PERLUNICODE(1) Perl Programmers Reference Guide PERLUNICODE(1)
NAME
perlunicode - Unicode support in Perl
DESCRIPTION
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.
People who want to learn to use Unicode in Perl, should probably read the Perl Unicode tutorial, perlunitut
and perluniintro, before reading this reference document.
Also, the use of Unicode may present security issues that aren't obvious. Read Unicode Security
Considerations <http://www.unicode.org/reports/tr36>.
Safest if you "use feature 'unicode_strings'"
In order to preserve backward compatibility, Perl does not turn on full internal Unicode support unless
the pragma "use feature 'unicode_strings'" is specified. (This is automatically selected if you use "use
5.012" or higher.) Failure to do this can trigger unexpected surprises. See "The "Unicode Bug"" below.
This pragma doesn't affect I/O, and there are still several places where Unicode isn't fully supported,
such as in filenames.
Input and Output Layers
Perl knows when a filehandle uses Perl's internal Unicode encodings (UTF-8, or UTF-EBCDIC if in EBCDIC) if
the filehandle is opened with the ":encoding(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 indicate that Perl source itself is in UTF-8, use "use utf8;".
"use utf8" still needed to enable UTF-8/UTF-EBCDIC in scripts
As a compatibility measure, the "use utf8" pragma must be explicitly included to enable recognition of
UTF-8 in the Perl scripts themselves (in string or regular expression literals, or in identifier names) on
ASCII-based machines or to recognize UTF-EBCDIC on EBCDIC-based machines. These are the only times when
an explicit "use utf8" is needed. See utf8.
BOM-marked scripts and UTF-16 scripts autodetected
If a Perl script begins marked with the Unicode BOM (UTF-16LE, UTF16-BE, or UTF-8), or if the script looks
like non-BOM-marked UTF-16 of either endianness, Perl will correctly read in the script as Unicode.
(BOMless UTF-8 cannot be effectively recognized or differentiated from ISO 8859-1 or other eight-bit
encodings.)
"use encoding" needed to upgrade non-Latin-1 byte strings
By default, there is a fundamental asymmetry in Perl's Unicode model: implicit upgrading from byte strings
to Unicode strings assumes that they were encoded in ISO 8859-1 (Latin-1), but Unicode strings are
downgraded with UTF-8 encoding. This happens because the first 256 codepoints in Unicode happens to agree
with Latin-1.
See "Byte and Character Semantics" for more details.
Byte and Character Semantics
Beginning with version 5.6, Perl uses logically-wide characters to represent strings internally.
Starting in Perl 5.14, Perl-level operations work with characters rather than bytes within the scope of a "use
feature 'unicode_strings'" (or equivalently "use 5.012" or higher). (This is not true if bytes have been
explicitly requested by "use bytes", nor necessarily true for interactions with the platform's operating
system.)
seamless, as the EBCDIC code pages that Perl handles are equivalent to Unicode's first 256 code points. (The
exception is that EBCDIC regular expression case-insensitive matching rules are not as as robust as
Unicode's.) But on ASCII platforms, Perl uses US-ASCII (or Basic Latin in Unicode terminology) byte
semantics, meaning that characters whose ordinal numbers are in the range 128 - 255 are undefined except for
their ordinal numbers. This means that none have case (upper and lower), nor are any a member of character
classes, like "[:alpha:]" or "\w". (But all do belong to the "\W" class or the Perl regular expression
extension "[:^alpha:]".)
This behavior preserves compatibility with earlier versions of Perl, which allowed byte semantics in Perl
operations only if none of the program's inputs were marked as being a 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.
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 while Perl defaults to byte semantics; when
character semantics become the default, this pragma may become a no-op. See utf8.
If strings operating under byte semantics and strings with Unicode character data are concatenated, the new
string will have character semantics. This can cause surprises: See "BUGS", below. You can choose to be
warned when this happens. See encoding::warnings.
Under character semantics, many operations that formerly operated on bytes now operate on characters. A
character in Perl is logically just a number ranging from 0 to 2**31 or so. Larger characters may encode into
longer sequences of bytes internally, but this internal detail is mostly hidden for Perl code. See
perluniintro for more.
Effects of Character Semantics
Character semantics have the following effects:
· Strings--including hash keys--and regular expression 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 UTF-8 encoding, or UTF-16. (The former requires a BOM or "use utf8", the latter requires a
BOM.)
