PERLUNIINTRO(1) Perl Programmers Reference Guide PERLUNIINTRO(1)
NAME
perluniintro - Perl Unicode introduction
DESCRIPTION
This document gives a general idea of Unicode and how to use Unicode in
Perl. See "Further Resources" for references to more in-depth
treatments of Unicode.
Unicode
Unicode is a character set standard which plans to codify all of the
writing systems of the world, plus many other symbols.
Unicode and ISO/IEC 10646 are coordinated standards that unify almost
all other modern character set standards, covering more than 80 writing
systems and hundreds of languages, including all commercially-important
modern languages. All characters in the largest Chinese, Japanese, and
Korean dictionaries are also encoded. The standards will eventually
cover almost all characters in more than 250 writing systems and
thousands of languages. Unicode 1.0 was released in October 1991, and
6.0 in October 2010.
A Unicode character is an abstract entity. It is not bound to any
particular integer width, especially not to the C language "char".
Unicode is language-neutral and display-neutral: it does not encode the
language of the text, and it does not generally define fonts or other
graphical layout details. Unicode operates on characters and on text
built from those characters.
Unicode defines characters like "LATIN CAPITAL LETTER A" or "GREEK SMALL
LETTER ALPHA" and unique numbers for the characters, in this case 0x0041
and 0x03B1, respectively. These unique numbers are called code points.
A code point is essentially the position of the character within the set
of all possible Unicode characters, and thus in Perl, the term ordinal
is often used interchangeably with it.
The Unicode standard prefers using hexadecimal notation for the code
points. If numbers like 0x0041 are unfamiliar to you, take a peek at a
later section, "Hexadecimal Notation". The Unicode standard uses the
notation "U+0041 LATIN CAPITAL LETTER A", to give the hexadecimal code
point and the normative name of the character.
Unicode also defines various properties for the characters, like
"uppercase" or "lowercase", "decimal digit", or "punctuation"; these
properties are independent of the names of the characters. Furthermore,
various operations on the characters like uppercasing, lowercasing, and
collating (sorting) are defined.
A Unicode logical "character" can actually consist of more than one
internal actual "character" or code point. For Western languages, this
is adequately modelled by a base character (like "LATIN CAPITAL LETTER
A") followed by one or more modifiers (like "COMBINING ACUTE ACCENT").
This sequence of base character and modifiers is called a combining
character sequence. Some non-western languages require more complicated
models, so Unicode created the grapheme cluster concept, which was later
further refined into the extended grapheme cluster. For example, a
Korean Hangul syllable is considered a single logical character, but
most often consists of three actual Unicode characters: a leading
consonant followed by an interior vowel followed by a trailing
consonant.
Whether to call these extended grapheme clusters "characters" depends on
your point of view. If you are a programmer, you probably would tend
towards seeing each element in the sequences as one unit, or
"character". However from the user's point of view, the whole sequence
could be seen as one "character" since that's probably what it looks
like in the context of the user's language. In this document, we take
the programmer's point of view: one "character" is one Unicode code
point.
For some combinations of base character and modifiers, there are
precomposed characters. There is a single character equivalent, for
example, for the sequence "LATIN CAPITAL LETTER A" followed by
"COMBINING ACUTE ACCENT". It is called "LATIN CAPITAL LETTER A WITH
ACUTE". These precomposed characters are, however, only available for
some combinations, and are mainly meant to support round-trip
conversions between Unicode and legacy standards (like ISO 8859). Using
sequences, as Unicode does, allows for needing fewer basic building
blocks (code points) to express many more potential grapheme clusters.
To support conversion between equivalent forms, various normalization
forms are also defined. Thus, "LATIN CAPITAL LETTER A WITH ACUTE" is in
Normalization Form Composed, (abbreviated NFC), and the sequence "LATIN
CAPITAL LETTER A" followed by "COMBINING ACUTE ACCENT" represents the
same character in Normalization Form Decomposed (NFD).
Because of backward compatibility with legacy encodings, the "a unique
number for every character" idea breaks down a bit: instead, there is
"at least one number for every character". The same character could be
represented differently in several legacy encodings. The converse is
not true: some code points do not have an assigned character. Firstly,
there are unallocated code points within otherwise used blocks.
Secondly, there are special Unicode control characters that do not
represent true characters.
