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Unicode support in Perl

perlunicode - Unicode support in Perl


perlunicode - Unicode support in Perl


Important Caveats

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.

Input and Output Disciplines
A filehandle can be marked as containing perl's internal Unicode encoding (UTF-8 or UTF-EBCDIC) by opening it with the ``:utf8'' layer. Other encodings can be converted to perl's encoding on input, or from perl's encoding on output by use of the ``:encoding(...)'' layer. See open.

To mark the Perl source itself as being in a particular encoding, see encoding.

Regular Expressions
The regular expression compiler produces polymorphic opcodes. That is, the pattern adapts to the data and automatically switch to the Unicode character scheme when presented with Unicode data, or a traditional byte scheme when presented with byte data.

use utf8 still needed to enable UTF-8/UTF-EBCDIC in scripts
As a compatibility measure, this pragma must be explicitly used to enable recognition of UTF-8 in the Perl scripts themselves on ASCII based machines, or to recognize UTF-EBCDIC on EBCDIC based machines. NOTE: this should be the only place where an explicit use utf8 is needed.

You can also use the encoding pragma to change the default encoding of the data in your script; see encoding.

Byte and Character semantics

Beginning with version 5.6, Perl uses logically wide characters to represent strings internally.

In future, Perl-level operations can be expected to work with characters rather than bytes, in general.

However, as strictly an interim compatibility measure, Perl aims to provide a safe migration path from byte semantics to character semantics for programs. For operations where Perl can unambiguously decide that the input data is characters, Perl now switches to character semantics. For operations where this determination cannot be made without additional information from the user, Perl decides in favor of compatibility, and chooses to use byte semantics.

This behavior preserves compatibility with earlier versions of Perl, which allowed byte semantics in Perl operations, but only as long as none of the program's inputs are marked as being as source of Unicode character data. Such data may come from filehandles, from calls to external programs, from information provided by the system (such as %ENV), or from literals and constants in the source text.

On Windows platforms, if the -C command line switch is used, (or the ${^WIDE_SYSTEM_CALLS} global flag is set to 1), all system calls will use the corresponding wide character APIs. Note that this is currently only implemented on Windows since other platforms lack an API standard on this area.

Regardless of the above, the bytes pragma can always be used to force byte semantics in a particular lexical scope. See bytes.

The utf8 pragma is primarily a compatibility device that enables recognition of UTF-(8|EBCDIC) in literals encountered by the parser. Note that this pragma is only required until a future version of Perl in which character semantics will become the default. This pragma may then become a no-op. See utf8.

Unless mentioned otherwise, Perl operators will use character semantics when they are dealing with Unicode data, and byte semantics otherwise. Thus, character semantics for these operations apply transparently; if the input data came from a Unicode source (for example, by adding a character encoding discipline to the filehandle whence it came, or a literal Unicode string constant in the program), character semantics apply; otherwise, byte semantics are in effect. To force byte semantics on Unicode data, the bytes pragma should be used.

Notice that if you concatenate strings with byte semantics and strings with Unicode character data, the bytes will by default be upgraded as if they were ISO 8859-1 (Latin-1) (or if in EBCDIC, after a translation to ISO 8859-1). This is done without regard to the system's native 8-bit encoding, so to change this for systems with non-Latin-1 (or non-EBCDIC) native encodings, use the encoding pragma, see encoding.

Under character semantics, many operations that formerly operated on bytes change to operating on characters. A character in Perl is logically just a number ranging from 0 to 2**31 or so. Larger characters may encode to longer sequences of bytes internally, but this is just an internal detail which is hidden at the Perl level. See perluniintro for more on this.

Effects of character semantics

Character semantics have the following effects:

  • Strings and patterns may contain characters that have an ordinal value larger than 255.

    If you use a Unicode editor to edit your program, Unicode characters may occur directly within the literal strings in one of the various Unicode encodings (UTF-8, UTF-EBCDIC, UCS-2, etc.), but are recognized as such (and converted to Perl's internal representation) only if the appropriate encoding is specified.

    You can also get Unicode characters into a string by using the \x{...} notation, putting the Unicode code for the desired character, in hexadecimal, into the curlies. For instance, a smiley face is \x{263A}. This works only for characters with a code 0x100 and above.