Unicode characters can also be added to a string by using the "\N{U+...}" notation. The Unicode code for
the desired character, in hexadecimal, should be placed in the braces, after the "U". For instance, a
smiley face is "\N{U+263A}".
Alternatively, you can use the "\x{...}" notation for characters 0x100 and above. For characters below
0x100 you may get byte semantics instead of character semantics; see "The "Unicode Bug"". On EBCDIC
machines there is the additional problem that the value for such characters gives the EBCDIC character
rather than the Unicode one, thus it is more portable to use "\N{U+...}" instead.
Additionally, you can use the "\N{...}" notation and put the official Unicode character name within the
braces, such as "\N{WHITE SMILING FACE}". This automatically loads the charnames module with the ":full"
and ":short" options. If you prefer different options for this module, you can instead, before the
"\N{...}", explicitly load it with your desired options; for example,
use charnames ':loose';
· If an appropriate encoding is specified, identifiers within the Perl script may contain Unicode
alphanumeric characters, including ideographs. Perl does not currently attempt to canonicalize variable
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.
· The special pattern "\X" matches a logical character, an "extended grapheme cluster" in Standardese. In
Unicode what appears to the user to be a single character, for example an accented "G", may in fact be
composed of a sequence of characters, in this case a "G" followed by an accent character. "\X" will match
the entire sequence.
· The "tr///" operator translates characters instead of bytes. Note that the "tr///CU" functionality has
been removed. For similar functionality see pack('U0', ...) and pack('C0', ...).
· Case translation operators use the Unicode case translation tables when character input is provided. 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).
· Most operators that deal with positions or lengths in a string will automatically switch to using
character positions, including "chop()", "chomp()", "substr()", "pos()", "index()", "rindex()",
"sprintf()", "write()", and "length()". An operator that specifically does not switch is "vec()".
Operators that really don't care include operators that treat strings as a bucket of bits such as
"sort()", and operators dealing with filenames.
· The "pack()"/"unpack()" letter "C" does not change, since it is often used for byte-oriented formats.
Again, think "char" in the C language.
There is a new "U" specifier that converts between Unicode characters and code points. There is also a "W"
specifier that is the equivalent of "chr"/"ord" and properly handles character values even if they are
above 255.
· The "chr()" and "ord()" functions work on characters, similar to "pack("W")" and "unpack("W")", not
"pack("C")" and "unpack("C")". "pack("C")" and "unpack("C")" are methods for emulating byte-oriented
"chr()" and "ord()" on Unicode strings. While these methods reveal the internal encoding of Unicode
strings, that is not something one normally needs to care about at all.
· The bit string operators, "& | ^ ~", can operate on character data. However, for backward compatibility,
such as when using bit string operations when characters are all less than 256 in ordinal value, one
should not use "~" (the bit complement) with characters of both values less than 256 and values greater
than 256. Most importantly, DeMorgan's laws ("~($x|$y) eq ~$x&~$y" and "~($x&$y) eq ~$x|~$y") will not
hold. The reason for this mathematical faux pas is that the complement cannot return both the 8-bit
(byte-wide) bit complement and the full character-wide bit complement.
· 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.)
· And finally, "scalar reverse()" reverses by character rather than by byte.
Unicode Character Properties
(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{}"
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 same short form 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 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 few places where stricter matching is used is in the middle of numbers, 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"
matching 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.)
The result is undefined if you try to match a non-Unicode code point (that is, one above 0x10FFFF) against a
Unicode property. Currently, a warning is raised, and the match will fail. In some cases, this is
counterintuitive, as both these fail:
chr(0x110000) =~ \p{ASCII_Hex_Digit=True} # Fails.
chr(0x110000) =~ \p{ASCII_Hex_Digit=False} # Fails!
General_Category
Every Unicode character is assigned a general category, which is the "most usual categorization of a
character" (from <http://www.unicode.org/reports/tr44>).
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 Unassigned
Single-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".
Bidirectional Character Types
Because scripts differ in their directionality (Hebrew and Arabic are written right to left, for example)
Unicode supplies these properties in the Bidi_Class class:
Property Meaning
CS Common Separator
NSM Non-Spacing Mark
BN Boundary Neutral
B Paragraph Separator
S Segment Separator
WS Whitespace
ON Other Neutrals
This property is always written in the compound form. For example, "\p{Bidi_Class:R}" matches characters that
are normally written right to left.
Scripts
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. 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" 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_Extensions", which is required to be written in
the compound form.)
