correctly read in the script as the appropriate Unicode encoding.
Byte and Character Semantics 💾
Before Unicode, most encodings used 8 bits (a single byte) to encode each character. So a character was a byte, a byte was a character, and there could only be 256 or fewer possible characters. "Byte Semantics" in the title of this section refers to this behavior. There was no need to distinguish between "Byte" and "Character".
Then along comes Unicode, which has room for over a million characters (and Perl allows for even more). This means a character may require more than a single byte to represent it, so the two terms are no longer equivalent. What matters are the characters as whole entities, and not usually the bytes that comprise them. That's what "Character Semantics" in the title of this section refers to.
Perl had to change internally to decouple "bytes" from "characters". It is important that you too change your ideas, if you haven't already, so that "byte" and "character" no longer mean the same thing in your mind.
The basic building block of Perl strings has always been a "character". The changes basically come down to that the implementation no longer thinks that a character is always just a single byte.
There are various things to note:
- String handling functions, for the most part, continue to operate in terms of characters.
length(), for example, returns the number of characters in a string, just as before. But that number no longer is necessarily the same as the number of bytes in the string (there may be more bytes than characters). The other such functions includechop(),chomp(),substr(),pos(),index(),rindex(),sort(),sprintf(), andwrite().
The exceptions are:
- the bit-oriented
vec - the byte-oriented
pack/unpackCformat
However, the W specifier does operate on whole characters, as does the U specifier.
- some operators that interact with the platform's operating system
Operators dealing with filenames are examples.
- when the functions are called from within the scope of the
use bytespragma
Likely, you should use this only for debugging anyway.
- Strings--including hash keys--and regular expression patterns may contain characters that have ordinal values larger than 255.
If you use a Unicode editor to edit your program, Unicode characters may occur directly within the literal strings in UTF-8 encoding, or UTF-16. (The former requires a use utf8, the latter may require a BOM.)
"Creating Unicode" in perluniintro gives other ways to place non-ASCII characters in your strings.
- The
chr()andord()functions work on whole characters. - Regular expressions match whole characters. For example,
.matches a whole character instead of only a single byte. - The
tr///operator translates whole characters. (Note that thetr///CUfunctionality has been removed. For similar functionality to that, seepack('U0', ...)andpack('C0', ...)). scalar reverse()reverses by character rather than by byte.- The bit string operators,
& | ^ ~and (starting in v5.22)&. |. ^. ~.can operate on bit strings encoded in UTF-8, but this can give unexpected results if any of the strings contain code points above0xFF. Starting in v5.28, it is a fatal error to have such an operand. Otherwise, the operation is performed on a non-UTF-8 copy of the operand. If you're not sure about the encoding of a string, downgrade it before using any of these operators; you can useutf8::utf8_downgrade().
The bottom line is that Perl has always practiced "Character Semantics", but with the advent of Unicode, that is now different than "Byte Semantics".
ASCII Rules versus Unicode Rules 🔤
Before Unicode, when a character was a byte was a character, Perl knew only about the 128 characters defined by ASCII, code points 0 through 127 (except for under use locale). That left the code points 128 to 255 as unassigned, and available for whatever use a program might want. The only semantics they have is their ordinal numbers, and that they are members of none of the non-negative character classes. None are considered to match \w for example, but all match \W.
Unicode, of course, assigns each of those code points a particular meaning (along with ones above 255). To preserve backward compatibility, Perl only uses the Unicode meanings when there is some indication that Unicode is what is intended; otherwise the non-ASCII code points remain treated as if they are unassigned.
Here are the ways that Perl knows that a string should be treated as Unicode:
- Within the scope of
use utf8
If the whole program is Unicode (signified by using 8-bit Unicode Transformation Format), then all literal strings within it must be Unicode.
- Within the scope of
use feature 'unicode_strings'
This pragma was created so you can explicitly tell Perl that operations executed within its scope are to use Unicode rules. More operations are affected with newer perls. See "The "Unicode Bug"".
- Within the scope of
use v5.12or higher
This implicitly turns on use feature 'unicode_strings'.
- Within the scope of
use locale 'not_characters', oruse localeand the current locale is a UTF-8 locale.
The former is defined to imply Unicode handling; and the latter indicates a Unicode locale, hence a Unicode interpretation of all strings within it.
- When the string contains a Unicode-only code point
Perl has never accepted code points above 255 without them being Unicode, so their use implies Unicode for the whole string.
- When the string contains a Unicode named code point
\N{...}
The \N{...} construct explicitly refers to a Unicode code point, even if it is one that is also in ASCII. Therefore the string containing it must be Unicode.
- When the string has come from an external source marked as Unicode
The -C command line option can specify that certain inputs to the program are Unicode, and the values of this can be read by your Perl code, see ${^UNICODE} in perlvar.
- When the string has been upgraded to UTF-8
The function utf8::utf8_upgrade() can be explicitly used to permanently (unless a subsequent utf8::utf8_downgrade() is called) cause a string to be treated as Unicode.
- There are additional methods for regular expression patterns
A pattern that is compiled with the /u or /a modifiers is treated as Unicode (though there are some restrictions with /a). Under the /d and /l modifiers, there are several other indications for Unicode; see "Character set modifiers" in perlre.
Note that all of the above are overridden within the scope of use bytes; but you should be using this pragma only for debugging.
Note also that some interactions with the platform's operating system never use Unicode rules.
When Unicode rules are in effect:
- Case translation operators use the Unicode case translation tables.
Ok bestie, quick little note before we keep going: uc(), or "\U" when it's inlined in an interpolated string, translates stuff to uppercase. Meanwhile ucfirst, or "\u" in an interpolated string, translates to titlecase — but only in languages that actually make that distinction. In languages that don't? Titlecase is just uppercase, no biggie, same thing. 💅
There's a CPAN module called "Unicode::Casing" that lets you define your own mappings for lc(), lcfirst(), uc(), ucfirst(), and "fc" (or their double-quoted inlined versions like "\U"). Lowkey important lore: before Perl 5.16, the Perl core partially did this, but it had a bunch of insurmountable drawbacks, so they just wrote the CPAN module instead. Character development. 🌸
- Character classes in regular expressions match based on the character properties in the Unicode properties database. Like,
"\w"can match a Japanese ideograph, for instance, and[[:digit:]]matches a Bengali number. Yes bestie, your regex ate that. ✨ - Named Unicode properties, scripts, and block ranges can be used (like bracketed character classes) with the
"\p{}""matches property" construct, and its negation"\P{}"which is "doesn't match property".- Peep "Unicode Character Properties" for way more on this. 👀
- You can also define your own character properties and use them in regex with
"\p{}"or"\P{}". See "User-Defined Character Properties" for the tea.
🦋 Extended Grapheme Clusters (Logical characters) 🦋
So picture a character, let's say "H". Now imagine it wearing accessories — an acute accent, a circumflex, hooks, circles, arrows, above, below, off to one side or the other, whatever. The world's languages have so many possibilities here. The number of combos is genuinely astronomical, and if Unicode made a single character for every single combo it would blow through its more than a million possible characters instantly. Not sustainable, bestie. 😭
So Unicode took a different approach: there's a character for the base "H", and a character for each possible mark, and you combine them however you need to get the final logical character. So a logical character — the thing that looks like one single character — can actually be a whole sequence of more than one individual character. The Unicode standard calls these "extended grapheme clusters" (which is the glow-up version of the old "grapheme cluster" that nobody really uses anymore). And Perl gives you the "\X" regular expression construct to match those sequences in their entirety. Iconic. 👑
But here's the thing — Unicode's whole goal is to unify all the existing character set standards and practices, and several pre-existing standards already have single characters that mean the same thing as some of these combos. Like ISO-8859-1, which has quite a few of them. For example, "LATIN CAPITAL LETTER E WITH ACUTE" was already chilling in that standard before Unicode even showed up. So Unicode added it to its repertoire as that single character. But Unicode considers this character equivalent to the sequence of the character "LATIN CAPITAL LETTER E" followed by the character "COMBINING ACUTE ACCENT".
"LATIN CAPITAL LETTER E WITH ACUTE" is called a "pre-composed" character, and its equivalence with the "E" + "COMBINING ACCENT" sequence is called canonical equivalence. Every pre-composed character is said to have a decomposition (into the equivalent sequence), and that decomposition type is also called canonical. A string can be as precomposed as possible, or fully decomposed, and Unicode calls those respectively "Normalization Form Composed" (NFC) and "Normalization Form Decomposed". The "Unicode::Normalize" module has functions to convert between the two. A string can also be a mix of composed and decomposed characters — this module can make it all one or the other. ✨
You may get handed strings in any of these equivalent forms. And rn there is currently nothing in Perl 5 that ignores the differences. So you'll have to specially handle it yourself. The usual advice is to convert your inputs to "NFD" before processing any further. Do it, bestie, future you will thank you. 🫶
For more detailed info, see <http://unicode.org/reports/tr15/>.
💜 Unicode Character Properties 💜
(Real talk: the only time Perl treats a sequence of individual code points as a single logical character is in the "\X" construct we just talked about. So for everything below, "character" means a single Unicode code point. Got it? Good. 💅)
Very nearly all Unicode character properties are reachable through regular expressions using the "\p{}" "matches property" construct, and "\P{}" "doesn't match property" for the negation.
For instance, "\p{Uppercase}" matches any single character with the Unicode "Uppercase" property, while "\p{L}" matches any character whose "General_Category" is "L" (letter) — see "General_Category" below. And no, you don't need brackets for single letter property names, so "\p{L}" is equivalent to "\pL". Slay.