    Additionally, if you use charnames ':full'; you can use the \N{...} notation, putting the official Unicode character name within the curlies. For example, \N{WHITE SMILING FACE}. This works for all characters that have names.

  • If an appropriate encoding is specified, identifiers within the Perl script may contain Unicode alphanumeric characters, including ideographs. (You are currently on your own when it comes to using the canonical forms of characters--Perl doesn't (yet) attempt to canonicalize variable names for you.)

  • Regular expressions match characters instead of bytes. For instance, ``.'' matches a character instead of a byte. (However, the \C pattern is provided to force a match a single byte (``char'' in C, hence \C).)

  • Character classes in regular expressions match characters instead of bytes, and match against the character properties specified in the Unicode properties database. So \w can be used to match an ideograph, for instance.

  • Named Unicode properties, scripts, and block ranges may be used like character classes via the new \p{} (matches property) and \P{} (doesn't match property) constructs. For instance, \p{Lu} matches any character with the Unicode ``Lu'' (Letter, uppercase) property, while \p{M} matches any character with a ``M'' (mark -- accents and such) property. Single letter properties may omit the brackets, so that can be written \pM also. Many predefined properties are available, such as \p{Mirrored} and \p{Tibetan}.

    The official Unicode script and block names have spaces and dashes as separators, but for convenience you can have dashes, spaces, and underbars at every word division, and you need not care about correct casing. It is recommended, however, that for consistency you use the following naming: the official Unicode script, block, or property name (see below for the additional rules that apply to block names), with whitespace and dashes removed, and the words ``uppercase-first-lowercase-rest''. That is, ``Latin-1 Supplement'' becomes ``Latin1Supplement''.

    You can also negate both \p{} and \P{} by introducing a caret (^) between the first curly and the property name: \p{^Tamil} is equal to \P{Tamil}.

    Here are the basic Unicode General Category properties, followed by their long form (you can use either, e.g. \p{Lu} and \p{LowercaseLetter} are identical).

        Short       Long
        L           Letter
        Lu          UppercaseLetter
        Ll          LowercaseLetter
        Lt          TitlecaseLetter
        Lm          ModifierLetter
        Lo          OtherLetter
        M           Mark
        Mn          NonspacingMark
        Mc          SpacingMark
        Me          EnclosingMark
        N           Number
        Nd          DecimalNumber
        Nl          LetterNumber
        No          OtherNumber
        P           Punctuation
        Pc          ConnectorPunctuation
        Pd          DashPunctuation
        Ps          OpenPunctuation
        Pe          ClosePunctuation
        Pi          InitialPunctuation
                    (may behave like Ps or Pe depending on usage)
        Pf          FinalPunctuation
                    (may behave like Ps or Pe depending on usage)
        Po          OtherPunctuation
        S           Symbol
        Sm          MathSymbol
        Sc          CurrencySymbol
        Sk          ModifierSymbol
        So          OtherSymbol
        Z           Separator
        Zs          SpaceSeparator
        Zl          LineSeparator
        Zp          ParagraphSeparator
        C           Other
        Cc          Control
        Cf          Format
        Cs          Surrogate   (not usable)
        Co          PrivateUse
        Cn          Unassigned

    The single-letter properties match all characters in any of the two-letter sub-properties starting with the same letter. There's also L& which is an alias for Ll, Lu, and Lt.

    Because Perl hides the need for the user to understand the internal representation of Unicode characters, it has no need to support the somewhat messy concept of surrogates. Therefore, the Cs property is not supported.

    Because scripts differ in their directionality (for example Hebrew is written right to left), Unicode supplies these properties:

        Property    Meaning
        BidiL       Left-to-Right
        BidiLRE     Left-to-Right Embedding
        BidiLRO     Left-to-Right Override
        BidiR       Right-to-Left
        BidiAL      Right-to-Left Arabic
        BidiRLE     Right-to-Left Embedding
        BidiRLO     Right-to-Left Override
        BidiPDF     Pop Directional Format
        BidiEN      European Number
        BidiES      European Number Separator
        BidiET      European Number Terminator
        BidiAN      Arabic Number
        BidiCS      Common Number Separator
        BidiNSM     Non-Spacing Mark
        BidiBN      Boundary Neutral
        BidiB       Paragraph Separator
        BidiS       Segment Separator
        BidiWS      Whitespace
        BidiON      Other Neutrals

    For example, \p{BidiR} matches all characters that are normally written right to left.


