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charnames

Perl 5 version 20.0 documentation
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charnames

NAME

charnames - access to Unicode character names and named character sequences; also define character names

SYNOPSIS

  1.  use charnames ':full';
  2.  print "\N{GREEK SMALL LETTER SIGMA} is called sigma.\n";
  3.  print "\N{LATIN CAPITAL LETTER E WITH VERTICAL LINE BELOW}",
  4.        " is an officially named sequence of two Unicode characters\n";
  6.  use charnames ':loose';
  7.  print "\N{Greek small-letter  sigma}",
  8.         "can be used to ignore case, underscores, most blanks,"
  9.         "and when you aren't sure if the official name has hyphens\n";
  11.  use charnames ':short';
  12.  print "\N{greek:Sigma} is an upper-case sigma.\n";
  14.  use charnames qw(cyrillic greek);
  15.  print "\N{sigma} is Greek sigma, and \N{be} is Cyrillic b.\n";
  17.  use utf8;
  18.  use charnames ":full", ":alias" => {
  19.    e_ACUTE => "LATIN SMALL LETTER E WITH ACUTE",
  20.    mychar => 0xE8000,  # Private use area
  21.    "自転車に乗る人" => "BICYCLIST"
  22.  };
  23.  print "\N{e_ACUTE} is a small letter e with an acute.\n";
  24.  print "\N{mychar} allows me to name private use characters.\n";
  25.  print "And I can create synonyms in other languages,",
  26.        " such as \N{自転車に乗る人} for "BICYCLIST (U+1F6B4)\n";
  28.   use charnames ();
  29.   print charnames::viacode(0x1234); # prints "ETHIOPIC SYLLABLE SEE"
  30.   printf "%04X", charnames::vianame("GOTHIC LETTER AHSA"); # prints
  31.                                                                                                                     # "10330"
  32.   print charnames::vianame("LATIN CAPITAL LETTER A"); # prints 65 on
  33.                                                                                                           # ASCII platforms;
  34.                                                                                                           # 193 on EBCDIC
  35.   print charnames::string_vianame("LATIN CAPITAL LETTER A"); # prints "A"

DESCRIPTION

Pragma use charnames is used to gain access to the names of the Unicode characters and named character sequences, and to allow you to define your own character and character sequence names.

All forms of the pragma enable use of the following 3 functions:

Starting in Perl v5.16, any occurrence of \N{CHARNAME} sequences in a double-quotish string automatically loads this module with arguments :full and :short (described below) if it hasn't already been loaded with different arguments, in order to compile the named Unicode character into position in the string. Prior to v5.16, an explicit use charnames was required to enable this usage. (However, prior to v5.16, the form "use charnames ();" did not enable \N{CHARNAME}.)

Note that \N{U+...}, where the ... is a hexadecimal number, also inserts a character into a string. The character it inserts is the one whose Unicode code point (ordinal value) is equal to the number. For example, "\N{U+263a}" is the Unicode (white background, black foreground) smiley face equivalent to "\N{WHITE SMILING FACE}" . Also note, \N{...} can mean a regex quantifier instead of a character name, when the ... is a number (or comma separated pair of numbers (see QUANTIFIERS in perlreref), and is not related to this pragma.

The charnames pragma supports arguments :full , :loose , :short , script names and customized aliases.

If :full is present, for expansion of \N{CHARNAME}, the string CHARNAME is first looked up in the list of standard Unicode character names.

:loose is a variant of :full which allows CHARNAME to be less precisely specified. Details are in LOOSE MATCHES.

If :short is present, and CHARNAME has the form SCRIPT:CNAME, then CNAME is looked up as a letter in script SCRIPT, as described in the next paragraph. Or, if use charnames is used with script name arguments, then for \N{CHARNAME} the name CHARNAME is looked up as a letter in the given scripts (in the specified order). Customized aliases can override these, and are explained in CUSTOM ALIASES.