More formally: "\p{Uppercase}" matches any single character whose Unicode "Uppercase" property value is "True", and "\P{Uppercase}" matches any character whose "Uppercase" property value is "False". Those could also have been written as "\p{Uppercase=True}" and "\p{Uppercase=False}", respectively. Same energy.
This formality matters when properties are not binary — i.e., when they can take on more values than just "True" and "False". For example, the "Bidi_Class" property (see "Bidirectional Character Types" below) can take on several different values like "Left", "Right", "Whitespace", and others. To match those you need to specify both the property name ("Bidi_Class") AND the value you're matching against ("Left", "Right", etc.). You do that, like in the examples above, by putting the two components separated by an equal sign (or interchangeably, a colon), like "\p{Bidi_Class: Left}". Easy. 💅
Every Unicode-defined character property can be written in these compound forms "\p{property=value}" or "\p{property:value}". But Perl also gives you some extra properties that are written only in the single form, plus single-form short-cuts for all binary properties and certain others described below, where you can just omit the property name and the equals-or-colon separator entirely. Convenient queen. 👑
Most Unicode character properties have at least two synonyms (or aliases, if that's your vibe): a short one that's easier to type, and a longer one that's more descriptive and therefore easier to understand. So the "L" and "Letter" properties above are equivalent and interchangeable. Likewise, "Upper" is a synonym for "Uppercase", so we could have written "\p{Uppercase}" as "\p{Upper}". There are also usually various synonyms for the values a property can take. For binary properties, "True" has 3 synonyms: "T", "Yes", and "Y"; and "False" correspondingly has "F", "No", and "N".
⚠️ But be careful, bestie!! A short form of a value for one property might not mean the same thing as the short form spelled identically for another. So for the"General_Category"property,"L"means"Letter"— but for the"Bidi_Class"property,"L"means"Left". 😭 A complete list of properties and synonyms lives in perluniprops.
Upper/lower case differences in property names and values? Irrelevant. So "\p{Upper}" means the same as "\p{upper}" or even "\p{UpPeR}". Same deal with underscores — you can add or delete them anywhere in the middle of a word, so "\p{U_p_p_e_r}" is equivalent too. And white space is generally irrelevant next to non-word characters like the braces and the equals-or-colon separators, so "\p{ Upper }" and "\p{ Upper_case : Y }" are equivalent to all of these as well. Honestly white space and even hyphens can usually be added or deleted anywhere, so even "\p{ Up-per case = Yes}" is equivalent. Unicode calls all of this "loose-matching". The "name" property has some restrictions on this because of a few outlier names. Full details are in <https://www.unicode.org/reports/tr44/tr44-24.html#UAX44-LM2>. 🎀
The few places where stricter matching is used: in the middle of numbers, in the "name" property, and in the Perl extension properties that begin or end with an underscore. Stricter matching actually cares about white space (except adjacent to non-word characters), hyphens, and non-interior underscores. ✨
You can also use negation in both "\p{}" and "\P{}" by dropping a caret ("^") between the first brace and the property name: "\p{^Tamil}" is equal to "\P{Tamil}". Neat.
Almost all properties are immune to case-insensitive matching — meaning adding a /i regular expression modifier does not change what they match. But there are two sets that are affected:
- The first set is
"Uppercase_Letter","Lowercase_Letter", and"Titlecase_Letter"— all of which match"Cased_Letter"under/imatching. - The second set is
"Uppercase","Lowercase", and"Titlecase"— all of which match"Cased"under/imatching. This set also includes its subsets"PosixUpper"and"PosixLower", both of which under/imatch"PosixAlpha".
(The difference between these sets, btw, is that some things like Roman numerals come in both upper and lower case, so they're "Cased" — but they aren't considered letters, so they aren't "Cased_Letter"s. The more you know. 🌈)
See "Beyond Unicode code points" for special considerations when matching Unicode properties against non-Unicode code points. 👀
🌸 General_Category 🌸
Every Unicode character is assigned a general category, which is the "most usual categorization of a character" (from <https://www.unicode.org/reports/tr44>).
The compound way of writing these is like "\p{General_Category=Number}" (short: "\p{gc:n}"). But Perl hands you shortcuts where everything up through the equal or colon separator is just omitted. So instead you can literally just write "\pN". Periodt. 💅
Here are the short and long forms of the values the "General Category" property can have:
Short Long
L Letter
LC, L& Cased_Letter (that is: [\p{Ll}\p{Lu}\p{Lt}])
Lu Uppercase_Letter
Ll Lowercase_Letter
Lt Titlecase_Letter
Lm Modifier_Letter
Lo Other_Letter
M Mark
Mn Nonspacing_Mark
Mc Spacing_Mark
Me Enclosing_Mark
N Number
Nd Decimal_Number (also Digit)
Nl Letter_Number
No Other_Number
P Punctuation (also Punct)
Pc Connector_Punctuation
Pd Dash_Punctuation
Ps Open_Punctuation
Pe Close_Punctuation
Pi Initial_Punctuation
(may behave like Ps or Pe depending on usage)
Pf Final_Punctuation
(may behave like Ps or Pe depending on usage)
Po Other_PunctuationS— SymbolSm— Math_SymbolSc— Currency_SymbolSk— Modifier_SymbolSo— Other_SymbolZ— SeparatorZs— Space_SeparatorZl— Line_SeparatorZp— Paragraph_SeparatorC— OtherCc— Control (also Cntrl)Cf— FormatCs— SurrogateCo— Private_UseCn— Unassigned
Okay so here's the tea on the single-letter ones bestie: a single-letter property matches every character in any of the two-letter sub-properties that start with that same letter. But LC and L& are the special girlies — both of them are aliases for the set made up of literally everything matched by Ll, Lu, and Lt. Periodt. 💅
🧭 Bidirectional Character Types 🧭
Not all scripts vibe in the same direction, and that's iconic of them. Hebrew and Arabic are written right to left, for example, so Unicode hands us a Bidi_Class property to keep track. Some of the values this property can have are:
L— Left-to-RightLRE— Left-to-Right EmbeddingLRO— Left-to-Right OverrideR— Right-to-LeftAL— Arabic LetterRLE— Right-to-Left EmbeddingRLO— Right-to-Left OverridePDF— Pop Directional FormatEN— European NumberES— European SeparatorET— European TerminatorAN— Arabic NumberCS— Common SeparatorNSM— Non-Spacing MarkBN— Boundary NeutralB— Paragraph SeparatorS— Segment SeparatorWS— WhitespaceON— Other Neutrals
This property is always written in the compound form, no exceptions. So like, \p{Bidi_Class:R} matches characters that are normally written right to left. And unlike the General_Category property, this one can get more values added in a future Unicode release. The ones listed above were the complete set for many Unicode releases, but others got added in Unicode 6.3 — you can always find what the current ones are in perluniprops. And https://www.unicode.org/reports/tr9/ describes how to use them. 🫶
📜 Scripts 📜
The world's languages are written in soooo many different scripts. This sentence (unless you're reading it in translation) is written in Latin, Russian is written in Cyrillic, Greek is written in — well — Greek, and Japanese is mainly Hiragana or Katakana. And there are many more.
The Unicode Script and Script_Extensions properties tell you what script a given character lives in. Script_Extensions is the glow-up version of Script, and we're gonna demonstrate that below. Either property can be specified with the compound form like \p{Script=Hebrew} (short: \p{sc=hebr}), or \p{Script_Extensions=Javanese} (short: \p{scx=java}). On top of that, Perl hands out shortcuts for all the Script_Extensions property names. You can just skip everything up through the equals (or colon) and simply write \p{Latin} or \P{Cyrillic}. (This is not true for Script — that one is required to be written in the compound form. Prior to Perl v5.26, the single form returned the plain old Script version, but that got changed because Script_Extensions gives better results. we love an upgrade ✨)
So what's the actual difference between these two properties? It's all about characters that get used across multiple scripts. For example, the digits '0' through '9' are used in like, many parts of the world. Those get placed in a script named Common. Other characters only get used in a few scripts. For example, the KATAKANA-HIRAGANA DOUBLE HYPHEN is used in both Japanese scripts, Katakana and Hiragana, but nowhere else. The Script property puts all characters used in multiple scripts into the Common script, while the Script_Extensions property puts the ones used in only a few scripts into each of those scripts — while still using Common for the ones used in many scripts.
So both of these match:
"0" =~ /\p{sc=Common}/ # Matches
"0" =~ /\p{scx=Common}/ # Matchesand only the first of these match:
"\N{KATAKANA-HIRAGANA DOUBLE HYPHEN}" =~ /\p{sc=Common} # Matches
"\N{KATAKANA-HIRAGANA DOUBLE HYPHEN}" =~ /\p{scx=Common} # No matchAnd only the last two of these match:
"\N{KATAKANA-HIRAGANA DOUBLE HYPHEN}" =~ /\p{sc=Hiragana} # No match
"\N{KATAKANA-HIRAGANA DOUBLE HYPHEN}" =~ /\p{sc=Katakana} # No match
"\N{KATAKANA-HIRAGANA DOUBLE HYPHEN}" =~ /\p{scx=Hiragana} # Matches
"\N{KATAKANA-HIRAGANA DOUBLE HYPHEN}" =~ /\p{scx=Katakana} # MatchesSo Script_Extensions is basically an improved Script where fewer characters sit in the Common script and correspondingly more sit in other scripts. It's new in Unicode version 6.0, and ngl its data are likely to change significantly in later releases, as things get sorted out. New code should probably be using Script_Extensions and not plain Script. If you compile perl with a Unicode release that doesn't have Script_Extensions, the single form Perl extensions will instead refer to the plain Script property. And if you compile with a version of Unicode that doesn't have the Script property, these extensions won't be defined at all. 💀
(Actually, besides Common, the Inherited script also contains characters that are used in multiple scripts. These are modifier characters which inherit the script value of the controlling character. Some of these are used in many scripts, and so go into Inherited in both Script and Script_Extensions. Others are used in just a few scripts, so they're in Inherited in Script, but not in Script_Extensions.)