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}/ # Matches
and only the first of these match:
"\N{KATAKANA-HIRAGANA DOUBLE HYPHEN}" =~ /\p{sc=Common} # Matches
"\N{KATAKANA-HIRAGANA DOUBLE HYPHEN}" =~ /\p{scx=Common} # No match
And 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} # Matches
"Script_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.
(Actually, besides "Common", the "Inherited" script, contains characters that are used in multiple scripts.
These are modifier characters which modify other characters, and 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
For backward compatibility (with Perl 5.6), all properties 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}".
Blocks
In addition to scripts, Unicode also defines blocks of characters. The difference between scripts and blocks
is that the concept of scripts is closer to natural languages, while the concept of blocks is more of an
artificial grouping based on groups of Unicode characters with consecutive ordinal values. For example, the
"Basic Latin" block is all 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":
<http://www.unicode.org/reports/tr24>
The "Script" or "Script_Extensions" 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. But Perl does provide a (slight)
shortcut: You can say, for example "\p{In_Arrows}" or "\p{In_Hebrew}". For backwards compatibility, the "In"
prefix may be omitted if there is no naming conflict with a script or any other property, and you can even use
an "Is" prefix instead in those cases. But it is not a good idea to do this, for a couple reasons:
1. It is confusing. There are many naming conflicts, and you may forget some. For example, "\p{Hebrew}"
means the script Hebrew, and NOT the block Hebrew. But would you remember that 6 months from now?
2. It is unstable. A new version of Unicode may pre-empt the current meaning by creating a property with the
same name. There was a time in very early Unicode releases when "\p{Hebrew}" would have matched the block
Hebrew; now it doesn't.
Some people prefer to always use "\p{Block: foo}" and "\p{Script: bar}" instead of the shortcuts, whether for
clarity, because they can't remember the difference between 'In' and 'Is' anyway, or they aren't confident
that those who eventually will read their code will know that difference.
A complete list of blocks and their shortcuts is in perluniprops.
Other Properties
There are many more properties than the very basic ones described here. A complete list is in perluniprops.
Unicode defines all its properties in the compound form, so all single-form properties are Perl extensions.
Most of these are just synonyms for the Unicode ones, but some are genuine extensions, including several that
are in the compound form. And quite a few of these are actually recommended by Unicode (in
<http://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
<http://www.unicode.org/reports/tr44>.
"\p{All}"
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 a non-canonical decomposition.
To understand the use of this rarely used property=value combination, it is necessary to know some basics
about decomposition. 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. This is called an "extended grapheme cluster"; Perl furnishes the
"\X" regular expression construct to match such sequences.
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. An
example is ISO-8859-1, which has quite a few of these in the Latin-1 range, an example being "LATIN
CAPITAL LETTER E WITH ACUTE". Because this character was in this pre-existing standard, Unicode added it
to its repertoire. 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
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.
However, many more characters have a different type of decomposition, a "compatible" or "non-canonical"
decomposition. The sequences that form these decompositions are not considered canonically equivalent to
the pre-composed character. An example, again in the Latin-1 range, 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" decomposition. There are several such compatibility
decompositions (see <http://www.unicode.org/reports/tr44>), including one called "compat", which means
some miscellaneous type of decomposition that doesn't fit into the decomposition categories that Unicode
has chosen.
Note that most Unicode characters don't have a decomposition, so their decomposition type is "None".
For your convenience, Perl has added the "Non_Canonical" decomposition type to mean any of the several
compatibility decompositions.
"\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=*}"
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 two digit Unicode version number, such as 1.1 or 4.0; 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 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{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.
if ($txt =~ /\p{IsForeign}+/) { ... }
Note that the effect is compile-time and immutable once defined. However, 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, and one set of values will
immutably be in effect for all case-sensitive matches, and the other set for all case-insensitive matches.
Note that if the regular expression is tainted, then Perl will die rather than calling the subroutine, where
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 Unicode code point to include.
· Two hexadecimal numbers separated by horizontal whitespace (space or tabular characters) denoting a range
of Unicode code points to include.
· 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
}
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.
(Note that official Unicode properties differ from these in that they automatically exclude non-Unicode code
points and a warning is raised if a match is attempted on one of those.)
User-Defined Case Mappings (for serious hackers only)
This feature has been removed as of Perl 5.16. The CPAN module Unicode::Casing provides better functionality
without the drawbacks that this feature had. If you are using a Perl earlier than 5.16, this feature was most
fully documented in the 5.14 version of this pod:
http://perldoc.perl.org/5.14.0/perlunicode.html#User-Defined-Case-Mappings-%28for-serious-hackers-only%29
<http://perldoc.perl.org/5.14.0/perlunicode.html#User-Defined-Case-Mappings-%28for-serious-hackers-only%29>
Character Encodings for Input and Output
See Encode.
