perlunicode - Unicode support in Perl
If you haven't already, before reading this document, you should become familiar with both perlunitut and perluniintro.
Unicode aims to UNI-fy the en-CODE-ings of all the world's character sets into a single Standard. For quite a few of the various coding standards that existed when Unicode was first created, converting from each to Unicode essentially meant adding a constant to each code point in the original standard, and converting back meant just subtracting that same constant. For ASCII and ISO-8859-1, the constant is 0. For ISO-8859-5, (Cyrillic) the constant is 864; for Hebrew (ISO-8859-8), it's 1488; Thai (ISO-8859-11), 3424; and so forth. This made it easy to do the conversions, and facilitated the adoption of Unicode.
And it worked; nowadays, those legacy standards are rarely used. Most everyone uses Unicode.
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.
Even though some of this section may not be understandable to you on first reading, we think it's important enough to highlight some of the gotchas before delving 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, the use of Unicode may present security issues that aren't obvious, see "Security Implications of Unicode" below.
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.
Use the :encoding(...) layer to read from and write to filehandles using the specified encoding. (See open.)
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 scriptsIf 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.
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.
Before Unicode, most encodings used 8 bits (a single byte) to encode each character. Thus a character was a byte, and a byte was a character, and there could be only 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 that a character may require more than a single byte to represent it, and so the two terms are no longer equivalent. What matter are the characters as whole entities, and not usually the bytes that comprise them. That's what the term "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 include chop(), chomp(), substr(), pos(), index(), rindex(), sort(), sprintf(), and write().
The exceptions are:
the bit-oriented vec
the byte-oriented pack/unpack "C" format
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 bytes pragma
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() and ord() 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 the tr///CU functionality has been removed. For similar functionality to that, see pack('U0', ...) and pack('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 above 0xFF. 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 use utf8::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".
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 v5.12 or higher
This implicitly turns on use feature 'unicode_strings'.
Within the scope of use locale 'not_characters', or use locale and 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.
Note that uc(), or \U in interpolated strings, translates to uppercase, while ucfirst, or \u in interpolated strings, translates to titlecase in languages that make the distinction (which is equivalent to uppercase in languages without the distinction).
There is a CPAN module, Unicode::Casing, which allows you to define your own mappings to be used in lc(), lcfirst(), uc(), ucfirst(), and fc (or their double-quoted string inlined versions such as \U). (Prior to Perl 5.16, this functionality was partially provided in the Perl core, but suffered from a number of insurmountable drawbacks, so the CPAN module was written instead.)
Character classes in regular expressions match based on the character properties specified in the Unicode properties database.
\w can be used to match a Japanese ideograph, for instance; and [[:digit:]] a Bengali number.
Named Unicode properties, scripts, and block ranges may be used (like bracketed character classes) by using the \p{} "matches property" construct and the \P{} negation, "doesn't match property".
See "Unicode Character Properties" for more details.
You can define your own character properties and use them in the regular expression with the \p{} or \P{} construct. See "User-Defined Character Properties" for more details.
Consider a character, say H. It could appear with various marks around it, such as an acute accent, or a circumflex, or various hooks, circles, arrows, etc., above, below, to one side or the other, etc. There are many possibilities among the world's languages. The number of combinations is astronomical, and if there were a character for each combination, it would soon exhaust Unicode's more than a million possible characters. So Unicode took a different approach: there is a character for the base H, and a character for each of the possible marks, and these can be variously combined to get a final logical character. So a logical character--what appears to be a single character--can be a sequence of more than one individual characters. The Unicode standard calls these "extended grapheme clusters" (which is an improved version of the no-longer much used "grapheme cluster"); Perl furnishes the \X regular expression construct to match such sequences in their entirety.
But Unicode's intent is to unify the existing character set standards and practices, and several pre-existing standards have single characters that mean the same thing as some of these combinations, like ISO-8859-1, which has quite a few of them. For example, "LATIN CAPITAL LETTER E WITH ACUTE" was already in this standard when Unicode came along. Unicode therefore added it to its repertoire as that single character. But this character is considered by Unicode to be equivalent to the sequence consisting 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" and the "COMBINING ACCENT" sequence is called canonical equivalence. All pre-composed characters are said to have a decomposition (into the equivalent sequence), and the decomposition type is also called canonical. A string may be comprised as much as possible of precomposed characters, or it may be comprised of entirely decomposed characters. Unicode calls these respectively, "Normalization Form Composed" (NFC) and "Normalization Form Decomposed". The Unicode::Normalize module contains functions that convert between the two. A string may also have both composed characters and decomposed characters; this module can be used to make it all one or the other.