It's worth stressing that there are several different sets of digits in Unicode that are equivalent to 0-9 and are matchable by \d in a regular expression. If they're used in a single language only, they're in that language's Script and Script_Extensions. If they're used in more than one script, they'll be in sc=Common, but only if they're used in many scripts should they be in scx=Common.
The explanation above has omitted some detail; refer to UAX#24 "Unicode Script Property": https://www.unicode.org/reports/tr24.
A complete list of scripts and their shortcuts is in perluniprops. 📋
🏷️ Use of the Is Prefix 🏷️
For backward compatibility (with ancient Perl 5.6, our ancestor fr), all properties writable without using the compound form mentioned so far may have Is or Is_ prepended to their name. So \P{Is_Lu}, for example, is equal to \P{Lu}, and \p{IsScript:Arabic} is equal to \p{Arabic}. cute, no cap 💅
🧱 Blocks 🧱
In addition to scripts, Unicode also defines blocks of characters. The difference between scripts and blocks is that the concept of scripts is closer to natural languages, while the concept of blocks is more of an artificial grouping based on groups of Unicode characters with consecutive ordinal values. For example, the Basic Latin block is all the characters whose ordinals are between 0 and 127, inclusive — in other words, the ASCII characters. The Latin script contains some letters from this as well as several other blocks, like Latin-1 Supplement, Latin Extended-A, etc., but it does not contain all the characters from those blocks. It does not, for example, contain the digits 0-9, because those digits are shared across many scripts, and hence are in the Common script.
For more about scripts versus blocks, see UAX#24 "Unicode Script Property": https://www.unicode.org/reports/tr24
The Script_Extensions or Script properties are likely to be the ones you actually want when processing natural language; the Block property may occasionally be useful in working with the nuts and bolts of Unicode.
Block names are matched in the compound form, like \p{Block: Arrows} or \p{Blk=Hebrew}. Unlike most other properties, only a few block names have a Unicode-defined short name.
Perl also defines single form synonyms for the block property in cases where these don't conflict with something else. But don't use any of these, because they are unstable. Since these are Perl extensions, they're subordinate to official Unicode property names; Unicode doesn't know nor care about Perl's extensions. It may happen that a name that currently means the Perl extension will later be changed without warning to mean a different Unicode property in a future version of the perl interpreter that uses a later Unicode release, and your code would no longer work. The extensions are mentioned here for completeness: take the block name and prefix it with one of: In (for example \p{Blk=Arrows} can currently be written as \p{In_Arrows}); or sometimes Is (like \p{Is_Arrows}); or sometimes no prefix at all (\p{Arrows}). As of this writing (Unicode 9.0) there are no conflicts with using the In_ prefix, but there are plenty with the other two forms. For example, \p{Is_Hebrew} and \p{Hebrew} mean \p{Script_Extensions=Hebrew} which is NOT the same thing as \p{Blk=Hebrew}. Our advice used to be to use the In_ prefix as a single form way of specifying a block. But Unicode 8.0 added properties whose names begin with In, and it's now clear that it's only luck that's so far prevented a conflict. Using In is only marginally less typing than Blk:, and the latter's meaning is clearer anyway, and guaranteed to never conflict. So don't take chances. Use \p{Blk=foo} for new code. And be sure that block is what you really really want to do. In most cases scripts are what you want instead. 🙈
A complete list of blocks is in perluniprops.
✨ Other Properties ✨
There are many more properties than the very basic ones described here. A complete list is in perluniprops.
Unicode defines all its properties in the compound form, so all single-form properties are Perl extensions. Most of these are just synonyms for the Unicode ones, but some are genuine extensions, including several that are in the compound form. And quite a few of these are actually recommended by Unicode (in https://www.unicode.org/reports/tr18).
This section gives some details on all extensions that aren't just synonyms for compound-form Unicode properties (for those properties, you'll have to refer to the Unicode Standard https://www.unicode.org/reports/tr44.
\p{All}— This matches every possible code point. It's equivalent toqr/./s. Unlike all the other non-user-defined\p{}property matches, no warning is ever generated if this property is matched against a non-Unicode code point (see "Beyond Unicode code points" below).\p{Alnum}— This matches any\p{Alphabetic}or\p{Decimal_Number}character.\p{Any}— This matches any of the1_114_112Unicode code points. It's a synonym for\p{Unicode}. 👑\p{ASCII}— matches any of the 128 characters in the US-ASCII character set, which is a subset of Unicode. Tiny but mighty 💅\p{Assigned}— matches any assigned code point, meaning any code point whose general category is notUnassigned(or, same thing, notCn). So it's the "this one actually has a job" club 🫶\p{Blank}— literally the same as\hand\p{HorizSpace}: a character that changes the spacing horizontally. Same vibe, three names, iykyk ✨\p{Decomposition_Type: Non_Canonical}(short:\p{Dt=NonCanon}) — matches a character that has any of the non-canonical decomposition types. Canonical decompositions got introduced back up in the "Extended Grapheme Clusters (Logical characters)" section. But tons more characters have a different kind of decomposition, generically called "compatible" decompositions, aka "non-canonical". The sequences that form these decompositions are not considered canonically equivalent to the pre-composed character. Classic example: the "SUPERSCRIPT ONE". It's somewhat like a regular digit 1 but not exactly, and its decomposition into the digit 1 is called a "compatible" decomposition — specifically a "super" (for "superscript") decomposition. There are several such compatibility decompositions (peephttps://www.unicode.org/reports/tr44).\p{Dt: Non_Canon}is a Perl extension that uses just one name to refer to the union of all of them 💫
Most Unicode characters don't have a decomposition at all, so their decomposition type is None. So Non_Canonical is equivalent to:
qr/(?[ \P{DT=Canonical} - \p{DT=None} ])/(Heads up: one of the non-canonical decompositions is named "compat", which honestly could've been better named "miscellaneous". It's just the stuff Unicode couldn't figure out a better generic name for. 😭)
\p{Graph}— matches any character that is graphic. Theoretically that means a character that would make a printer use ink. 🖨️\p{HorizSpace}— same as\hand\p{Blank}: a character that changes the spacing horizontally. Yes bestie, it's the same trio again 🌸\p{In=*}— a synonym for\p{Present_In=*}. Just a shorter outfit for the same thing 👑\p{PerlSpace}— same as\s, but restricted to ASCII, namely[ \f\n\r\t], and starting in Perl v5.18, a vertical tab.
Mnemonic: Perl's (original) space.
\p{PerlWord}— same as\w, restricted to ASCII, namely[A-Za-z0-9_].
Mnemonic: Perl's (original) word.
\p{Posix...}— there are several of these, and they're equivalents, using the\p{}notation, for Posix classes. They're described in "POSIX Character Classes" in perlrecharclass. 🧚\p{Present_In: *}(short:\p{In=*}) — this property is for when you need to know in what Unicode version(s) a character exists.
The * stands for some Unicode version number, like 1.1 or 12.0; or the * can also be Unassigned. This property matches the code points whose final disposition has been settled as of the Unicode release given by that version number; \p{Present_In: Unassigned} matches those code points whose meaning has yet to be assigned.
Example time ✨ U+0041 LATIN CAPITAL LETTER A was present in the very first Unicode release available, which is 1.1, so this property is true for all valid * versions. Meanwhile U+1EFF wasn't assigned until version 5.1, when it became LATIN SMALL LETTER Y WITH LOOP, so the only * values that would match it are 5.1, 5.2, and later. Slay for the late bloomers 🦋
Unicode furnishes the Age property, from which this one is derived. The problem with Age is that a strict interpretation of it (and Perl takes that strict interpretation) has it matching the precise release a code point's meaning is introduced in. So U+0041 would match only 1.1, and U+1EFF only 5.1. That is usually not what you want, bestie 😭
Some non-Perl implementations of the Age property may change its meaning to be the same as the Perl Present_In property; just be aware of that.
Another confusing thing about both these properties: the definition isn't that the code point has been assigned, but that the meaning of the code point has been determined. This is because 66 code points will always be unassigned, and so the Age for them is the Unicode version in which the decision to make them so was made. For example, U+FDD0 is to be permanently unassigned to a character, and the decision to do that was made in version 3.1, so \p{Age=3.1} matches this character — and so does \p{Present_In: 3.1} and up. 📌
\p{Print}— matches any character that is graphical or blank, except controls.\p{SpacePerl}— same as\s, including beyond ASCII.
Mnemonic: Space, as modified by Perl. (It doesn't include the vertical tab until v5.18, which both the Posix standard and Unicode consider white space.)