When Unicode was first conceived, it was thought that all the world's
characters could be represented using a 16-bit word; that is a maximum
of 0x10000 (or 65,536) characters would be needed, from 0x0000 to
0xFFFF. This soon proved to be wrong, and since Unicode 2.0 (July
1996), Unicode has been defined all the way up to 21 bits (0x10FFFF),
and Unicode 3.1 (March 2001) defined the first characters above 0xFFFF.
The first 0x10000 characters are called the Plane 0, or the Basic
Multilingual Plane (BMP). With Unicode 3.1, 17 (yes, seventeen) planes
in all were defined--but they are nowhere near full of defined
characters, yet.
When a new language is being encoded, Unicode generally will choose a
"block" of consecutive unallocated code points for its characters. So
far, the number of code points in these blocks has always been evenly
divisible by 16. Extras in a block, not currently needed, are left
unallocated, for future growth. But there have been occasions when a
later release needed more code points than the available extras, and a
new block had to allocated somewhere else, not contiguous to the initial
one, to handle the overflow. Thus, it became apparent early on that
"block" wasn't an adequate organizing principle, and so the "Script"
property was created. (Later an improved script property was added as
well, the "Script_Extensions" property.) Those code points that are in
overflow blocks can still have the same script as the original ones.
The script concept fits more closely with natural language: there is
"Latin" script, "Greek" script, and so on; and there are several
artificial scripts, like "Common" for characters that are used in
multiple scripts, such as mathematical symbols. Scripts usually span
varied parts of several blocks. For more information about scripts, see
"Scripts" in perlunicode. The division into blocks exists, but it is
almost completely accidental--an artifact of how the characters have
been and still are allocated. (Note that this paragraph has
oversimplified things for the sake of this being an introduction.
Unicode doesn't really encode languages, but the writing systems for
them--their scripts; and one script can be used by many languages.
Unicode also encodes things that aren't really about languages, such as
symbols like "BAGGAGE CLAIM".)
The Unicode code points are just abstract numbers. To input and output
these abstract numbers, the numbers must be encoded or serialised
somehow. Unicode defines several character encoding forms, of which
UTF-8 is the most popular. UTF-8 is a variable length encoding that
encodes Unicode characters as 1 to 4 bytes. Other encodings include
UTF-16 and UTF-32 and their big- and little-endian variants (UTF-8 is
byte-order independent). The ISO/IEC 10646 defines the UCS-2 and UCS-4
encoding forms.
For more information about encodings--for instance, to learn what
surrogates and byte order marks (BOMs) are--see perlunicode.
Perl's Unicode Support
Starting from Perl v5.6.0, Perl has had the capacity to handle Unicode
natively. Perl v5.8.0, however, is the first recommended release for
serious Unicode work. The maintenance release 5.6.1 fixed many of the
problems of the initial Unicode implementation, but for example regular
expressions still do not work with Unicode in 5.6.1. Perl v5.14.0 is
the first release where Unicode support is (almost) seamlessly
integratable without some gotchas. (There are a few exceptions. Firstly,
some differences in quotemeta were fixed starting in Perl 5.16.0.
Secondly, some differences in the range operator were fixed starting in
Perl 5.26.0. Thirdly, some differences in split were fixed started in
Perl 5.28.0.)
To enable this seamless support, you should "use feature
'unicode_strings'" (which is automatically selected if you "use v5.12"
or higher). See feature. (5.14 also fixes a number of bugs and
departures from the Unicode standard.)
Before Perl v5.8.0, the use of "use utf8" was used to declare that
operations in the current block or file would be Unicode-aware. This
model was found to be wrong, or at least clumsy: the "Unicodeness" is
now carried with the data, instead of being attached to the operations.
Starting with Perl v5.8.0, only one case remains where an explicit "use
utf8" is needed: if your Perl script itself is encoded in UTF-8, you can
use UTF-8 in your identifier names, and in string and regular expression
literals, by saying "use utf8". This is not the default because scripts
with legacy 8-bit data in them would break. See utf8.
Perl's Unicode Model
Perl supports both pre-5.6 strings of eight-bit native bytes, and
strings of Unicode characters. The general principle is that Perl tries
to keep its data as eight-bit bytes for as long as possible, but as soon
as Unicodeness cannot be avoided, the data is transparently upgraded to
Unicode. Prior to Perl v5.14.0, the upgrade was not completely
transparent (see "The "Unicode Bug"" in perlunicode), and for backwards
compatibility, full transparency is not gained unless use feature
'unicode_strings' (see feature) or "use v5.12" (or higher) is selected.