Unicode Regular Expression Support Level
The following list of Unicode supported features for regular expressions describes all features currently
directly supported by core Perl. The references to "Level N" and the section numbers refer to the Unicode
Technical Standard #18, "Unicode Regular Expressions", version 13, from August 2008.
· Level 1 - Basic Unicode Support
RL1.1 Hex Notation - done [1]
RL1.2 Properties - done [2][3]
RL1.2a Compatibility Properties - done [4]
RL1.3 Subtraction and Intersection - MISSING [5]
operations
[6] \b \B
[7] note that Perl does Full case-folding in matching (but with
bugs), not Simple: for example U+1F88 is equivalent to
U+1F00 U+03B9, instead of just U+1F80. This difference
matters mainly for certain Greek capital letters with certain
modifiers: the Full case-folding decomposes the letter,
while the Simple case-folding would map it to a single
character.
[8] should do ^ and $ also on U+000B (\v in C), FF (\f), CR
(\r), CRLF (\r\n), NEL (U+0085), LS (U+2028), and PS
(U+2029); should also affect <>, $., and script line
numbers; should not split lines within CRLF [c] (i.e. there
is no empty line between \r and \n)
[9] Linebreaking conformant with UAX#14 "Unicode Line Breaking
Algorithm" is available through the Unicode::LineBreaking
module.
[10] UTF-8/UTF-EBDDIC used in Perl allows not only U+10000 to
U+10FFFF but also beyond U+10FFFF
[a] You can mimic class subtraction using lookahead. For example, what UTS#18 might write as
[{Greek}-[{UNASSIGNED}]]
in Perl can be written as:
(?!\p{Unassigned})\p{InGreekAndCoptic}
(?=\p{Assigned})\p{InGreekAndCoptic}
But in this particular example, you probably really want
\p{GreekAndCoptic}
which will match assigned characters known to be part of the Greek script.
Also see the Unicode::Regex::Set module; it does implement the full UTS#18 grouping, intersection, union,
and removal (subtraction) syntax.
[b] '+' for union, '-' for removal (set-difference), '&' for intersection (see "User-Defined Character
Properties")
[c] Try the ":crlf" layer (see PerlIO).
· Level 2 - Extended Unicode Support
RL2.1 Canonical Equivalents - MISSING [10][11]
RL2.2 Default Grapheme Clusters - MISSING [12]
RL2.3 Default Word Boundaries - MISSING [14]
RL2.4 Default Loose Matches - MISSING [15]
RL2.5 Name Properties - DONE
RL2.6 Wildcard Properties - MISSING
[10] see UAX#15 "Unicode Normalization Forms"
[11] have Unicode::Normalize but not integrated to regexes
RL3.7 Incremental Matches - MISSING
( RL3.8 Unicode Set Sharing )
RL3.9 Possible Match Sets - MISSING
RL3.10 Folded Matching - MISSING [20]
RL3.11 Submatchers - MISSING
[17] see UAX#10 "Unicode Collation Algorithms"
[18] have Unicode::Collate but not integrated to regexes
[19] have (?<=x) and (?=x), but look-aheads or look-behinds
should see outside of the target substring
[20] need insensitive matching for linguistic features other
than case; for example, hiragana to katakana, wide and
narrow, simplified Han to traditional Han (see UTR#30
"Character Foldings")
Unicode Encodings
Unicode characters are assigned to code points, which are abstract numbers. To use these numbers, various
encodings are needed.
· UTF-8
UTF-8 is a variable-length (1 to 4 bytes), byte-order independent encoding. For ASCII (and we really do
mean 7-bit ASCII, not another 8-bit encoding), UTF-8 is transparent.
The following table is from Unicode 3.2.
