charnames - define character names for CW\N{named} string literal escapes

  use charnames ':full';
  print "\N{GREEK SMALL LETTER SIGMA} is called sigma.\n";

  use charnames ':short';
  print "\N{greek:Sigma} is an upper-case sigma.\n";

  use charnames qw(cyrillic greek);
  print "\N{sigma} is Greek sigma, and \N{be} is Cyrillic b.\n";

  use charnames ":full", ":alias" => {
    e_ACUTE => "LATIN SMALL LETTER E WITH ACUTE",
  };
  print "\N{e_ACUTE} is a small letter e with an acute.\n";

  use charnames ();
  print charnames::viacode(0); # prints "ETHIOPIC SYLLABLE SEE"
  printf "%04X", charnames::vianame("GOTHIC LETTER AHSA"); # prints "10330"

Pragma CWuse charnames supports arguments CW:full, CW:short, script names and customized aliases. If CW:full is present, for expansion of CW\N{CHARNAME}, the string CWCHARNAME is first looked up in the list of standard Unicode character names. If CW:short is present, and CWCHARNAME has the form CWSCRIPT:CNAME, then CWCNAME is looked up as a letter in script CWSCRIPT. If pragma CWuse charnames is used with script name arguments, then for CW\N{CHARNAME} the name CWCHARNAME is looked up as a letter in the given scripts (in the specified order). Customized aliases are explained in CUSTOM ALIASES.

For lookup of CWCHARNAME inside a given script CWSCRIPTNAME this pragma looks for the names

  SCRIPTNAME CAPITAL LETTER CHARNAME
  SCRIPTNAME SMALL LETTER CHARNAME
  SCRIPTNAME LETTER CHARNAME

in the table of standard Unicode names. If CWCHARNAME is lowercase, then the CWCAPITAL variant is ignored, otherwise the CWSMALL variant is ignored.

Note that CW\N{...} is compile-time, it's a special form of string constant used inside double-quoted strings: in other words, you cannot use variables inside the CW\N{...}. If you want similar run-time functionality, use charnames::vianame().

For the C0 and C1 control characters (U+0000..U+001F, U+0080..U+009F) as of Unicode 3.1, there are no official Unicode names but you can use instead the ISO 6429 names (LINE FEED, ESCAPE, and so forth). In Unicode 3.2 (as of Perl 5.8) some naming changes take place ISO 6429 has been updated, see ALIASES. Also note that the U+UU80, U+0081, U+0084, and U+0099 do not have names even in ISO 6429.

Since the Unicode standard uses U+HHHH, so can you: \N{U+263a} is the Unicode smiley face, or \N{WHITE SMILING FACE}.

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

    use charnames ();           # for $charnames::hint_bits
    sub import {
        shift;
        $^H |= $charnames::hint_bits;
        $^H{charnames} = \&translator;
    }

Here translator() is a subroutine which takes CWCHARNAME as an argument, and returns text to insert into the string instead of the CW\N{CHARNAME} escape. Since the text to insert should be different in CWbytes mode and out of it, the function should check the current state of CWbytes-flag as in:

    use bytes ();                       # for $bytes::hint_bits
    sub translator {
        if ($^H & $bytes::hint_bits) {
            return bytes_translator(@_);
        }
        else {
            return utf8_translator(@_);
        }
    }

This version of charnames supports three mechanisms of adding local or customized aliases to standard Unicode naming conventions (:full)

    use charnames ":full", ":alias" => {
        e_ACUTE => "LATIN SMALL LETTER E WITH ACUTE",
        };
    my $str = "\N{e_ACUTE}";

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

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

    (
    A_GRAVE         => "LATIN CAPITAL LETTER A WITH GRAVE",
    A_CIRCUM        => "LATIN CAPITAL LETTER A WITH CIRCUMFLEX",
    A_DIAERES       => "LATIN CAPITAL LETTER A WITH DIAERESIS",
    A_TILDE         => "LATIN CAPITAL LETTER A WITH TILDE",
    A_BREVE         => "LATIN CAPITAL LETTER A WITH BREVE",
    A_RING          => "LATIN CAPITAL LETTER A WITH RING ABOVE",
    A_MACRON        => "LATIN CAPITAL LETTER A WITH MACRON",
    );

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

    works exactly the same as the alias pairs, only this time,
    ":full" is inserted automatically as first argument (if no
    other argument is given).

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

    print charnames::viacode(0);

prints FOUR TEARDROP-SPOKED ASTERISK.

Returns undef if no name is known for the code.

This works only for the standard names, and does not yet apply to custom translators.

Notice that the name returned for of U+FEFF is ZERO WIDTH NO-BREAK SPACE, not BYTE ORDER MARK.

Returns the code point indicated by the name. The example

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

prints 2722.

Returns undef if the name is unknown.

This works only for the standard names, and does not yet apply to custom translators.

A few aliases have been defined for convenience: instead of having to use the official names

    LINE FEED (LF)
    FORM FEED (FF)
    CARRIAGE RETURN (CR)
    NEXT LINE (NEL)

(yes, with parentheses) one can use

    LINE FEED
    FORM FEED
    CARRIAGE RETURN
    NEXT LINE
    LF
    FF
    CR
    NEL

One can also use

    BYTE ORDER MARK
    BOM

and

    ZWNJ
    ZWJ

for ZERO WIDTH NON-JOINER and ZERO WIDTH JOINER.

For backward compatibility one can use the old names for certain C0 and C1 controls

    old                         new

    HORIZONTAL TABULATION       CHARACTER TABULATION
    VERTICAL TABULATION         LINE TABULATION
    FILE SEPARATOR              INFORMATION SEPARATOR FOUR
    GROUP SEPARATOR             INFORMATION SEPARATOR THREE
    RECORD SEPARATOR            INFORMATION SEPARATOR TWO
    UNIT SEPARATOR              INFORMATION SEPARATOR ONE
    PARTIAL LINE DOWN           PARTIAL LINE FORWARD
    PARTIAL LINE UP             PARTIAL LINE BACKWARD

but the old names in addition to giving the character will also give a warning about being deprecated.

If you ask by name for a character that does not exist, a warning is given and the Unicode replacement character \x{FFFD} is returned.

If you ask by code for a character that does not exist, no warning is given and CWundef is returned. (Though if you ask for a code point past U+10FFFF you do get a warning.)

Since evaluation of the translation function happens in a middle of compilation (of a string literal), the translation function should not do any CWevals or CWrequires. This restriction should be lifted in a future version of Perl.