You may be presented with strings in any of these equivalent forms. There is currently nothing in Perl 5 that ignores the differences. So you'll have to specially handle it. The usual advice is to convert your inputs to NFD before processing further.
For more detailed information, see http://unicode.org/reports/tr15/.
(The only time that Perl considers a sequence of individual code points as a single logical character is in the \X construct, already mentioned above. Therefore "character" in this discussion means a single Unicode code point.)
Very nearly all Unicode character properties are accessible through regular expressions by using the \p{} "matches property" construct and the \P{} "doesn't match property" for its negation.
For instance, \p{Uppercase} matches any single character with the Unicode "Uppercase" property, while \p{L} matches any character with a General_Category of "L" (letter) property (see "General_Category" below). Brackets are not required for single letter property names, so \p{L} is equivalent to \pL.
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, and they could have been written as \p{Uppercase=True} and \p{Uppercase=False}, respectively.
This formality is needed when properties are not binary; that is, if 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, such as Left, Right, Whitespace, and others. To match these, one needs to specify both the property name (Bidi_Class), AND the value being matched against (Left, Right, etc.). This is done, as in the examples above, by having the two components separated by an equal sign (or interchangeably, a colon), like \p{Bidi_Class: Left}.
All Unicode-defined character properties may be written in these compound forms of \p{property=value} or \p{property:value}, but Perl provides some additional properties that are written only in the single form, as well as single-form short-cuts for all binary properties and certain others described below, in which you may omit the property name and the equals or colon separator.
Most Unicode character properties have at least two synonyms (or aliases if you prefer): a short one that is easier to type and a longer one that is more descriptive and hence easier to understand. Thus the "L" and "Letter" properties above are equivalent and can be used interchangeably. Likewise, "Upper" is a synonym for "Uppercase", and we could have written \p{Uppercase} equivalently as \p{Upper}. Also, there are typically various synonyms for the values the property can be. For binary properties, "True" has 3 synonyms: "T", "Yes", and "Y"; and "False" has correspondingly "F", "No", and "N". But be careful. A short form of a value for one property may not mean the same thing as the short form spelled the same for another. Thus, for the "General_Category" property, "L" means "Letter", but for the Bidi_Class property, "L" means "Left". A complete list of properties and synonyms is in perluniprops.
Upper/lower case differences in property names and values are irrelevant; thus \p{Upper} means the same thing as \p{upper} or even \p{UpPeR}. Similarly, you can add or subtract underscores anywhere in the middle of a word, so that these are also equivalent to \p{U_p_p_e_r}. And white space is generally irrelevant adjacent to non-word characters, such as the braces and the equals or colon separators, so \p{ Upper } and \p{ Upper_case : Y } are equivalent to these as well. In fact, white space and even hyphens can usually be added or deleted anywhere. So even \p{ Up-per case = Yes} is equivalent. All this is called "loose-matching" by Unicode. The "name" property has some restrictions on this due to a few outlier names. Full details are given in https://www.unicode.org/reports/tr44/tr44-24.html#UAX44-LM2.
The few places where stricter matching is used is in the middle of numbers, the "name" property, and in the Perl extension properties that begin or end with an underscore. Stricter matching 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 introducing a caret (^) between the first brace and the property name: \p{^Tamil} is equal to \P{Tamil}.
Almost all properties are immune to case-insensitive matching. That is, adding a /i regular expression modifier does not change what they match. 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 /i matching. And the second set is Uppercase, Lowercase, and Titlecase, all of which match Cased under /i matching. This set also includes its subsets PosixUpper and PosixLower both of which under /i match PosixAlpha. (The difference between these sets is that some things, such as Roman numerals, come in both upper and lower case so they are Cased, but aren't considered letters, so they aren't Cased_Letter's.)
See "Beyond Unicode code points" for special considerations when matching Unicode properties against non-Unicode code points.
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 furnishes shortcuts in which everything up through the equal or colon separator is omitted. So you can instead just write \pN.
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_Punctuation
S Symbol
Sm Math_Symbol
Sc Currency_Symbol
Sk Modifier_Symbol
So Other_Symbol
Z Separator
Zs Space_Separator
Zl Line_Separator
Zp Paragraph_Separator
C Other
Cc Control (also Cntrl)
Cf Format
Cs Surrogate
Co Private_Use
Cn UnassignedSingle-letter properties match all characters in any of the two-letter sub-properties starting with the same letter. LC and L& are special: both are aliases for the set consisting of everything matched by Ll, Lu, and Lt.