Code Points 1st Byte 2nd Byte 3rd Byte 4th Byte
U+0000..U+007F 00..7F
U+0080..U+07FF * C2..DF 80..BF
U+0800..U+0FFF E0 * A0..BF 80..BF
U+1000..U+CFFF E1..EC 80..BF 80..BF
U+D000..U+D7FF ED 80..9F 80..BF
U+D800..U+DFFF +++++ utf16 surrogates, not legal utf8 +++++
U+E000..U+FFFF EE..EF 80..BF 80..BF
U+10000..U+3FFFF F0 * 90..BF 80..BF 80..BF
U+40000..U+FFFFF F1..F3 80..BF 80..BF 80..BF
U+100000..U+10FFFF F4 80..8F 80..BF 80..BF
Note the gaps marked by "*" before several of the byte entries above. These are caused by legal UTF-8
avoiding non-shortest encodings: it is technically possible to UTF-8-encode a single code point in
different ways, but that is explicitly forbidden, and the shortest possible encoding should always be used
(and that is what Perl does).
Another way to look at it is via bits:
Code Points 1st Byte 2nd Byte 3rd Byte 4th Byte
0aaaaaaa 0aaaaaaa
00000bbbbbaaaaaa 110bbbbb 10aaaaaa
ccccbbbbbbaaaaaa 1110cccc 10bbbbbb 10aaaaaa
00000dddccccccbbbbbbaaaaaa 11110ddd 10cccccc 10bbbbbb 10aaaaaa
As you can see, the continuation bytes all begin with "10", and the leading bits of the start byte tell
Like UTF-8 but EBCDIC-safe, in the way that UTF-8 is ASCII-safe.
· UTF-16, UTF-16BE, UTF-16LE, Surrogates, and BOMs (Byte Order Marks)
The followings items are mostly for reference and general Unicode knowledge, Perl doesn't use these
constructs internally.
Like UTF-8, UTF-16 is a variable-width encoding, but where UTF-8 uses 8-bit code units, UTF-16 uses 16-bit
code units. All code points occupy either 2 or 4 bytes in UTF-16: code points "U+0000..U+FFFF" are stored
in a single 16-bit unit, and code points "U+10000..U+10FFFF" in two 16-bit units. 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 "U+10000..U+10FFFF" range of Unicode code points in
pairs of 16-bit units. The high surrogates are the range "U+D800..U+DBFF" and the low surrogates are the
range "U+DC00..U+DFFF". The surrogate encoding is
$hi = ($uni - 0x10000) / 0x400 + 0xD800;
$lo = ($uni - 0x10000) % 0x400 + 0xDC00;
and the decoding is
$uni = 0x10000 + ($hi - 0xD800) * 0x400 + ($lo - 0xDC00);
Because of the 16-bitness, UTF-16 is byte-order dependent. UTF-16 itself can be used for in-memory
computations, but if storage or transfer is required either UTF-16BE (big-endian) or UTF-16LE (little-
endian) encodings 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, or 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 "U+FEFF" 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 "U+FFFE" is not supposed to be in input
streams, so the sequence of bytes "0xFF 0xFE" is unambiguously "BOM, represented in little-endian format"
and cannot be "U+FFFE", represented in big-endian format".
Surrogates have no meaning in Unicode outside their use in pairs to represent other code points. However,
Perl allows them to be represented individually internally, for example by saying "chr(0xD801)", so that
all code points, not just those valid for open interchange, are representable. Unicode does define
semantics for them, such as their General Category is "Cs". But because their use is somewhat dangerous,
Perl will warn (using the warning category "surrogate", which is a sub-category of "utf8") if an attempt
is made to do things like take the lower case of one, or match case-insensitively, or to output them.
(But don't try this on Perls before 5.14.)
· UTF-32, UTF-32BE, UTF-32LE
The UTF-32 family is pretty much like the UTF-16 family, expect that the units are 32-bit, and therefore
the surrogate scheme is not needed. UTF-32 is a fixed-width encoding. The BOM signatures are "0x00 0x00
0xFE 0xFF" for BE and "0xFF 0xFE 0x00 0x00" for LE.
Non-character code points
66 code points are set aside in Unicode as "non-character code points". These all have the Unassigned (Cn)
General Category, and they never will be assigned. These are never supposed to be in legal Unicode input
streams, so that code can use them as sentinels that can be mixed in with character data, and they always will
be distinguishable from that data. To keep them out of Perl input streams, strict UTF-8 should be specified,
such as by using the layer ":encoding('UTF-8')". The non-character code points are the 32 between U+FDD0 and
U+FDEF, and the 34 code points U+FFFE, U+FFFF, U+1FFFE, U+1FFFF, ... U+10FFFE, U+10FFFF. Some people are
under the mistaken impression that these are "illegal", but that is not true. An application or cooperating
set of applications can legally use them at will internally; but these code points are "illegal for open
interchange". Therefore, Perl will not accept these from input streams unless lax rules are being used, and
will warn (using the warning category "nonchar", which is a sub-category of "utf8") if an attempt is made to
output them.