\p{Title}and\p{Titlecase}— under case-sensitive matching, these both match the same code points as\p{General Category=Titlecase_Letter}(\p{gc=lt}). The difference is that under/icaseless matching, these match the same as\p{Cased}, whereas\p{gc=lt}matches\p{Cased_Letter}. 💅\p{Unicode}— matches any of the1_114_112Unicode code points. It's\p{Any}. The whole entire squad 🌈\p{VertSpace}— same as\v: a character that changes the spacing vertically. ⬆️\p{Word}— same as\w, including over100_000characters beyond ASCII. That's a lot of word, bestie 🔥\p{XPosix...}— there are several of these, and they're the standard Posix classes extended to the full Unicode range. They're described in "POSIX Character Classes" in perlrecharclass.
✨ Comparison of \N{...} and \p{name=...} ✨
Starting in Perl 5.32, you can specify a character by its name in regular expression patterns using \p{name=...}. This is in addition to the longstanding method of using \N{...}. Here's the tea on how these two differ ☕
- can interpolate —
\N{...}: only witheval;\p{Name=...}: yes [1] - custom names —
\N{...}: yes;\p{Name=...}: no [2] - name aliases —
\N{...}: yes;\p{Name=...}: yes [3] - named sequences —
\N{...}: yes;\p{Name=...}: yes [4] - name value parsing —
\N{...}: exact;\p{Name=...}: Unicode loose [5]
[1] Being able to interpolate means you can do something like
qr/\p{na=latin capital letter $which}/and specify $which somewhere else. Very main character of you 💖
[2] You can create your own names for characters, and override official ones when using \N{...}. See "CUSTOM ALIASES" in charnames.
[3] Some characters have multiple names (synonyms).
[4] Some particular sequences of characters are given a single name, in addition to their individual ones.
[5] Exact name value matching means you have to specify case, hyphens, underscores, and spaces precisely in the name you want. Loose matching follows the Unicode rules at https://www.unicode.org/reports/tr44/tr44-24.html#UAX44-LM2, where these are mostly irrelevant. Except for a few outlier character names, these are the same rules as are already used for any other \p{...} property.
🦋 Wildcards in Property Values 🦋
Starting in Perl 5.30, it is possible to do something like this:
qr!\p{numeric_value=/\A[0-5]\z/}!or, by abbreviating and adding /x,
qr! \p{nv= /(?x) \A [0-5] \z / }!This matches all code points whose numeric value is one of 0, 1, 2, 3, 4, or 5. This particular example could instead have been written as
qr! \A [ \p{nv=0}\p{nv=1}\p{nv=2}\p{nv=3}\p{nv=4}\p{nv=5} ] \z !xxin earlier perls, so in this case this feature just makes things easier and shorter to write. If we hadn't included the \A and \z, these would have matched things like 1/2, because that contains a 1 (as well as a 2). As written, it matches things like subscripts that have these numeric values. If we only wanted the decimal digits with those numeric values, we could say,
qr! (?[ \d & \p{nv=/[0-5]/ ]) }!xThe \d gets rid of needing to anchor the pattern, since it forces the result to only match [0-9], and the [0-5] further restricts it. 🎀
The text in the above examples enclosed between the / characters can be just about any regular expression. It's independent of the main pattern, so it doesn't share any capturing groups, etc. The delimiters for it must be ASCII punctuation, but it may NOT be delimited by {, nor }, nor contain a literal }, because that delimits the end of the enclosing \p{}. Like any pattern, certain other delimiters are terminated by their mirror images. These are (, [, and <. If the delimiter is any of -, _, +, or \, or is the same delimiter as is used for the enclosing pattern, it must be preceded by a backslash escape, both fore and aft. 💀
Beware of using$to indicate to match the end of the string. It can too easily be interpreted as being a punctuation variable, like$/. 🙈
No modifiers may follow the final delimiter. Instead, use (?adlupimnsx-imnsx) in perlre and/or (?adluimnsx-imnsx:pattern) in perlre to specify modifiers. However, certain modifiers are illegal in your wildcard subpattern. The only character set modifier specifiable is /aa; any other character set, and -m, and p, and s are all illegal. Specifying modifiers like qr/.../gc that aren't legal in the (?...) notation normally raise a warning, but with wildcard subpatterns, their use is an error. The m modifier is ineffective; everything that matches will be a single line. 😌
By default, your pattern is matched case-insensitively, as if /i had been specified. You can change this by saying (?-i) in your pattern.
There are also certain operations that are illegal. You can't nest \p{...} and \P{...} calls within a wildcard subpattern, and \G doesn't make sense, so it's also prohibited. 🚫
And the * quantifier (or its equivalent (0,}) is illegal.
This feature is not available when the left-hand side is prefixed by Is_, nor for any form that is marked as "Discouraged" in "Discouraged" in perluniprops.
This experimental feature has been added to begin to implement https://www.unicode.org/reports/tr18/#Wildcard_Properties. Using it will raise a (default-on) warning in the experimental::uniprop_wildcards category. We reserve the right to change its operation as we gain experience. ✨🧪
okay so your subpattern can literally be anything, bestie — but for it to actually have some utility, it should match when it's called with either or both of:
- a) the full name of the property value, with underscores (and/or spaces if you're in the Block property) and some stuff uppercase; or
- b) the property value in all lowercase, with spaces and underscores squeezed out.
like, for example:
qr!\p{Blk=/Old I.*/}!
qr!\p{Blk=/oldi.*/}!these two would match the exact same things. 💅
another example, this one showing that inside \p{...} you don't need /x just to have spaces:
qr!\p{scx= /Hebrew|Greek/ }!ngl, to be safe we should have anchored that example above, so it doesn't accidentally match something like Hebrew_Braille — but there aren't any script names like that, so far. 😌
a warning gets issued if none of the legal values for a property are matched by your pattern. and it's likely that a future release will raise a warning if your pattern ends up causing every possible code point to match. so like, watch out for that.
starting in 5.32, the Name, Name Aliases, and Named Sequences properties are allowed to be matched. they're considered a single combination property, just like it's long been the case for \N{}. loose matching doesn't work in exactly the same way for these as it does for the values of other properties. the rules live here: <https://www.unicode.org/reports/tr44/tr44-24.html#UAX44-LM2>. as a result, Perl doesn't try loose matching for you, like it does in other properties. all letters in names are uppercase, but you can add (?i) to your subpattern to ignore case. if you're uncertain where a blank is, you can use ? in your subpattern. no character name contains an underscore, so don't even bother trying to match one. the use of hyphens is particularly problematic; refer to that link up there. but note that, as of Unicode 13.0, the only script in modern usage which has weirdnesses with these is Tibetan; also the two Korean characters U+116C HANGUL JUNGSEONG OE and U+1180 HANGUL JUNGSEONG O-E. Unicode makes no promises to not add hyphen-problematic names in the future. 💀
using wildcards on these is resource intensive, given the hundreds of thousands of legal names that must be checked against.
an example of using Name property wildcards is
qr!\p{name=/(SMILING|GRINNING) FACE/}!another is
qr/(?[ \p{name=\/CJK\/} - \p{ideographic} ])/which is the 200-ish (as of Unicode 13.0) CJK characters that aren't ideographs. 🌸
there are certain properties that wildcard subpatterns don't currently work with. these are:
Bidi Mirroring Glyph
Bidi Paired Bracket
Case Folding
Decomposition Mapping
Equivalent Unified Ideograph
Lowercase Mapping
NFKC Case Fold
Titlecase Mapping
Uppercase Mappingand no, the @unicode_property@ form isn't implemented either. 🙈
here's a complete example of matching IPV4 internet protocol addresses in any (single) script
no warnings 'experimental::uniprop_wildcards';
# Can match a substring, so this intermediate regex needs to have
# context or anchoring in its final use. Using nt=de yields decimal
# digits. When specifying a subset of these, we must include \d to
# prevent things like U+00B2 SUPERSCRIPT TWO from matching
my $zero_through_255 =
qr/ \b (*sr: # All from same script
(?[ \p{nv=0} & \d ])* # Optional leading zeros
( # Then one of:
\d{1,2} # 0 - 99
| (?[ \p{nv=1} & \d ]) \d{2} # 100 - 199
| (?[ \p{nv=2} & \d ])
( (?[ \p{nv=:[0-4]:} & \d ]) \d # 200 - 249
| (?[ \p{nv=5} & \d ])
(?[ \p{nv=:[0-5]:} & \d ]) # 250 - 255
)
)
)
\b
/x;
my $ipv4 = qr/ \A (*sr: $zero_through_255
(?: [.] $zero_through_255 ) {3}
)
\z
/x;✨ User-Defined Character Properties ✨
bestie, you can define your own binary character properties by defining subroutines whose names begin with In or Is. (the regex sets feature (?[ ]) in perlre gives you an alternative that allows more complex definitions, if you're feeling fancy.) the subroutines can be defined in any package. they override any Unicode properties expressed as the same names. the user-defined properties can be used in the regular expression \p{} and \P{} constructs; and if you're using a user-defined property from a package other than the one you're in, you must specify its package in the \p{} or \P{} construct.
# assuming property IsForeign defined in Lang::
package main; # property package name required
if ($txt =~ /\p{Lang::IsForeign}+/) { ... }
package Lang; # property package name not required
if ($txt =~ /\p{IsForeign}+/) { ... }the subroutines are passed a single parameter, which is 0 if case-sensitive matching is in effect and non-zero if caseless matching is in effect. the subroutine may return different values depending on the value of the flag. but the subroutine is never called more than once for each flag value (zero vs non-zero). the return value gets saved and used instead of calling the sub ever again. if the sub is defined at the time the pattern is compiled, it will be called then; if not, it'll be called the first time its value (for that flag) is needed during execution.
note that if the regular expression is tainted, then Perl will die rather than calling the subroutine when the name of the subroutine is determined by the tainted data. 💀
the subroutines must return a specially-formatted string, with one or more newline-separated lines. each line must be one of the following:
- a single hexadecimal number denoting a code point to include.