For lookup of CHARNAME inside a given script SCRIPTNAME, this pragma looks in the table of standard Unicode names for the names

  1.   SCRIPTNAME CAPITAL LETTER CHARNAME
  2.   SCRIPTNAME SMALL LETTER CHARNAME
  3.   SCRIPTNAME LETTER CHARNAME

If CHARNAME is all lowercase, then the CAPITAL variant is ignored, otherwise the SMALL variant is ignored, and both CHARNAME and SCRIPTNAME are converted to all uppercase for look-up. Other than that, both of them follow loose rules if :loose is also specified; strict otherwise.

Note that \N{...} is compile-time; it's a special form of string constant used inside double-quotish strings; this means that you cannot use variables inside the \N{...} . If you want similar run-time functionality, use charnames::string_vianame().

Note, starting in Perl 5.18, the name BELL refers to the Unicode character U+1F514, instead of the traditional U+0007. For the latter, use ALERT or BEL .

It is a syntax error to use \N{NAME} where NAME is unknown.

For \N{NAME} , it is a fatal error if use bytes is in effect and the input name is that of a character that won't fit into a byte (i.e., whose ordinal is above 255).

Otherwise, any string that includes a \N{charname} or \N{U+code point} will automatically have Unicode rules (see Byte and Character Semantics in perlunicode).

LOOSE MATCHES

By specifying :loose , Unicode's loose character name matching rules are selected instead of the strict exact match used otherwise. That means that CHARNAME doesn't have to be so precisely specified. Upper/lower case doesn't matter (except with scripts as mentioned above), nor do any underscores, and the only hyphens that matter are those at the beginning or end of a word in the name (with one exception: the hyphen in U+1180 HANGUL JUNGSEONG O-E does matter). Also, blanks not adjacent to hyphens don't matter. The official Unicode names are quite variable as to where they use hyphens versus spaces to separate word-like units, and this option allows you to not have to care as much. The reason non-medial hyphens matter is because of cases like U+0F60 TIBETAN LETTER -A versus U+0F68 TIBETAN LETTER A . The hyphen here is significant, as is the space before it, and so both must be included.

:loose slows down look-ups by a factor of 2 to 3 versus :full , but the trade-off may be worth it to you. Each individual look-up takes very little time, and the results are cached, so the speed difference would become a factor only in programs that do look-ups of many different spellings, and probably only when those look-ups are through vianame() and string_vianame() , since \N{...} look-ups are done at compile time.

ALIASES

Starting in Unicode 6.1 and Perl v5.16, Unicode defines many abbreviations and names that were formerly Perl extensions, and some additional ones that Perl did not previously accept. The list is getting too long to reproduce here, but you can get the complete list from the Unicode web site: http://www.unicode.org/Public/UNIDATA/NameAliases.txt.

Earlier versions of Perl accepted almost all the 6.1 names. These were most extensively documented in the v5.14 version of this pod: http://perldoc.perl.org/5.14.0/charnames.html#ALIASES.

CUSTOM ALIASES

You can add customized aliases to standard (:full ) Unicode naming conventions. The aliases override any standard definitions, so, if you're twisted enough, you can change "\N{LATIN CAPITAL LETTER A}" to mean "B" , etc.

Aliases must begin with a character that is alphabetic. After that, each may contain any combination of word (\w ) characters, SPACE (U+0020), HYPHEN-MINUS (U+002D), LEFT PARENTHESIS (U+0028), RIGHT PARENTHESIS (U+0029), and NO-BREAK SPACE (U+00A0). These last three should never have been allowed in names, and are retained for backwards compatibility only; they may be deprecated and removed in future releases of Perl, so don't use them for new names. (More precisely, the first character of a name you specify must be something that matches all of \p{ID_Start} , \p{Alphabetic} , and \p{Gc=Letter} . This makes sure it is what any reasonable person would view as an alphabetic character. And, the continuation characters that match \w must also match \p{ID_Continue} .) Starting with Perl v5.18, any Unicode characters meeting the above criteria may be used; prior to that only Latin1-range characters were acceptable.