Beyond Unicode code points
The maximum Unicode code point is U+10FFFF. But Perl accepts code points up to the maximum permissible
unsigned number available on the platform. However, Perl will not accept these from input streams unless lax
rules are being used, and will warn (using the warning category "non_unicode", which is a sub-category of
"utf8") if an attempt is made to operate on or output them. For example, "uc(0x11_0000)" will generate this
warning, returning the input parameter as its result, as the upper case of every non-Unicode code point is the
code point itself.
Security Implications of Unicode
Read Unicode Security Considerations <http://www.unicode.org/reports/tr36>. Also, note the following:
· Malformed UTF-8
Unfortunately, the original 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, the shortest
possible sequence of UTF-8 bytes should be generated, because otherwise there is potential for an input
buffer overflow at the receiving end of a UTF-8 connection. Perl always generates the shortest length
UTF-8, and with warnings on, Perl will warn about non-shortest length UTF-8 along with other
malformations, such as the surrogates, which are not Unicode code points valid for interchange.
· Regular expression pattern matching may surprise you if you're not accustomed to Unicode. Starting in
Perl 5.14, several pattern modifiers are available to control this, called the character set modifiers.
Details are given in "Character set modifiers" in perlre.
As discussed elsewhere, Perl has one foot (two hooves?) planted in each of two worlds: the old world of bytes
and the new world of characters, upgrading from bytes to characters when necessary. If your legacy code does
not explicitly use Unicode, no automatic switch-over to characters should happen. Characters shouldn't get
downgraded to bytes, either. It is possible to accidentally mix bytes and characters, however (see
perluniintro), in which case "\w" in regular expressions might start behaving differently (unless the "/a"
modifier is in effect). Review your code. Use warnings and the "strict" pragma.
Unicode in Perl on EBCDIC
The way Unicode is handled on EBCDIC platforms is still experimental. On such platforms, references to UTF-8
encoding in this document and elsewhere should be read as meaning the UTF-EBCDIC 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 reused to mean the platform's "natural" 8-bit encoding
of Unicode. See perlebcdic for more discussion of the issues.
Locales
See "Unicode and UTF-8" in perllocale
"system": how well will the "command-line interface" (and which of them?) handle Unicode?
· chdir, chmod, chown, chroot, exec, link, lstat, mkdir, rename, rmdir, stat, symlink, truncate, unlink,
utime, -X
· %ENV
· glob (aka the <*>)
· open, opendir, sysopen
· qx (aka the backtick operator), system
· readdir, readlink
The "Unicode Bug"
The term, "Unicode bug" has been applied to an inconsistency on ASCII platforms with the Unicode code points
in the Latin-1 Supplement block, that is, between 128 and 255. Without a locale specified, unlike all other
characters or code points, these characters have very different semantics in byte semantics versus character
semantics, unless "use feature 'unicode_strings'" is specified, directly or indirectly. (It is indirectly
specified by a "use v5.12" or higher.)
In character semantics these upper-Latin1 characters are interpreted as Unicode code points, which means they
have the same semantics as Latin-1 (ISO-8859-1).
In byte semantics (without "unicode_strings"), they are considered to be unassigned characters, meaning that
the only semantics they have is their ordinal numbers, and that they are not members of various character
classes. None are considered to match "\w" for example, but all match "\W".
Perl 5.12.0 added "unicode_strings" to force character semantics on these code points in some circumstances,
which fixed portions of the bug; Perl 5.14.0 fixed almost all of it; and Perl 5.16.0 fixed the remainder (so
far as we know, anyway). The lesson here is to enable "unicode_strings" to avoid the headaches described
below.
The old, problematic behavior affects these areas:
· Changing the case of a scalar, that is, using "uc()", "ucfirst()", "lc()", and "lcfirst()", or "\L", "\U",
"\u" and "\l" in double-quotish contexts, such as regular expression substitutions. Under
"unicode_strings" starting in Perl 5.12.0, character semantics are generally used. See "lc" in perlfunc
for details on how this works in combination with various other pragmas.
· Using caseless ("/i") regular expression matching. Starting in Perl 5.14.0, regular expressions compiled
within the scope of "unicode_strings" use character semantics even when executed or compiled into larger
regular expressions outside the scope.