The scripts available via \p{...} and \P{...}, for example \p{Latin} or \p{Cyrillic>, are as follows:









































There are also extended property classes that supplement the basic properties, defined by the PropList Unicode database:

















and further derived properties:

    Alphabetic      Lu + Ll + Lt + Lm + Lo + OtherAlphabetic

    Lowercase       Ll + OtherLowercase

    Uppercase       Lu + OtherUppercase

    Math            Sm + OtherMath

    ID_Start        Lu + Ll + Lt + Lm + Lo + Nl

    ID_Continue     ID_Start + Mn + Mc + Nd + Pc

    Any             Any character

    Assigned        Any non-Cn character (i.e. synonym for C<\P{Cn}>)

    Unassigned      Synonym for C<\p{Cn}>

    Common          Any character (or unassigned code point)

                    not explicitly assigned to a script

For backward compatability, all properties mentioned so far may have Is prepended to their name (e.g. \P{IsLu} is equal to \P{Lu}).


In addition to scripts, Unicode also defines blocks of characters. The difference between scripts and blocks is that the scripts concept is closer to natural languages, while the blocks concept is more an artificial grouping based on groups of mostly 256 Unicode characters. For example, the Latin script contains letters from many blocks. On the other hand, the Latin script does not contain all the characters from those blocks. It does not, for example, contain digits because digits are shared across many scripts. Digits and other similar groups, like punctuation, are in a category called Common.

For more about scripts, see the UTR #24:

For more about blocks, see:

Blocks names are given with the In prefix. For example, the Katakana block is referenced via \p{InKatakana}. The In prefix may be omitted if there is no nameing conflict with a script or any other property, but it is recommended that In always be used to avoid confusion.

These block names are supported:
































































































  • The special pattern \X match matches any extended Unicode sequence (a ``combining character sequence'' in Standardese), where the first character is a base character and subsequent characters are mark characters that apply to the base character. It is equivalent to (?:\PM\pM*).

  • The tr/// operator translates characters instead of bytes. Note that the tr///CU functionality has been removed, as the interface was a mistake. For similar functionality see pack('U0', ...) and pack('C0', ...).

  • Case translation operators use the Unicode case translation tables when provided character input. Note that uc() (also known as \U in doublequoted strings) translates to uppercase, while ucfirst (also known as \u in doublequoted strings) translates to titlecase (for languages that make the distinction). Naturally the corresponding backslash sequences have the same semantics.

  • Most operators that deal with positions or lengths in the string will automatically switch to using character positions, including chop(), substr(), pos(), index(), rindex(), sprintf(), write(), and length(). Operators that specifically don't switch include vec(), pack(), and unpack(). Operators that really don't care include chomp(), as well as any other operator that treats a string as a bucket of bits, such as sort(), and the operators dealing with filenames.

  • The pack()/unpack() letters ``c'' and ``C'' do not change, since they're often used for byte-oriented formats. (Again, think ``char'' in the C language.) However, there is a new ``U'' specifier that will convert between Unicode characters and integers.

  • The chr() and ord() functions work on characters. This is like pack("U") and unpack("U"), not like pack("C") and unpack("C"). In fact, the latter are how you now emulate byte-oriented chr() and ord() for Unicode strings. (Note that this reveals the internal encoding of Unicode strings, which is not something one normally needs to care about at all.)

  • The bit string operators & | ^ ~ can operate on character data. However, for backward compatibility reasons (bit string operations when the characters all are less than 256 in ordinal value) one should not mix ~ (the bit complement) and characters both less than 256 and equal or greater than 256. Most importantly, the DeMorgan's laws (~($x|$y) eq ~$x&~$y, ~($x&$y) eq ~$x|~$y) won't hold. Another way to look at this is that the complement cannot return both the 8-bit (byte) wide bit complement and the full character wide bit complement.