Because scripts differ in their directionality (Hebrew and Arabic are written right to left, for example) Unicode supplies a Bidi_Class property. Some of the values this property can have are:
Value Meaning
L Left-to-Right
LRE Left-to-Right Embedding
LRO Left-to-Right Override
R Right-to-Left
AL Arabic Letter
RLE Right-to-Left Embedding
RLO Right-to-Left Override
PDF Pop Directional Format
EN European Number
ES European Separator
ET European Terminator
AN Arabic Number
CS Common Separator
NSM Non-Spacing Mark
BN Boundary Neutral
B Paragraph Separator
S Segment Separator
WS Whitespace
ON Other NeutralsThis property is always written in the compound form. For example, \p{Bidi_Class:R} matches characters that are normally written right to left. Unlike the "General_Category" property, this property can have more values added in a future Unicode release. Those listed above comprised the complete set for many Unicode releases, but others were 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.
The world's languages are written in many different scripts. This sentence (unless you're reading it in translation) is written in Latin, while Russian is written in Cyrillic, and Greek is written in, well, Greek; Japanese mainly in Hiragana or Katakana. There are many more.
The Unicode Script and Script_Extensions properties give what script a given character is in. The Script_Extensions property is an improved version of Script, as demonstrated 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}). In addition, Perl furnishes shortcuts for all Script_Extensions property names. You can omit everything up through the equals (or colon), and simply write \p{Latin} or \P{Cyrillic}. (This is not true for Script, which is required to be written in the compound form. Prior to Perl v5.26, the single form returned the plain old Script version, but was changed because Script_Extensions gives better results.)
The difference between these two properties involves characters that are used in multiple scripts. For example the digits '0' through '9' are used in many parts of the world. These are placed in a script named Common. Other characters are used in just 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 places all characters that are used in multiple scripts in the Common script, while the Script_Extensions property places those that are used in only a few scripts into each of those scripts; while still using Common for those used in many scripts. Thus both 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} # MatchesScript_Extensions is thus an improved Script, in which there are fewer characters in the Common script, and correspondingly more in other scripts. It is new in Unicode version 6.0, and 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. If you compile with a version of Unicode that doesn't have the Script property, these extensions will not be defined at all.
(Actually, besides Common, the Inherited script, 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 are in Inherited in Script, but not in Script_Extensions.)
It is 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 are used in a single language only, they are in that language's Script and Script_Extensions. If they are used in more than one script, they will be in sc=Common, but only if they are 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.
"Is" PrefixFor backward compatibility (with ancient Perl 5.6), 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}.
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 want to use 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 do not conflict with something else. But don't use any of these, because they are unstable. Since these are Perl extensions, they are 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.
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.
\p{All}This matches every possible code point. It is equivalent to qr/./s. Unlike all the other non-user-defined \p{} property matches, no warning is ever generated if this is 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 the 1_114_112 Unicode code points. It is a synonym for \p{Unicode}.
\p{ASCII}This matches any of the 128 characters in the US-ASCII character set, which is a subset of Unicode.
\p{Assigned}This matches any assigned code point; that is, any code point whose general category is not Unassigned (or equivalently, not Cn).
\p{Blank}This is the same as \h and \p{HorizSpace}: A character that changes the spacing horizontally.
\p{Decomposition_Type: Non_Canonical} (Short: \p{Dt=NonCanon})Matches a character that has any of the non-canonical decomposition types. Canonical decompositions are introduced in the "Extended Grapheme Clusters (Logical characters)" section above. However, many more characters have a different type of decomposition, generically called "compatible" decompositions, or "non-canonical". The sequences that form these decompositions are not considered canonically equivalent to the pre-composed character. An example is the "SUPERSCRIPT ONE". It is somewhat like a regular digit 1, but not exactly; its decomposition into the digit 1 is called a "compatible" decomposition, specifically a "super" (for "superscript") decomposition. There are several such compatibility decompositions (see https://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, so their decomposition type is "None". Hence, Non_Canonical is equivalent to
qr/(?[ \P{DT=Canonical} - \p{DT=None} ])/(Note that one of the non-canonical decompositions is named "compat", which could perhaps have been better named "miscellaneous". It includes just the things that Unicode couldn't figure out a better generic name for.)
\p{Graph}Matches any character that is graphic. Theoretically, this means a character that on a printer would cause ink to be used.
\p{HorizSpace}This is the same as \h and \p{Blank}: a character that changes the spacing horizontally.