An alias can map to either an official Unicode character name (not a loose matched name) or to a numeric code point (ordinal). The latter is useful for assigning names to code points in Unicode private use areas such as U+E800 through U+F8FF. A numeric code point must be a non-negative integer or a string beginning with "U+" or "0x" with the remainder considered to be a hexadecimal integer. A literal numeric constant must be unsigned; it will be interpreted as hex if it has a leading zero or contains non-decimal hex digits; otherwise it will be interpreted as decimal. If it begins with "U+" , it is interpreted as the Unicode code point; otherwise it is interpreted as native. (Only code points below 256 can differ between Unicode and native.) Thus U+41 is always the Latin letter "A"; but 0x41 can be "NO-BREAK SPACE" on EBCDIC platforms.

Aliases are added either by the use of anonymous hashes:

  1.     use charnames ":alias" => {
  2.         e_ACUTE => "LATIN SMALL LETTER E WITH ACUTE",
  3.         mychar1 => 0xE8000,
  4.         };
  5.     my $str = "\N{e_ACUTE}";

or by using a file containing aliases:

  1.     use charnames ":alias" => "pro";

This will try to read "unicore/pro_alias.pl" from the @INC path. This file should return a list in plain perl:

  1.     (
  2.     A_GRAVE         => "LATIN CAPITAL LETTER A WITH GRAVE",
  3.     A_CIRCUM        => "LATIN CAPITAL LETTER A WITH CIRCUMFLEX",
  4.     A_DIAERES       => "LATIN CAPITAL LETTER A WITH DIAERESIS",
  5.     A_TILDE         => "LATIN CAPITAL LETTER A WITH TILDE",
  6.     A_BREVE         => "LATIN CAPITAL LETTER A WITH BREVE",
  7.     A_RING          => "LATIN CAPITAL LETTER A WITH RING ABOVE",
  8.     A_MACRON        => "LATIN CAPITAL LETTER A WITH MACRON",
  9.     mychar2         => "U+E8001",
  10.     );

Both these methods insert ":full" automatically as the first argument (if no other argument is given), and you can give the ":full" explicitly as well, like

  1.     use charnames ":full", ":alias" => "pro";

":loose" has no effect with these. Input names must match exactly, using ":full" rules.

Also, both these methods currently allow only single characters to be named. To name a sequence of characters, use a custom translator (described below).

charnames::string_vianame(name)

This is a runtime equivalent to \N{...} . name can be any expression that evaluates to a name accepted by \N{...} under the :full option to charnames . In addition, any other options for the controlling "use charnames" in the same scope apply, like :loose or any script list, :short option, or custom aliases you may have defined.

The only differences are due to the fact that string_vianame is run-time and \N{} is compile time. You can't interpolate inside a \N{} , (so \N{$variable} doesn't work); and if the input name is unknown, string_vianame returns undef instead of it being a syntax error.

charnames::vianame(name)

This is similar to string_vianame . The main difference is that under most circumstances, vianame returns an ordinal code point, whereas string_vianame returns a string. For example,

  1.    printf "U+%04X", charnames::vianame("FOUR TEARDROP-SPOKED ASTERISK");

prints "U+2722".

This leads to the other two differences. Since a single code point is returned, the function can't handle named character sequences, as these are composed of multiple characters (it returns undef for these. And, the code point can be that of any character, even ones that aren't legal under the use bytes pragma,

See BUGS for the circumstances in which the behavior differs from that described above.

charnames::viacode(code)

Returns the full name of the character indicated by the numeric code. For example,

  1.     print charnames::viacode(0x2722);

prints "FOUR TEARDROP-SPOKED ASTERISK".

The name returned is the "best" (defined below) official name or alias for the code point, if available; otherwise your custom alias for it, if defined; otherwise undef. This means that your alias will only be returned for code points that don't have an official Unicode name (nor alias) such as private use code points.

If you define more than one name for the code point, it is indeterminate which one will be returned.