- two hexadecimal numbers separated by horizontal whitespace (space or tabular characters) denoting a range of code points to include. the second number must not be smaller than the first.
- something to include, prefixed by
+: a built-in character property (prefixed byutf8::) or a fully qualified (including package name) user-defined character property, to represent all the characters in that property; two hexadecimal code points for a range; or a single hexadecimal code point. - something to exclude, prefixed by
-: an existing character property (prefixed byutf8::) or a fully qualified (including package name) user-defined character property, to represent all the characters in that property; two hexadecimal code points for a range; or a single hexadecimal code point. - something to negate, prefixed
!: an existing character property (prefixed byutf8::) or a fully qualified (including package name) user-defined character property, to represent all the characters in that property; two hexadecimal code points for a range; or a single hexadecimal code point. - something to intersect with, prefixed by
&: an existing character property (prefixed byutf8::) or a fully qualified (including package name) user-defined character property, for all the characters except the characters in the property; two hexadecimal code points for a range; or a single hexadecimal code point.
for example, to define a property that covers both the Japanese syllabaries (hiragana and katakana), you can define
sub InKana {
return <<END;
3040\t309F
30A0\t30FF
END
}imagine that the here-doc end marker is at the beginning of the line. now you can use \p{InKana} and \P{InKana}. 🎀
you could also have used the existing block property names:
sub InKana {
return <<'END';
+utf8::InHiragana
+utf8::InKatakana
END
}suppose you wanted to match only the allocated characters, not the raw block ranges — in other words, you want to remove the unassigned characters:
sub InKana {
return <<'END';
+utf8::InHiragana
+utf8::InKatakana
-utf8::IsCn
END
}the negation is useful for defining (surprise!) negated classes.
sub InNotKana {
return <<'END';
!utf8::InHiragana
-utf8::InKatakana
+utf8::IsCn
END
}this will match all non-Unicode code points, since every one of them is not in Kana. you can use intersection to exclude these, if desired, as this modified example shows:
sub InNotKana {
return <<'END';
!utf8::InHiragana
-utf8::InKatakana
+utf8::IsCn
&utf8::Any
END
}&utf8::Any must be the last line in the definition. periodt.
intersection is used generally for getting the common characters matched by two (or more) classes. it's important to remember not to use & for the first set; that would be intersecting with nothing, resulting in an empty set. (similarly using - for the first set does nothing.)
unlike non-user-defined \p{} property matches, no warning is ever generated if these properties are matched against a non-Unicode code point (see "Beyond Unicode code points" below).
✨ User-Defined Case Mappings (for serious hackers only) ✨
this feature has been removed as of Perl 5.16. the CPAN module Unicode::Casing provides better functionality without the drawbacks that this feature had. if you are using a Perl earlier than 5.16, this feature was most fully documented in the 5.14 version of this pod: <http://perldoc.perl.org/5.14.0/perlunicode.html#User-Defined-Case-Mappings-%28for-serious-hackers-only%29>
✨ Character Encodings for Input and Output ✨
see Encode.
✨ Unicode Regular Expression Support Level ✨
the following list of Unicode supported features for regular expressions describes all features currently directly supported by core Perl. the references to "Level N" and the section numbers refer to UTS#18 "Unicode Regular Expressions" <https://www.unicode.org/reports/tr18>, version 18, October 2016.
Level 1 - Basic Unicode Support
RL1.1 Hex Notation - Done [1]
RL1.2 Properties - Done [2]
RL1.2a Compatibility Properties - Done [3]
RL1.3 Subtraction and Intersection - Done [4]
RL1.4 Simple Word Boundaries - Done [5]
RL1.5 Simple Loose Matches - Done [6]
RL1.6 Line Boundaries - Partial [7]
RL1.7 Supplementary Code Points - Done [8][1]— "\N{U+...}" and "\x{...}", bestie. that's the whole vibe.[2]— "\p{...}" and "\P{...}". okay so this is asking for a minimal list of properties, and Perl does support them 🫶. for all the other properties, go peek at R2.7 below.[3]— Perl has "\d" "\D" "\s" "\S" "\w" "\W" "\X" "[:prop:]" "[:^prop:]", plus literally every property listed by <https://www.unicode.org/reports/tr18/#Compatibility_Properties>. they're all described up in "Other Properties" ✨[4]— the regex sets feature "(?[...])", which showed up starting in v5.18, is what accomplishes this. see "(?[ ])" in perlre.[5]— "\b" and "\B" meet most but not all of what's being asked here, but "\b{wb}" and "\B{wb}" fully do, plus the stricter R2.3. slay 💅[6]— heads up: Perl does Full case-folding when matching, not Simple:
like, "U+1F88" is equivalent to "U+1F00 U+03B9", instead of just "U+1F80". this difference really only matters for certain Greek capital letters with certain modifiers: Full case-folding decomposes the letter, while Simple case-folding would just map it to a single character. iykyk 💀
[7]— the reason this counts as only partially implemented is that Perl has "qr/\b{lb}/" and Unicode::LineBreak, and those are conformant with UAX#14 "Unicode Line Breaking Algorithm" <https://www.unicode.org/reports/tr14>. the regex construct gives you default behavior, while the heavier-weight module gives you customizable line breaking 🎀
but Perl treats "\n" as the start- and end-line delimiter, whereas Unicode says more characters should be read that way too.
these ones:
VT U+000B (\v in C)
FF U+000C (\f)
CR U+000D (\r)
NEL U+0085
LS U+2028
PS U+2029"^" and "$" in regex patterns are supposed to match all of these, but nope, they don't 😭. these characters also don't affect "<>", $., and script line numbers, but they should.
also, lines should not be split inside "CRLF" (so there's no empty line sitting between "\r" and "\n"). for "CRLF", try the ":crlf" layer (see PerlIO).
[8]— the UTF-8/UTF-EBDDIC used in Perl allows not only "U+10000" to "U+10FFFF" but also beyond "U+10FFFF". yes really 🦋
✨ Level 2 - Extended Unicode Support ✨
RL2.1 Canonical Equivalents - Retracted [9]
by Unicode
RL2.2 Extended Grapheme Clusters and - Partial [10]
Character Classes with Strings
RL2.3 Default Word Boundaries - Done [11]
RL2.4 Default Case Conversion - Done
RL2.5 Name Properties - Done
RL2.6 Wildcards in Property Values - Partial [12]
RL2.7 Full Properties - Partial [13]
RL2.8 Optional Properties - Partial [14][9]— Unicode rewrote this chunk of UTS#18 to basically say that getting canonical equivalence (see UAX#15 "Unicode Normalization Forms" <https://www.unicode.org/reports/tr15>) is a programmer-level job. so use NFD to write both your regular expressions and the text you're matching them against (you can use Unicode::Normalize for that) 🫶[10]— Perl has "\X" and "\b{gcb}". Unicode retracted their "Grapheme Cluster Mode", and recently added string properties, which Perl does not support yet. someday bestie 😭[11]— see UAX#29 "Unicode Text Segmentation" <https://www.unicode.org/reports/tr29>,[12]— see "Wildcards in Property Values" above.[13]— Perl supports every property in the Unicode Character Database (UCD). it does not yet support the listed properties that come from other Unicode sources.[14]— the only optional property Perl supports is Named Sequence. none of these properties are in the UCD.
✨ Level 3 - Tailored Support ✨
This has been retracted by Unicode. rip bestie 💀
🌈 Unicode Encodings 🌈
okay so Unicode characters get assigned to code points, which are just abstract numbers. and to actually use those numbers, you need encodings. several of them. let's go 💖
- UTF-8 👑
UTF-8 is a variable-length (1 to 4 bytes), byte-order independent encoding. in most of Perl's documentation, including elsewhere in this document, the term "UTF-8" also means "UTF-EBCDIC". but in this section, "UTF-8" refers only to the encoding used on ASCII platforms. it's a superset of 7-bit US-ASCII, so anything encoded in ASCII has the identical representation when it's encoded in UTF-8. iconic behavior honestly ✨
the following table is from Unicode 3.2.
Code Points 1st Byte 2nd Byte 3rd Byte 4th Byte
U+0000..U+007F 00..7F
U+0080..U+07FF * C2..DF 80..BF
U+0800..U+0FFF E0 * A0..BF 80..BF
U+1000..U+CFFF E1..EC 80..BF 80..BF
U+D000..U+D7FF ED 80..9F 80..BF
U+D800..U+DFFF +++++ utf16 surrogates, not legal utf8 +++++
U+E000..U+FFFF EE..EF 80..BF 80..BF
U+10000..U+3FFFF F0 * 90..BF 80..BF 80..BF
U+40000..U+FFFFF F1..F3 80..BF 80..BF 80..BF
U+100000..U+10FFFF F4 80..8F 80..BF 80..BFsee those gaps marked by "" before several of the byte entries up there? those happen because legal UTF-8 avoids non-shortest encodings. like, technically you *could UTF-8-encode a single code point in different ways, but that's explicitly forbidden, and you should always use the shortest possible encoding (and that's exactly what Perl does) 👑
another way to look at it is via bits:
Code Points 1st Byte 2nd Byte 3rd Byte 4th Byte
0aaaaaaa 0aaaaaaa
00000bbbbbaaaaaa 110bbbbb 10aaaaaa
ccccbbbbbbaaaaaa 1110cccc 10bbbbbb 10aaaaaa
00000dddccccccbbbbbbaaaaaa 11110ddd 10cccccc 10bbbbbb 10aaaaaaso as you can see, the continuation bytes all begin with "10", and the leading bits of the start byte tell you how many bytes are in the encoded character. cute, right? 🎀
the original UTF-8 spec allowed up to 6 bytes, so it could encode numbers up to "0x7FFF_FFFF". Perl continues to allow those, and has extended that all the way up to 13 bytes to encode code points up to what fits in a 64-bit word. but heads up: Perl will warn if you output any of these as being non-portable; and under strict UTF-8 input protocols, they're forbidden 🚫. plus, it's now illegal to use a code point larger than what a signed integer variable on your system can hold. on 32-bit ASCII systems, that means "0x7FFF_FFFF" is the legal maximum (much higher on 64-bit systems). no cap.