Internally, Perl currently uses either whatever the native eight-bit
character set of the platform (for example Latin-1) is, defaulting to
UTF-8, to encode Unicode strings. Specifically, if all code points in
the string are 0xFF or less, Perl uses the native eight-bit character
set. Otherwise, it uses UTF-8.
A user of Perl does not normally need to know nor care how Perl happens
to encode its internal strings, but it becomes relevant when outputting
Unicode strings to a stream without a PerlIO layer (one with the
"default" encoding). In such a case, the raw bytes used internally (the
native character set or UTF-8, as appropriate for each string) will be
used, and a "Wide character" warning will be issued if those strings
contain a character beyond 0x00FF.
For example,
perl -e 'print "\x{DF}\n", "\x{0100}\x{DF}\n"'
produces a fairly useless mixture of native bytes and UTF-8, as well as
a warning:
Wide character in print at ...
To output UTF-8, use the ":encoding" or ":utf8" output layer.
Prepending
binmode(STDOUT, ":utf8");
to this sample program ensures that the output is completely UTF-8, and
removes the program's warning.
You can enable automatic UTF-8-ification of your standard file handles,
default open() layer, and @ARGV by using either the "-C" command line
switch or the "PERL_UNICODE" environment variable, see perlrun for the
documentation of the "-C" switch.
Note that this means that Perl expects other software to work the same
way: if Perl has been led to believe that STDIN should be UTF-8, but
then STDIN coming in from another command is not UTF-8, Perl will likely
complain about the malformed UTF-8.
All features that combine Unicode and I/O also require using the new
PerlIO feature. Almost all Perl 5.8 platforms do use PerlIO, though:
you can see whether yours is by running "perl -V" and looking for
"useperlio=define".
Unicode and EBCDIC
Perl 5.8.0 added support for Unicode on EBCDIC platforms. This support
was allowed to lapse in later releases, but was revived in 5.22.
Unicode support is somewhat more complex to implement since additional
conversions are needed. See perlebcdic for more information.
On EBCDIC platforms, the internal Unicode encoding form is UTF-EBCDIC
instead of UTF-8. The difference is that as UTF-8 is "ASCII-safe" in
that ASCII characters encode to UTF-8 as-is, while UTF-EBCDIC is
"EBCDIC-safe", in that all the basic characters (which includes all
those that have ASCII equivalents (like "A", "0", "%", etc.) are the
same in both EBCDIC and UTF-EBCDIC. Often, documentation will use the
term "UTF-8" to mean UTF-EBCDIC as well. This is the case in this
document.
Creating Unicode
This section applies fully to Perls starting with v5.22. Various
caveats for earlier releases are in the "Earlier releases caveats"
subsection below.
To create Unicode characters in literals, use the "\N{...}" notation in
double-quoted strings:
my $smiley_from_name = "\N{WHITE SMILING FACE}";
my $smiley_from_code_point = "\N{U+263a}";
Similarly, they can be used in regular expression literals
$smiley =~ /\N{WHITE SMILING FACE}/;
$smiley =~ /\N{U+263a}/;
or, starting in v5.32:
$smiley =~ /\p{Name=WHITE SMILING FACE}/;
$smiley =~ /\p{Name=whitesmilingface}/;
At run-time you can use:
use charnames ();
my $hebrew_alef_from_name
= charnames::string_vianame("HEBREW LETTER ALEF");
my $hebrew_alef_from_code_point = charnames::string_vianame("U+05D0");
Naturally, ord() will do the reverse: it turns a character into a code
point.
There are other runtime options as well. You can use pack():
my $hebrew_alef_from_code_point = pack("U", 0x05d0);
Or you can use chr(), though it is less convenient in the general case:
$hebrew_alef_from_code_point = chr(utf8::unicode_to_native(0x05d0));
utf8::upgrade($hebrew_alef_from_code_point);
The utf8::unicode_to_native() and utf8::upgrade() aren't needed if the
argument is above 0xFF, so the above could have been written as
$hebrew_alef_from_code_point = chr(0x05d0);
since 0x5d0 is above 255.