\p{In=*}This is a synonym for \p{Present_In=*}
\p{PerlSpace}This is the same as \s, restricted to ASCII, namely [ \f\n\r\t] and starting in Perl v5.18, a vertical tab.
Mnemonic: Perl's (original) space
\p{PerlWord}This is the same as \w, restricted to ASCII, namely [A-Za-z0-9_]
Mnemonic: Perl's (original) word.
\p{Posix...}There are several of these, which are equivalents, using the \p{} notation, for Posix classes and are described in "POSIX Character Classes" in perlrecharclass.
\p{Present_In: *} (Short: \p{In=*})This property is used when you need to know in what Unicode version(s) a character is.
The "*" above stands for some Unicode version number, such as 1.1 or 12.0; or the "*" can also be Unassigned. This property will match the code points whose final disposition has been settled as of the Unicode release given by the version number; \p{Present_In: Unassigned} will match those code points whose meaning has yet to be assigned.
For example, 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. On the other hand, U+1EFF was not assigned until version 5.1 when it became "LATIN SMALL LETTER Y WITH LOOP", so the only "*" that would match it are 5.1, 5.2, and later.
Unicode furnishes the Age property from which this is derived. The problem with Age is that a strict interpretation of it (which Perl takes) has it matching the precise release a code point's meaning is introduced in. Thus U+0041 would match only 1.1; and U+1EFF only 5.1. This is not usually what you want.
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 confusion with both these properties is that the definition is not 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, as also does \p{Present_In: 3.1} and up.
\p{Print}This matches any character that is graphical or blank, except controls.
\p{SpacePerl}This is the 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 /i caseless matching, these match the same as \p{Cased}, whereas \p{gc=lt} matches \p{Cased_Letter).
\p{Unicode}This matches any of the 1_114_112 Unicode code points. \p{Any}.
\p{VertSpace}This is the same as \v: A character that changes the spacing vertically.
\p{Word}This is the same as \w, including over 100_000 characters beyond ASCII.
\p{XPosix...}There are several of these, which are the standard Posix classes extended to the full Unicode range. They are described in "POSIX Character Classes" in perlrecharclass.
\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{...}. The following summarizes the differences between these two:
\N{...} \p{Name=...}
can interpolate only with eval yes [1]
custom names yes no [2]
name aliases yes yes [3]
named sequences yes yes [4]
name value parsing exact Unicode loose [5]The ability to interpolate means you can do something like
qr/\p{na=latin capital letter $which}/and specify $which elsewhere.
You can create your own names for characters, and override official ones when using \N{...}. See "CUSTOM ALIASES" in charnames.
Some characters have multiple names (synonyms).
Some particular sequences of characters are given a single name, in addition to their individual ones.
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 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.
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 is independent of the main pattern, so 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 "}", as 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 is 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.
Your subpattern can be just about anything, but for it to have some utility, it should match when called with either or both of a) the full name of the property value with underscores (and/or spaces in the Block property) and some things uppercase; or b) the property value in all lowercase with spaces and underscores squeezed out. For example,
qr!\p{Blk=/Old I.*/}!
qr!\p{Blk=/oldi.*/}!would match the same things.
Another example that shows that within \p{...}, /x isn't needed to have spaces:
qr!\p{scx= /Hebrew|Greek/ }!To be safe, we should have anchored the above example, to prevent matches for something like Hebrew_Braille, but there aren't any script names like that, so far. A warning is issued if none of the legal values for a property are matched by your pattern. It's likely that a future release will raise a warning if your pattern ends up causing every possible code point to match.
Starting in 5.32, the Name, Name Aliases, and Named Sequences properties are allowed to be matched. They are considered to be a single combination property, just as has 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 are given in 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 bother trying to match one. The use of hyphens is particularly problematic; refer to the above link. 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 MappingNor is the @unicode_property@ form implemented.
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 sript
(?[ \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
(?: [.] $zero_through_255 ) {3}
)
\z
/x;You can define your own binary character properties by defining subroutines whose names begin with "In" or "Is". (The regex sets feature "(?[ ])" in perlre provides an alternative which allows more complex definitions.) The subroutines can be defined in any package. They override any Unicode properties expressed as the same names. The user-defined properties can be used in the regular expression \p{} and \P{} constructs; if you are using a user-defined property from a package other than the one you are in, you must specify its package in the \p{} or \P{} construct.
# assuming property IsForeign defined in Lang::
package main; # property package name required
if ($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 is 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 will 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 by "utf8::") 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 by "utf8::") 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 by "utf8::") 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 by "utf8::") 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.
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).
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
See