- UTF-EBCDIC
like UTF-8, but EBCDIC-safe, the same way UTF-8 is ASCII-safe. so all the basic characters (which includes all those that have ASCII equivalents, like "A", "0", "%", etc.) are the same in both EBCDIC and UTF-EBCDIC 🦋
UTF-EBCDIC is used on EBCDIC platforms. it generally needs more bytes to represent a given code point than UTF-8 does; the largest Unicode code points take 5 bytes to represent (instead of 4 in UTF-8), and, extended for 64-bit words, it uses 14 bytes instead of 13 bytes in UTF-8. so yeah, a little chonkier 💅
- UTF-16, UTF-16BE, UTF-16LE, Surrogates, and "BOM"'s (Byte Order Marks)
the following items are mostly for reference and general Unicode knowledge — Perl doesn't use these constructs internally. just so you know 🫶
like UTF-8, UTF-16 is a variable-width encoding, but where UTF-8 uses 8-bit code units, UTF-16 uses 16-bit code units. all code points take up either 2 or 4 bytes in UTF-16: code points "U+0000..U+FFFF" are stored in a single 16-bit unit, and code points "U+10000..U+10FFFF" in two 16-bit units. that latter case uses surrogates — the first 16-bit unit being the high surrogate, and the second being the low surrogate.
surrogates are code points set aside to encode the "U+10000..U+10FFFF" range of Unicode code points in pairs of 16-bit units. the high surrogates are the range "U+D800..U+DBFF" and the low surrogates are the range "U+DC00..U+DFFF". the surrogate encoding is
$hi = ($uni - 0x10000) / 0x400 + 0xD800;
$lo = ($uni - 0x10000) % 0x400 + 0xDC00;and the decoding is
$uni = 0x10000 + ($hi - 0xD800) * 0x400 + ($lo - 0xDC00);because of the 16-bitness, UTF-16 is byte-order dependent. UTF-16 itself can be used for in-memory computations, but if you need storage or transfer, you have to pick either UTF-16BE (big-endian) or UTF-16LE (little-endian). no in-between bestie 😭
which introduces another problem: what if you just know your data is UTF-16 but you don't know which endianness? Byte Order Marks, or "BOM"'s, are the solution 🎀. a special character has been reserved in Unicode to function as a byte order marker: the character with the code point "U+FEFF" is the "BOM".
the trick is that if you read a "BOM", you'll know the byte order, because if it was written on a big-endian platform you'll read the bytes "0xFE 0xFF", but if it was written on a little-endian platform you'll read the bytes "0xFF 0xFE". (and if the originating platform was writing in ASCII platform UTF-8, you'll read the bytes "0xEF 0xBB 0xBF".) so clever 💅
the way this trick works is that the character with the code point "U+FFFE" is not supposed to be in input streams, so the sequence of bytes "0xFF 0xFE" is unambiguously ""BOM", represented in little-endian format" and cannot be "U+FFFE", represented in big-endian format". periodt.
surrogates have no meaning in Unicode outside of their use in pairs to represent other code points. but Perl allows them to be represented individually internally, for example by saying chr(0xD801), so that all code points — not just the ones valid for open interchange — are representable 🦋. Unicode does define semantics for them, like their "General_Category" is "Cs". but because using them is kind of dangerous, Perl will warn (using the warning category "surrogate", which is a sub-category of "utf8") if someone tries to do stuff like take the lower case of one, or match case-insensitively, or output them 😬. (but don't try this on Perls before 5.14.)
- UTF-32, UTF-32BE, UTF-32LE
the UTF-32 family is pretty much like the UTF-16 family, except the units are 32-bit, and therefore the surrogate scheme isn't needed at all. UTF-32 is a fixed-width encoding 👑. the "BOM" signatures are "0x00 0x00 0xFE 0xFF" for BE and "0xFF 0xFE 0x00 0x00" for LE.
- UCS-2, UCS-4
Okay so picking up right where we left off in the encoding lineup 💅
Legacy, fixed-width encodings defined by the ISO 10646 standard. UCS-2 is a 16-bit encoding. Unlike UTF-16, UCS-2 is not extensible beyond U+FFFF, because it does not use surrogates. UCS-4 is a 32-bit encoding, functionally identical to UTF-32 (the only difference being that UCS-4 forbids neither surrogates nor code points larger than 0x10_FFFF).
UTF-7🦋 — a seven-bit safe (non-eight-bit) encoding, which is useful if the transport or storage is not eight-bit safe. Defined by RFC 2152.
🚫 Noncharacter code points 🚫
So there are 66 code points set aside in Unicode as "noncharacter code points". Every last one of them has the Unassigned (Cn) General_Category, and bestie, no character is ever getting assigned to any of them. They are the 32 code points between U+FDD0 and U+FDEF inclusive, plus these 34:
U+FFFE U+FFFF
U+1FFFE U+1FFFF
U+2FFFE U+2FFFF
...
U+EFFFE U+EFFFF
U+FFFFE U+FFFFF
U+10FFFE U+10FFFFUp until Unicode 7.0, the noncharacters were "forbidden for use in open interchange of Unicode text data", so that code processing those streams could use these code points as sentinels that could be mixed in with character data and would always be distinguishable from that data. (Emphasis above and in the next paragraph are added in this document.)
Unicode 7.0 changed the wording so that they are "not recommended for use in open interchange of Unicode text data". The 7.0 Standard goes on to say:
"If a noncharacter is received in open interchange, an application
is not required to interpret it in any way. It is good practice,
however, to recognize it as a noncharacter and to take appropriate
action, such as replacing it with "U+FFFD" replacement character, to
indicate the problem in the text. It is not recommended to simply
delete noncharacter code points from such text, because of the
potential security issues caused by deleting uninterpreted
characters. (See conformance clause C7 in Section 3.2, Conformance
Requirements, and Unicode Technical Report #36, "Unicode Security
Considerations"
<https://www.unicode.org/reports/tr36/#Substituting_for_Ill_Formed_Subsequences>)."This change happened because it turned out various commercial tools — editors, source code control, that whole vibe — had been written so they wouldn't handle program files that used these code points, which effectively precluded their use almost entirely! And that was never the intent. They've always been meant to be usable within an application, or a cooperating set of applications, at will.
If you're writing code — an editor, say — that's supposed to be able to handle any Unicode text data, then you shouldn't be using these code points yourself, and instead allow them in the input. If you need sentinels, they should instead be something that isn't legal Unicode. For UTF-8 data, you can use the bytes 0xC0 and 0xC1 as sentinels, since they never appear in well-formed UTF-8. (There are equivalents for UTF-EBCDIC.) You can also store your Unicode code points in integer variables and use negative values as sentinels.
If you're not writing such a tool, then whether you accept noncharacters as input is up to you (though the Standard recommends that you not). If you do strict input stream checking with Perl, these code points continue to be forbidden. This is to maintain backward compatibility (otherwise potential security holes could open up, as an unsuspecting application that was written assuming the noncharacters would be filtered out before getting to it, could now, without warning, start getting them). To do strict checking, you can use the layer :encoding('UTF-8').
Perl continues to warn (using the warning category nonchar, which is a sub-category of utf8) if an attempt is made to output noncharacters.
🌈 Beyond Unicode code points 🌈
The maximum Unicode code point is U+10FFFF, and Unicode only defines operations on code points up through that. But Perl works on code points up to the maximum permissible signed number available on the platform 😤. However, Perl will not accept these from input streams unless lax rules are being used, and will warn (using the warning category non_unicode, which is a sub-category of utf8) if any are output.
Since Unicode rules are not defined on these code points, if a Unicode-defined operation is done on them, Perl uses what we believe are sensible rules, while generally warning, using the non_unicode category. For example, uc("\x{11_0000}") will generate such a warning, returning the input parameter as its result, since Perl defines the uppercase of every non-Unicode code point to be the code point itself. (All the case changing operations, not just uppercasing, work this way.)
The situation with matching Unicode properties in regular expressions — the \p{} and \P{} constructs — against these code points is not as clear cut, and how these are handled has changed as we've gained experience.
One possibility is to treat any match against these code points as undefined. But since Perl doesn't have the concept of a match being undefined, it converts this to failing or FALSE. This is almost, but not quite, what Perl did from v5.14 (when use of these code points became generally reliable) through v5.18. The difference is that Perl treated all \p{} matches as failing, but all \P{} matches as succeeding.