· Matching any of several properties in regular expressions, namely "\b", "\B", "\s", "\S", "\w", "\W", and
all the Posix character classes except "[[:ascii:]]". Starting in Perl 5.14.0, regular expressions
compiled within the scope of "unicode_strings" use character semantics even when executed or compiled into
larger regular expressions outside the scope.
· In "quotemeta" or its inline equivalent "\Q", no code points above 127 are quoted in UTF-8 encoded
strings, but in byte encoded strings, code points between 128-255 are always quoted. Starting in Perl
5.16.0, consistent quoting rules are used within the scope of "unicode_strings", as described in
"quotemeta" in perlfunc.
'
0
0
1
If there's no "\w" in "s1" or in "s2", why does their concatenation have one?
This anomaly stems from Perl's attempt to not disturb older programs that didn't use Unicode, and hence had no
semantics for characters outside of the ASCII range (except in a locale), along with Perl's desire to add
Unicode support seamlessly. The result wasn't seamless: these characters were orphaned.
For Perls earlier than those described above, or when a string is passed to a function outside the subpragma's
scope, a workaround is to always call "utf8::upgrade($string)", or to use the standard module Encode. Also,
a scalar that has any characters whose ordinal is above 0x100, or which were specified using either of the
"\N{...}" notations, will automatically have character semantics.
Forcing Unicode in Perl (Or Unforcing Unicode in Perl)
Sometimes (see "When Unicode Does Not Happen" or "The "Unicode Bug"") there are situations where you simply
need to force a byte string into UTF-8, or vice versa. The low-level calls utf8::upgrade($bytestring) and
utf8::downgrade($utf8string[, FAIL_OK]) are the answers.
Note that utf8::downgrade() can fail if the string contains characters that don't fit into a byte.
Calling either function on a string that already is in the desired state is a no-op.
Using Unicode in XS
If you want to handle Perl Unicode in XS extensions, you may find the following C APIs useful. See also
"Unicode Support" in perlguts for an explanation about Unicode at the XS level, and perlapi for the API
details.
· "DO_UTF8(sv)" returns true if the "UTF8" flag is on and the bytes pragma is not in effect. "SvUTF8(sv)"
returns true if 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
are even 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
code point 0..255 within the string. Perl's Unicode model is not to use UTF-8 until it is absolutely
necessary.
· "uvchr_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. It works appropriately on EBCDIC machines.
· "utf8_to_uvchr_buf(buf, bufend, 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. It works appropriately on
EBCDIC machines.
· "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
except that it does not set the "UTF8" flag. "sv_utf8_decode()" does the opposite of "sv_utf8_encode()".
Note that none of these are to be used as general-purpose encoding or decoding interfaces: "use Encode"
for that. "sv_utf8_upgrade()" is affected by the encoding pragma but "sv_utf8_downgrade()" is not (since
· "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 a 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 of the buffer if told to do so.
· "pv_uni_display(dsv, spv, len, pvlim, flags)" and "sv_uni_display(dsv, ssv, pvlim, flags)" are useful for
debugging the output of Unicode strings and scalars. By default they are useful only for debugging--they
display all characters as hexadecimal code points--but with the flags "UNI_DISPLAY_ISPRINT",
"UNI_DISPLAY_BACKSLASH", and "UNI_DISPLAY_QQ" you can make the output more readable.
· "foldEQ_utf8(s1, pe1, 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, except if one
string is in utf8 and the other isn't.
For more information, see perlapi, and utf8.c and utf8.h in the Perl source code distribution.
Hacking Perl to work on earlier Unicode versions (for very serious hackers only)
Perl by default comes with the latest supported Unicode version built in, but you can change to use any
earlier one.
Download the files in the desired version of Unicode from the Unicode web site <http://www.unicode.org>).
These should replace the existing files in lib/unicore in the Perl source tree. Follow the instructions in
README.perl in that directory to change some of their names, and then build perl (see INSTALL).
BUGS
Interaction with Locales
See "Unicode and UTF-8" in perllocale
Problems with characters in the Latin-1 Supplement range
See "The "Unicode Bug""
Interaction with Extensions
When Perl exchanges data with an extension, the extension should be able to understand the UTF8 flag and act
accordingly. If the extension doesn't recognize that flag, it's likely that the extension will return
incorrectly-flagged data.
So if you're working with Unicode data, consult the documentation of every module you're using if there are
any issues with Unicode data exchange. If the documentation does not talk about Unicode at all, suspect the
worst and probably look at the source to learn how the module is implemented. Modules written completely in
Perl shouldn't cause problems. Modules that directly or indirectly access code written in other programming
languages are at risk.