  • lc(), uc(), lcfirst(), and ucfirst() work for the following cases:
    • the case mapping is from a single Unicode character to another single Unicode character

    • the case mapping is from a single Unicode character to more than one Unicode character

    What doesn't yet work are the following cases:

    • the ``final sigma'' (Greek)

    • anything to with locales (Lithuanian, Turkish, Azeri)

    See the Unicode Technical Report #21, Case Mappings, for more details.

  • And finally, scalar reverse() reverses by character rather than by byte.

Character encodings for input and output

See Encode.


Whether an arbitrary piece of data will be treated as ``characters'' or ``bytes'' by internal operations cannot be divined at the current time.

Use of locales with Unicode data may lead to odd results. Currently there is some attempt to apply 8-bit locale info to characters in the range 0..255, but this is demonstrably incorrect for locales that use characters above that range when mapped into Unicode. It will also tend to run slower. Avoidance of locales is strongly encouraged.


The following list of Unicode regular expression support describes feature by feature the Unicode support implemented in Perl as of Perl 5.8.0. The ``Level N'' and the section numbers refer to the Unicode Technical Report 18, ``Unicode Regular Expression Guidelines''.

  • Level 1 - Basic Unicode Support
            2.1 Hex Notation                        - done          [1]
                Named Notation                      - done          [2]
            2.2 Categories                          - done          [3][4]
            2.3 Subtraction                         - MISSING       [5][6]
            2.4 Simple Word Boundaries              - done          [7]
            2.5 Simple Loose Matches                - done          [8]
            2.6 End of Line                         - MISSING       [9][10]
            [ 1] \x{...}
            [ 2] \N{...}
            [ 3] . \p{...} \P{...}
            [ 4] now scripts (see UTR#24 Script Names) in addition to blocks
            [ 5] have negation
            [ 6] can use look-ahead to emulate subtraction (*)
            [ 7] include Letters in word characters
            [ 8] note that perl does Full casefolding in matching, not Simple:
                 for example U+1F88 is equivalent with U+1F000 U+03B9,
                 not with 1F80.  This difference matters for certain Greek
                 capital letters with certain modifiers: the Full casefolding
                 decomposes the letter, while the Simple casefolding would map
                 it to a single character.
            [ 9] see UTR#13 Unicode Newline Guidelines
            [10] should do ^ and $ also on \x{85}, \x{2028} and \x{2029})
                 (should also affect <>, $., and script line numbers)
                 (the \x{85}, \x{2028} and \x{2029} do match \s)

    (*) You can mimic class subtraction using lookahead. For example, what TR18 might write as


    in Perl can be written as:


    But in this particular example, you probably really want


    which will match assigned characters known to be part of the Greek script.

  • Level 2 - Extended Unicode Support
            3.1 Surrogates                          - MISSING
            3.2 Canonical Equivalents               - MISSING       [11][12]
            3.3 Locale-Independent Graphemes        - MISSING       [13]
            3.4 Locale-Independent Words            - MISSING       [14]
            3.5 Locale-Independent Loose Matches    - MISSING       [15]
            [11] see UTR#15 Unicode Normalization
            [12] have Unicode::Normalize but not integrated to regexes
            [13] have \X but at this level . should equal that
            [14] need three classes, not just \w and \W
            [15] see UTR#21 Case Mappings

  • Level 3 - Locale-Sensitive Support
            4.1 Locale-Dependent Categories         - MISSING
            4.2 Locale-Dependent Graphemes          - MISSING       [16][17]
            4.3 Locale-Dependent Words              - MISSING
            4.4 Locale-Dependent Loose Matches      - MISSING
            4.5 Locale-Dependent Ranges             - MISSING
            [16] see UTR#10 Unicode Collation Algorithms
            [17] have Unicode::Collate but not integrated to regexes

Unicode Encodings

Unicode characters are assigned to code points which are abstract numbers. To use these numbers various encodings are needed.


UTF-8 is a variable-length (1 to 6 bytes, current character allocations require 4 bytes), byteorder independent encoding. For ASCII, UTF-8 is transparent (and we really do mean 7-bit ASCII, not another 8-bit encoding).