One problem with this is that it leads to unexpected, and confusing results in some cases:
chr(0x110000) =~ \p{ASCII_Hex_Digit=True} # Failed on <= v5.18
chr(0x110000) =~ \p{ASCII_Hex_Digit=False} # Failed! on <= v5.18That is, it treated both matches as undefined, and converted that to false (raising a warning on each). The first case is the expected result, but the second is likely counterintuitive: "How could both be false when they are complements?" Another problem was that the implementation optimized many Unicode property matches down to already existing simpler, faster operations, which don't raise the warning. We chose to not forgo those optimizations — which help the vast majority of matches — just to generate a warning for the unlikely event that an above-Unicode code point is being matched against.
As a result of these problems, starting in v5.20, what Perl does is to treat non-Unicode code points as just typical unassigned Unicode characters, and matches accordingly. (Note: Unicode has atypical unassigned code points. For example, it has noncharacter code points, and ones that, when they do get assigned, are destined to be written Right-to-left, as Arabic and Hebrew are. Perl assumes that no non-Unicode code point has any atypical properties.)
Perl, in most cases, will raise a warning when matching an above-Unicode code point against a Unicode property when the result is TRUE for \p{}, and FALSE for \P{}. For example:
chr(0x110000) =~ \p{ASCII_Hex_Digit=True} # Fails, no warning
chr(0x110000) =~ \p{ASCII_Hex_Digit=False} # Succeeds, with warningIn both these examples, the character being matched is non-Unicode, so Unicode doesn't define how it should match. It clearly isn't an ASCII hex digit, so the first example clearly should fail, and so it does, with no warning. But it is arguable that the second example should have an undefined, hence FALSE, result. So a warning is raised for it.
Thus the warning is raised for many fewer cases than in earlier Perls, and only when what the result is could be arguable. It turns out that none of the optimizations made by Perl (or are ever likely to be made) cause the warning to be skipped, so it solves both problems of Perl's earlier approach. The most commonly used property that is affected by this change is \p{Unassigned} which is a short form for \p{General_Category=Unassigned}. Starting in v5.20, all non-Unicode code points are considered Unassigned. In earlier releases the matches failed because the result was considered undefined.
The only place where the warning is not raised when it might ought to have been is if optimizations cause the whole pattern match to not even be attempted. For example, Perl may figure out that for a string to match a certain regular expression pattern, the string has to contain the substring foobar. Before attempting the match, Perl may look for that substring, and if not found, immediately fail the match without actually trying it; so no warning gets generated even if the string contains an above-Unicode code point.
This behavior is more "Do what I mean" than in earlier Perls for most applications. But it catches fewer issues for code that needs to be strictly Unicode compliant. Therefore there is an additional mode of operation available to accommodate such code. This mode is enabled if a regular expression pattern is compiled within the lexical scope where the non_unicode warning class has been made fatal, say by:
use warnings FATAL => "non_unicode"(see warnings). In this mode of operation, Perl will raise the warning for all matches against a non-Unicode code point (not just the arguable ones), and it skips the optimizations that might cause the warning to not be output. (It currently still won't warn if the match isn't even attempted, like in the foobar example above.)
In summary, Perl now normally treats non-Unicode code points as typical Unicode unassigned code points for regular expression matches, raising a warning only when it is arguable what the result should be. However, if this warning has been made fatal, it isn't skipped.
There is one exception to all this. \p{All} looks like a Unicode property, but it is a Perl extension that is defined to be true for all possible code points, Unicode or not, so no warning is ever generated when matching this against a non-Unicode code point. (Prior to v5.20, it was an exact synonym for \p{Any}, matching code points 0 through 0x10FFFF.)
🔒 Security Implications of Unicode 🔒
First, read Unicode Security Considerations <https://www.unicode.org/reports/tr36>.
Also, note the following:
- Malformed UTF-8 💀
UTF-8 is very structured, so many combinations of bytes are invalid. In the past, Perl tried to soldier on and make some sense of invalid combinations, but this can lead to security holes, so now, if the Perl core needs to process an invalid combination, it will either raise a fatal error, or will replace those bytes by the sequence that forms the Unicode REPLACEMENT CHARACTER, for which purpose Unicode created it.
Every code point can be represented by more than one possible syntactically valid UTF-8 sequence. Back in the day, both Unicode and Perl were like "yeah sure, all of these are valid 💖" — but now? Every sequence that's longer than the shortest possible one is considered malformed. Periodt. 💅
Unicode considers a whole bunch of code points to be illegal, or at least to be avoided 👀. Perl generally just... accepts them anyway, once they've made it through whatever input filters might be trying to exclude them. We already talked about these up above (peep "Surrogates" under UTF-16 in "Unicode Encodings", "Noncharacter code points", and "Beyond Unicode code points").
- Regular expression pattern matching may genuinely surprise you if you're not accustomed to Unicode. Starting in Perl 5.14, several pattern modifiers became available to control this, and they're called the character set modifiers ✨. All the details live in "Character set modifiers" in perlre.
As discussed elsewhere, Perl has one foot (two hooves? 🐴) planted in each of two worlds: the old world of ASCII and single-byte locales, and the new world of Unicode — and it upgrades whenever necessary. But bestie, listen: if your legacy code does not explicitly use Unicode, then no automatic switch-over to Unicode should happen. No surprise glow-ups. 🫶
Unicode in Perl on EBCDIC 🌈
Unicode is supported on EBCDIC platforms. See perlebcdic.
Unless ASCII vs. EBCDIC issues are specifically being discussed, references to UTF-8 encoding in this document and elsewhere should be read as meaning UTF-EBCDIC on EBCDIC platforms. See "Unicode and UTF" in perlebcdic.
Because UTF-EBCDIC is so similar to UTF-8, the differences are mostly hidden from you 🫣; use utf8 (and NOT something like use utfebcdic — that's not a thing, don't do it) declares the script is in the platform's "native" 8-bit encoding of Unicode. (Same energy for the :utf8 layer.)
Locales 🌍
See "Unicode and UTF-8" in perllocale
When Unicode Does Not Happen 😭
There are still so many places where Unicode (in some encoding or another) could be given as arguments or received as results, or both, in Perl — but it just... isn't. Even though Perl has extensive ways to input and output in Unicode, and a few other "entry points" like the @ARGV array (which can sometimes be interpreted as UTF-8).
The following are such interfaces. Also, see "The "Unicode Bug"". For all of these interfaces Perl currently (as of v5.16.0) simply assumes byte strings both as arguments and results, or UTF-8 strings if the (deprecated 😬) encoding pragma has been used.
One reason Perl doesn't even attempt to resolve the role of Unicode in these situations is that the answers are highly dependent on the operating system and the file system(s). Like, whether filenames can be in Unicode and in exactly what kind of encoding — that is not exactly a portable concept, bestie. Same deal for qx and system: how well will the "command-line interface" (and which of them?) handle Unicode? 🤷♀️
chdir,chmod,chown,chroot,exec,link,lstat,mkdir,rename,rmdir,stat,symlink,truncate,unlink,utime,-X%ENVglob(aka the<*>)open,opendir,sysopenqx(aka the backtick operator),systemreaddir,readlink
The "Unicode Bug" 💀
The term "Unicode bug" has been applied to an inconsistency with the code points in the "Latin-1 Supplement" block — that is, between 128 and 255. Without a locale specified, unlike all other characters or code points, these characters can have very different semantics depending on the rules in effect. (Characters whose code points are above 255 force Unicode rules; whereas the rules for ASCII characters are the same under both ASCII and Unicode rules.)
Under Unicode rules, these upper-Latin1 characters are interpreted as Unicode code points, which means they have the same semantics as Latin-1 (ISO-8859-1) and C1 controls.
As explained in "ASCII Rules versus Unicode Rules", under ASCII rules, they are considered to be unassigned characters.
This can lead to unexpected results 😳. For example, a string's semantics can suddenly change if a code point above 255 is appended to it, which flips the rules from ASCII to Unicode. As an example, consider the following program and its output:
$ perl -le'
no feature "unicode_strings";
$s1 = "\xC2";
$s2 = "\x{2660}";
for ($s1, $s2, $s1.$s2) {
print /\w/ || 0;
}
'
0
0
1If there's no \w in s1 nor in s2, why does their concatenation have one? 🤔
This anomaly stems from Perl's attempt to not disturb older programs that didn't use Unicode, along with Perl's desire to add Unicode support seamlessly. But the result turned out to not be seamless. (By the way, you can choose to be warned when things like this happen. See "encoding::warnings".)
use feature 'unicode_strings' was added, starting in Perl v5.12, to address this problem. It affects these things:
- Changing the case of a scalar — that is, using
uc(),ucfirst(),lc(), andlcfirst(), or\L,\U,\uand\lin double-quotish contexts, such as regular expression substitutions.
Under unicode_strings starting in Perl 5.12.0, Unicode rules are generally used. See "lc" in perlfunc for details on how this works in combination with various other pragmas.
- Using caseless (
/i) regular expression matching.
Starting in Perl 5.14.0, regular expressions compiled within the scope of unicode_strings use Unicode rules even when executed or compiled into larger regular expressions outside the scope. ✨
- Matching any of several properties in regular expressions.
These properties are \b (without braces), \B (without braces), \s, \S, \w, \W, and all the Posix character classes except [[:ascii:]].
Starting in Perl 5.14.0, regular expressions compiled within the scope of unicode_strings use Unicode rules even when executed or compiled into larger regular expressions outside the scope.
- In
quotemetaor its inline equivalent\Q.