For affected functions, the simple strategy to avoid data corruption is to always make the encoding of the
exchanged data explicit. Choose an encoding that you know the extension can handle. Convert arguments passed
to the extensions to that encoding and convert results back from that encoding. Write wrapper functions that
do the conversions for you, so you can later change the functions when the extension catches up.
To provide an example, let's say the popular Foo::Bar::escape_html function doesn't deal with Unicode data
yet. The wrapper function would convert the argument to raw UTF-8 and convert the result back to Perl's
internal representation like so:
sub my_escape_html ($) {
If it does not yet provide support for any encoding, one could write a derived class with such a "param"
method:
sub param {
my($self,$name,$value) = @_;
utf8::upgrade($name); # make sure it is UTF-8 encoded
if (defined $value) {
utf8::upgrade($value); # make sure it is UTF-8 encoded
return $self->SUPER::param($name,$value);
} else {
my $ret = $self->SUPER::param($name);
Encode::_utf8_on($ret); # we know, it is UTF-8 encoded
return $ret;
}
}
Some extensions provide filters on data entry/exit points, such as DB_File::filter_store_key and family. Look
out for such filters in the documentation of your extensions, they can make the transition to Unicode data
much easier.
Speed
Some functions are slower when working on UTF-8 encoded strings than on byte encoded strings. All functions
that need to hop over characters such as length(), substr() or index(), or matching regular expressions can
work much faster when the underlying data are byte-encoded.
In Perl 5.8.0 the slowness was often quite spectacular; in Perl 5.8.1 a caching scheme was introduced which
will hopefully make the slowness somewhat less spectacular, at least for some operations. In general,
operations with UTF-8 encoded strings are still slower. As an example, the Unicode properties (character
classes) like "\p{Nd}" are known to be quite a bit slower (5-20 times) than their simpler counterparts like
"\d" (then again, there are hundreds of Unicode characters matching "Nd" compared with the 10 ASCII characters
matching "d").
Problems on EBCDIC platforms
There are several known problems with Perl on EBCDIC platforms. If you want to use Perl there, send email to
[email protected].
In earlier versions, when byte and character data were concatenated, the new string was sometimes created by
decoding the byte strings as ISO 8859-1 (Latin-1), even if the old Unicode string used EBCDIC.
If you find any of these, please report them as bugs.
Porting code from perl-5.6.X
Perl 5.8 has a different Unicode model from 5.6. In 5.6 the programmer was required to use the "utf8" pragma
to declare that a given scope expected to deal with Unicode data and had to make sure that only Unicode data
were reaching that scope. If you have code that is working with 5.6, you will need some of the following
adjustments to your code. The examples are written such that the code will continue to work under 5.6, so you
should be safe to try them out.
· A filehandle that should read or write UTF-8
if ($] > 5.007) {
binmode $fh, ":encoding(utf8)";
}
· A scalar we got back from an extension
If you believe the scalar comes back as UTF-8, you will most likely want the UTF8 flag restored:
if ($] > 5.007) {
require Encode;
$val = Encode::decode_utf8($val);
}
· Same thing, if you are really sure it is UTF-8
if ($] > 5.007) {
require Encode;
Encode::_utf8_on($val);
}
· A wrapper for fetchrow_array and fetchrow_hashref
When the database contains only UTF-8, a wrapper function or method is a convenient way to replace all your
fetchrow_array and fetchrow_hashref calls. A wrapper function will also make it easier to adapt to future
enhancements in your database driver. Note that at the time of this writing (October 2002), the DBI has no
standardized way to deal with UTF-8 data. Please check the documentation to verify if that is still true.
sub fetchrow {
# $what is one of fetchrow_{array,hashref}
my($self, $sth, $what) = @_;
if ($] < 5.007) {
return $sth->$what;
} else {
require Encode;
if (wantarray) {
my @arr = $sth->$what;
for (@arr) {
defined && /[^\000-\177]/ && Encode::_utf8_on($_);
}
return @arr;
} else {
my $ret = $sth->$what;
if (ref $ret) {
for my $k (keys %$ret) {
defined
&& /[^\000-\177]/
&& Encode::_utf8_on($_) for $ret->{$k};
}
return $ret;
} else {
defined && /[^\000-\177]/ && Encode::_utf8_on($_) for $ret;
return $ret;
}
}
}
}
· A large scalar that you know can only contain ASCII
perl v5.16.3 2013-03-04 PERLUNICODE(1)
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