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       ******* ill-formed *******

   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..BF

Note the A0..BF in U+0800..U+0FFF, the 80..9F in U+D000...U+D7FF, the 90..BF in U+10000..U+3FFFF, and the 80...8F in U+100000..U+10FFFF. Or, another way to look at it, as bits:

 Code Points                    1st Byte   2nd Byte  3rd Byte  4th Byte

                    0aaaaaaa     0aaaaaaa

            00000bbbbbaaaaaa     110bbbbb  10aaaaaa

            ccccbbbbbbaaaaaa     1110cccc  10bbbbbb  10aaaaaa

  00000dddccccccbbbbbbaaaaaa     11110ddd  10cccccc  10bbbbbb  10aaaaaa

As you can see, the continuation bytes all begin with 10, and the leading bits of the start byte tell how many bytes the are in the encoded character.


Like UTF-8, but EBCDIC-safe, as UTF-8 is ASCII-safe.

UTF-16, UTF-16BE, UTF16-LE, Surrogates, and BOMs (Byte Order Marks)

(The followings items are mostly for reference, Perl doesn't use them internally.)

UTF-16 is a 2 or 4 byte encoding. The Unicode code points 0x0000..0xFFFF are stored in two 16-bit units, and the code points 0x010000..0x10FFFF in two 16-bit units. The latter case is using 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 0x01000..0x10FFFF range of Unicode code points in pairs of 16-bit units. The high surrogates are the range 0xD800..0xDBFF, and the low surrogates are the range 0xDC00..0xDFFFF. The surrogate encoding is

        $hi = ($uni - 0x10000) / 0x400 + 0xD800;

        $lo = ($uni - 0x10000) % 0x400 + 0xDC00;

and the decoding is

        $uni = 0x10000 + ($hi - 0xD8000) * 0x400 + ($lo - 0xDC00);

If you try to generate surrogates (for example by using chr()), you will get a warning if warnings are turned on (-w or use warnings;) because those code points are not valid for a Unicode character.

Because of the 16-bitness, UTF-16 is byteorder dependent. UTF-16 itself can be used for in-memory computations, but if storage or transfer is required, either UTF-16BE (Big Endian) or UTF-16LE (Little Endian) must be chosen.

This introduces another problem: what if you just know that your data is UTF-16, but you don't know which endianness? Byte Order Marks (BOMs) are a solution to this. A special character has been reserved in Unicode to function as a byte order marker: the character with the code point 0xFEFF is the BOM.

The trick is that if you read a BOM, you will know the byte order, since if it was written on a big endian platform, you will read the bytes 0xFE 0xFF, but if it was written on a little endian platform, you will read the bytes 0xFF 0xFE. (And if the originating platform was writing in UTF-8, you will read the bytes 0xEF 0xBB 0xBF.)

The way this trick works is that the character with the code point 0xFFFE is guaranteed not to be a valid Unicode character, so the sequence of bytes 0xFF 0xFE is unambiguously ``BOM, represented in little-endian format'' and cannot be ``0xFFFE, represented in big-endian format''.

UTF-32, UTF-32BE, UTF32-LE

The UTF-32 family is pretty much like the UTF-16 family, expect that the units are 32-bit, and therefore the surrogate scheme is not needed. The BOM signatures will be 0x00 0x00 0xFE 0xFF for BE and 0xFF 0xFE 0x00 0x00 for LE.

UCS-2, UCS-4

Encodings defined by the ISO 10646 standard. UCS-2 is a 16-bit encoding, UCS-4 is a 32-bit encoding. Unlike UTF-16, UCS-2 is not extensible beyond 0xFFFF, because it does not use surrogates.


A seven-bit safe (non-eight-bit) encoding, useful if the transport/storage is not eight-bit safe. Defined by RFC 2152.

Security Implications of Malformed UTF-8

Unfortunately, the specification of UTF-8 leaves some room for interpretation of how many bytes of encoded output one should generate from one input Unicode character. Strictly speaking, one is supposed to always generate the shortest possible sequence of UTF-8 bytes, because otherwise there is potential for input buffer overflow at the receiving end of a UTF-8 connection. Perl always generates the shortest length UTF-8, and with warnings on (-w or use warnings;) Perl will warn about non-shortest length UTF-8 (and other malformations, too, such as the surrogates, which are not real Unicode code points.)