Starting in Perl 5.16.0, consistent quoting rules are used within the scope of unicode_strings, as described in "quotemeta" in perlfunc. Prior to that, or outside its scope, no code points above 127 are quoted in UTF-8 encoded strings, but in byte encoded strings, code points between 128-255 are always quoted.
- In the
..or range operator.
Starting in Perl 5.26.0, the range operator on strings treats their lengths consistently within the scope of unicode_strings. Prior to that, or outside its scope, it could produce strings whose length in characters exceeded that of the right-hand side, where the right-hand side took up more bytes than the correct range endpoint. 😵💫
- In
split's special-case whitespace splitting.
Starting in Perl 5.28.0, the split function with a pattern specified as a string containing a single space handles whitespace characters consistently within the scope of unicode_strings. Prior to that, or outside its scope, characters that are whitespace according to Unicode rules but not according to ASCII rules were treated as field contents rather than field separators when they appear in byte-encoded strings.
You can see from the above that the effect of unicode_strings increased over several Perl releases 📈. (And Perl's support for Unicode continues to improve; it's best to use the latest available release in order to get the most complete and accurate results possible.) Note that unicode_strings is automatically chosen if you use v5.12 or higher. 👑
For Perls earlier than those described above, or when a string is passed to a function outside the scope of unicode_strings, see the next section.
Forcing Unicode in Perl (Or Unforcing Unicode in Perl) 💪
Sometimes (see "When Unicode Does Not Happen" or "The "Unicode Bug"") there are situations where you simply need to force a byte string into UTF-8, or vice versa. The standard module Encode can be used for this, or the low-level calls utf8::upgrade($bytestring) and "utf8::downgrade($utf8string[, FAIL_OK])".
Note that utf8::downgrade() can fail if the string contains characters that don't fit into a byte. 😬
Calling either function on a string that already is in the desired state is a no-op. Chill. Nothing happens. 🧘♀️
"ASCII Rules versus Unicode Rules" gives all the ways that a string is made to use Unicode rules.
Using Unicode in XS 🦋
See "Unicode Support" in perlguts for an introduction to Unicode at the XS level, and "Unicode Support" in perlapi for the API details.
Hacking Perl to work on earlier Unicode versions (for very serious hackers only) 🧙♀️
Perl by default comes with the latest supported Unicode version built-in, but the goal is to allow you to change to use any earlier one. In Perls v5.20 and v5.22, however, the earliest usable version is Unicode 5.1. Perl v5.18 and v5.24 are able to handle all earlier versions.
Download the files in the desired version of Unicode from the Unicode web site <https://www.unicode.org>). These should replace the existing files in lib/unicore in the Perl source tree. Follow the instructions in README.perl in that directory to change some of their names, and then build perl (see INSTALL).
Porting code from perl-5.6.X 🕰️
Perls starting in 5.8 have a different Unicode model from 5.6. In 5.6 the programmer was required to use the utf8 pragma to declare that a given scope expected to deal with Unicode data and had to make sure that only Unicode data were reaching that scope. If you have code that is working with 5.6, you will need some of the following adjustments to your code. The examples are written such that the code will continue to work under 5.6, so you should be safe to try them out. 🫶
- A filehandle that should read or write UTF-8
if ($] > 5.008) {
binmode $fh, ":encoding(UTF-8)";
}- A scalar that is going to be passed to some extension
Be it Compress::Zlib, Apache::Request or any extension that has no mention of Unicode in the manpage, you need to make sure that the UTF8 flag is stripped off. Note that at the time of this writing (January 2012) the mentioned modules are not UTF-8-aware. Please check the documentation to verify if this is still true.
if ($] > 5.008) {
require Encode;
$val = Encode::encode("UTF-8", $val); # make octets
}- A scalar we got back from an extension
If you believe the scalar comes back as UTF-8, you will most likely want the UTF8 flag restored:
if ($] > 5.008) {
require Encode;
$val = Encode::decode("UTF-8", $val);
}- Same thing, if you are really sure it is UTF-8
if ($] > 5.008) {
require Encode;
Encode::_utf8_on($val);
}- A wrapper for DBI
fetchrow_arrayandfetchrow_hashref— okay bestie, so when your database is serving nothing but UTF-8, writing a little wrapper function (or method) is the ✨convenient✨ way to swap out all yourfetchrow_arrayandfetchrow_hashrefcalls in one go. A wrapper function also makes it way easier to adapt later when your database driver levels up. Heads up though: at the time of this writing (January 2012), the DBI has no standardized way to deal with UTF-8 data. So pls go check the DBI documentation to verify if that's still true. 👀
sub fetchrow {
# $what is one of fetchrow_{array,hashref}
my($self, $sth, $what) = @_;
if ($] < 5.008) {
return $sth->$what;
} else {
require Encode;
if (wantarray) {
my @arr = $sth->$what;
for (@arr) {
defined && /[^\000-\177]/ && Encode::_utf8_on($_);
}
return @arr;
} else {
my $ret = $sth->$what;
if (ref $ret) {
for my $k (keys %$ret) {
defined
&& /[^\000-\177]/
&& Encode::_utf8_on($_) for $ret->{$k};
}
return $ret;
} else {
defined && /[^\000-\177]/ && Encode::_utf8_on($_) for $ret;
return $ret;
}
}
}
}- A large scalar that you know can only contain ASCII — ngl, scalars that hold only ASCII but are marked as UTF-8 are sometimes just a whole drag on your program 😩. If you clock that situation, literally just yeet the UTF8 flag off:
utf8::downgrade($val) if $] > 5.008;🐛 BUGS 🐛
Also see "The "Unicode Bug"" up above, bestie. It's still giving chaos.
🌸 Interaction with Extensions 🌸
When Perl trades data with an extension, that extension should be able to understand the UTF8 flag and act accordingly. And if the extension doesn't recognize that flag? Yeah, it's probably gonna hand you back incorrectly-flagged data. 💀
So if you're working with Unicode data, pls consult the documentation of every single module you're using to see if there are any issues with Unicode data exchange. And if the docs don't mention Unicode at all? Suspect the worst, and honestly probably go read the source to learn how the module is actually implemented. 🔍
Modules written completely in Perl shouldn't cause problems. Modules that directly or indirectly touch code written in other programming languages? Those are at risk. No cap.
For the affected functions, the simple strategy to dodge data corruption is to always make the encoding of the exchanged data explicit. Choose an encoding you know the extension can handle. Convert the arguments you pass to the extensions into that encoding, and convert the results back out of that encoding. Write wrapper functions that do the conversions for you, so that later — when the extension finally catches up — you can just change the functions. 💅
To provide an example, let's say the popular Foo::Bar::escape_html function doesn't deal with Unicode data yet. The wrapper function would convert the argument to raw UTF-8 and convert the result back to Perl's internal representation like so:
sub my_escape_html ($) {
my($what) = shift;
return unless defined $what;
Encode::decode("UTF-8", Foo::Bar::escape_html(
Encode::encode("UTF-8", $what)));
}Sometimes, when the extension doesn't convert data but just stores and retrieves it, you'll be able to use the otherwise dangerous Encode::_utf8_on() function. Let's say the popular Foo::Bar extension, written in C, provides a param method that lets you store and retrieve data according to these prototypes:
$self->param($name, $value); # set a scalar
$value = $self->param($name); # retrieve a scalarIf it doesn't yet provide support for any encoding, one could write a derived class with such a param method:
sub param {
my($self,$name,$value) = @_;
utf8::upgrade($name); # make sure it is UTF-8 encoded
if (defined $value) {
utf8::upgrade($value); # make sure it is UTF-8 encoded
return $self->SUPER::param($name,$value);
} else {
my $ret = $self->SUPER::param($name);
Encode::_utf8_on($ret); # we know, it is UTF-8 encoded
return $ret;
}
}Some extensions provide filters on data entry/exit points, like DB_File::filter_store_key and family. 👑 Keep an eye out for those filters in the documentation of your extensions — they can make the transition to Unicode data so much easier.
⚡ Speed ⚡
Okay so here's the tea: some functions are slower when they're working on UTF-8 encoded strings than on byte encoded strings. Every function that has to hop over characters — things like length(), substr() or index() — or that matches regular expressions, can work much faster when the underlying data are byte-encoded. 🏃♀️💨
In Perl 5.8.0 the slowness was often quite spectacular. In Perl 5.8.1 a caching scheme was introduced which improved the situation. But in general, operations with UTF-8 encoded strings are still slower. As an example: the Unicode properties (character classes) like \p{Nd} are known to be quite a bit slower (5-20 times) than their simpler counterparts like [0-9] — then again, there are hundreds of Unicode characters matching Nd compared with the 10 ASCII characters matching [0-9]. So like… fair. 🤷♀️
👀 SEE ALSO 👀
perlunitutperluniintroperlunipropsEncodeopenutf8bytesperlretut"${^UNICODE}" in perlvar- <https://www.unicode.org/reports/tr44>
And that's a wrap, bestie!! 🎀✨ This whole thing is from perl v5.42.3, dated 2026-08-03, and it's the PERLUNICODE(1) page — go forth and encode responsibly, ily 💖🦋
📦 where this page comes from
- fedora 43: perl-doc 5.42.3-524.fc43 · (GPL-1.0-or-later OR Artistic-1.0-Perl) AND Unicode-3.0 AND LicenseRef-Fedora-UltraPermissive
- fedora 44: perl-doc 5.42.3-525.fc44 · (GPL-1.0-or-later OR Artistic-1.0-Perl) AND Unicode-3.0 AND LicenseRef-Fedora-UltraPermissive
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