As mentioned, the function returns undef if no name is known for the code point. In Unicode the proper name for these is the empty string, which undef stringifies to. (If you ask for a code point past the legal Unicode maximum of U+10FFFF that you haven't assigned an alias to, you get undef plus a warning.)

The input number must be a non-negative integer, or a string beginning with "U+" or "0x" with the remainder considered to be a hexadecimal integer. A literal numeric constant must be unsigned; it will be interpreted as hex if it has a leading zero or contains non-decimal hex digits; otherwise it will be interpreted as decimal. If it begins with "U+" , it is interpreted as the Unicode code point; otherwise it is interpreted as native. (Only code points below 256 can differ between Unicode and native.) Thus U+41 is always the Latin letter "A"; but 0x41 can be "NO-BREAK SPACE" on EBCDIC platforms.

As mentioned above under ALIASES, Unicode 6.1 defines extra names (synonyms or aliases) for some code points, most of which were already available as Perl extensions. All these are accepted by \N{...} and the other functions in this module, but viacode has to choose which one name to return for a given input code point, so it returns the "best" name. To understand how this works, it is helpful to know more about the Unicode name properties. All code points actually have only a single name, which (starting in Unicode 2.0) can never change once a character has been assigned to the code point. But mistakes have been made in assigning names, for example sometimes a clerical error was made during the publishing of the Standard which caused words to be misspelled, and there was no way to correct those. The Name_Alias property was eventually created to handle these situations. If a name was wrong, a corrected synonym would be published for it, using Name_Alias. viacode will return that corrected synonym as the "best" name for a code point. (It is even possible, though it hasn't happened yet, that the correction itself will need to be corrected, and so another Name_Alias can be created for that code point; viacode will return the most recent correction.)

The Unicode name for each of the control characters (such as LINE FEED) is the empty string. However almost all had names assigned by other standards, such as the ASCII Standard, or were in common use. viacode returns these names as the "best" ones available. Unicode 6.1 has created Name_Aliases for each of them, including alternate names, like NEW LINE. viacode uses the original name, "LINE FEED" in preference to the alternate. Similarly the name returned for U+FEFF is "ZERO WIDTH NO-BREAK SPACE", not "BYTE ORDER MARK".

Until Unicode 6.1, the 4 control characters U+0080, U+0081, U+0084, and U+0099 did not have names nor aliases. To preserve backwards compatibility, any alias you define for these code points will be returned by this function, in preference to the official name.

Some code points also have abbreviated names, such as "LF" or "NL". viacode never returns these.

Because a name correction may be added in future Unicode releases, the name that viacode returns may change as a result. This is a rare event, but it does happen.

CUSTOM TRANSLATORS

The mechanism of translation of \N{...} escapes is general and not hardwired into charnames.pm. A module can install custom translations (inside the scope which uses the module) with the following magic incantation:

  1.     sub import {
  2.         shift;
  3.         $^H{charnames} = \&translator;
  4.     }

Here translator() is a subroutine which takes CHARNAME as an argument, and returns text to insert into the string instead of the \N{CHARNAME} escape.

This is the only way you can create a custom named sequence of code points.

Since the text to insert should be different in bytes mode and out of it, the function should check the current state of bytes -flag as in:

  1.     use bytes ();                      # for $bytes::hint_bits
  2.     sub translator {
  3.         if ($^H & $bytes::hint_bits) {
  4.             return bytes_translator(@_);
  5.         }
  6.         else {
  7.             return utf8_translator(@_);
  8.         }
  9.     }

See CUSTOM ALIASES above for restrictions on CHARNAME.

Of course, vianame , viacode , and string_vianame would need to be overridden as well.

BUGS

vianame() normally returns an ordinal code point, but when the input name is of the form U+... , it returns a chr instead. In this case, if use bytes is in effect and the character won't fit into a byte, it returns undef and raises a warning.

Since evaluation of the translation function (see CUSTOM TRANSLATORS) happens in the middle of compilation (of a string literal), the translation function should not do any evals or requires. This restriction should be lifted (but is low priority) in a future version of Perl.

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