Unicode in Perl on EBCDIC

The way Unicode is handled on EBCDIC platforms is still rather experimental. On such a platform, references to UTF-8 encoding in this document and elsewhere should be read as meaning UTF-EBCDIC as specified in Unicode Technical Report 16 unless ASCII vs EBCDIC issues are specifically discussed. There is no utfebcdic pragma or ``:utfebcdic'' layer, rather, ``utf8'' and ``:utf8'' are re-used to mean the platform's ``natural'' 8-bit encoding of Unicode. See perlebcdic for more discussion of the issues.

Using Unicode in XS

If you want to handle Perl Unicode in XS extensions, you may find the following C APIs useful (see perlapi for details):

  • DO_UTF8(sv) returns true if the UTF8 flag is on and the bytes pragma is not in effect. SvUTF8(sv) returns true is the UTF8 flag is on, the bytes pragma is ignored. The UTF8 flag being on does not mean that there are any characters of code points greater than 255 (or 127) in the scalar, or that there even are any characters in the scalar. What the UTF8 flag means is that the sequence of octets in the representation of the scalar is the sequence of UTF-8 encoded code points of the characters of a string. The UTF8 flag being off means that each octet in this representation encodes a single character with codepoint 0..255 within the string. Perl's Unicode model is not to use UTF-8 until it's really necessary.

  • uvuni_to_utf8(buf, chr) writes a Unicode character code point into a buffer encoding the code point as UTF-8, and returns a pointer pointing after the UTF-8 bytes.

  • utf8_to_uvuni(buf, lenp) reads UTF-8 encoded bytes from a buffer and returns the Unicode character code point (and optionally the length of the UTF-8 byte sequence).

  • utf8_length(start, end) returns the length of the UTF-8 encoded buffer in characters. sv_len_utf8(sv) returns the length of the UTF-8 encoded scalar.

  • sv_utf8_upgrade(sv) converts the string of the scalar to its UTF-8 encoded form. sv_utf8_downgrade(sv) does the opposite (if possible). sv_utf8_encode(sv) is like sv_utf8_upgrade but the UTF8 flag does not get turned on. sv_utf8_decode() does the opposite of sv_utf8_encode().

  • is_utf8_char(s) returns true if the pointer points to a valid UTF-8 character.

  • is_utf8_string(buf, len) returns true if the len bytes of the buffer are valid UTF-8.

  • UTF8SKIP(buf) will return the number of bytes in the UTF-8 encoded character in the buffer. UNISKIP(chr) will return the number of bytes required to UTF-8-encode the Unicode character code point. UTF8SKIP() is useful for example for iterating over the characters of a UTF-8 encoded buffer; UNISKIP() is useful for example in computing the size required for a UTF-8 encoded buffer.

  • utf8_distance(a, b) will tell the distance in characters between the two pointers pointing to the same UTF-8 encoded buffer.

  • utf8_hop(s, off) will return a pointer to an UTF-8 encoded buffer that is off (positive or negative) Unicode characters displaced from the UTF-8 buffer s. Be careful not to overstep the buffer: utf8_hop() will merrily run off the end or the beginning if told to do so.

  • pv_uni_display(dsv, spv, len, pvlim, flags) and sv_uni_display(dsv, ssv, pvlim, flags) are useful for debug output of Unicode strings and scalars. By default they are useful only for debug: they display all characters as hexadecimal code points, but with the flags UNI_DISPLAY_ISPRINT and UNI_DISPLAY_BACKSLASH you can make the output more readable.

  • ibcmp_utf8(s1, pe1, u1, l1, u1, s2, pe2, l2, u2) can be used to compare two strings case-insensitively in Unicode. (For case-sensitive comparisons you can just use memEQ() and memNE() as usual.)

For more information, see perlapi, and utf8.c and utf8.h in the Perl source code distribution.


perluniintro, encoding, Encode, open, utf8, bytes, perlretut, perlvar/``${^WIDE_SYSTEM_CALLS}''