"\x{}" and "\o{}" can also be used to specify code points at compile
time in double-quotish strings, but, for backward compatibility with
older Perls, the same rules apply as with chr() for code points less
than 256.
utf8::unicode_to_native() is used so that the Perl code is portable to
EBCDIC platforms. You can omit it if you're really sure no one will
ever want to use your code on a non-ASCII platform. Starting in Perl
v5.22, calls to it on ASCII platforms are optimized out, so there's no
performance penalty at all in adding it. Or you can simply use the
other constructs that don't require it.
See "Further Resources" for how to find all these names and numeric
codes.
Earlier releases caveats
On EBCDIC platforms, prior to v5.22, using "\N{U+...}" doesn't work
properly.
Prior to v5.16, using "\N{...}" with a character name (as opposed to a
"U+..." code point) required a "use charnames :full".
Prior to v5.14, there were some bugs in "\N{...}" with a character name
(as opposed to a "U+..." code point).
charnames::string_vianame() was introduced in v5.14. Prior to that,
charnames::vianame() should work, but only if the argument is of the
form "U+...". Your best bet there for runtime Unicode by character name
is probably:
use charnames ();
my $hebrew_alef_from_name
= pack("U", charnames::vianame("HEBREW LETTER ALEF"));
Handling Unicode
Handling Unicode is for the most part transparent: just use the strings
as usual. Functions like index(), length(), and substr() will work on
the Unicode characters; regular expressions will work on the Unicode
characters (see perlunicode and perlretut).
Note that Perl considers grapheme clusters to be separate characters, so
for example
print length("\N{LATIN CAPITAL LETTER A}\N{COMBINING ACUTE ACCENT}"),
"\n";
will print 2, not 1. The only exception is that regular expressions
have "\X" for matching an extended grapheme cluster. (Thus "\X" in a
regular expression would match the entire sequence of both the example
characters.)
Life is not quite so transparent, however, when working with legacy
encodings, I/O, and certain special cases:
Legacy Encodings
When you combine legacy data and Unicode, the legacy data needs to be
upgraded to Unicode. Normally the legacy data is assumed to be ISO
8859-1 (or EBCDIC, if applicable).
The "Encode" module knows about many encodings and has interfaces for
doing conversions between those encodings:
use Encode 'decode';
$data = decode("iso-8859-3", $data); # convert from legacy
Unicode I/O
Normally, writing out Unicode data
print FH $some_string_with_unicode, "\n";
produces raw bytes that Perl happens to use to internally encode the
Unicode string. Perl's internal encoding depends on the system as well
as what characters happen to be in the string at the time. If any of the
characters are at code points 0x100 or above, you will get a warning.
To ensure that the output is explicitly rendered in the encoding you
desire--and to avoid the warning--open the stream with the desired
encoding. Some examples:
open FH, ">:utf8", "file";
open FH, ">:encoding(ucs2)", "file";
open FH, ">:encoding(UTF-8)", "file";
open FH, ">:encoding(shift_jis)", "file";
and on already open streams, use binmode():
binmode(STDOUT, ":utf8");
binmode(STDOUT, ":encoding(ucs2)");
binmode(STDOUT, ":encoding(UTF-8)");
binmode(STDOUT, ":encoding(shift_jis)");
The matching of encoding names is loose: case does not matter, and many
encodings have several aliases. Note that the ":utf8" layer must always
be specified exactly like that; it is not subject to the loose matching
of encoding names. Also note that currently ":utf8" is unsafe for input,
because it accepts the data without validating that it is indeed valid
UTF-8; you should instead use :encoding(UTF-8) (with or without a
hyphen).
See PerlIO for the ":utf8" layer, PerlIO::encoding and Encode::PerlIO
for the :encoding() layer, and Encode::Supported for many encodings
supported by the "Encode" module.
Reading in a file that you know happens to be encoded in one of the
Unicode or legacy encodings does not magically turn the data into
Unicode in Perl's eyes. To do that, specify the appropriate layer when
opening files
open(my $fh,'<:encoding(UTF-8)', 'anything');
my $line_of_unicode = <$fh>;
open(my $fh,'<:encoding(Big5)', 'anything');
my $line_of_unicode = <$fh>;
The I/O layers can also be specified more flexibly with the "open"
pragma. See open, or look at the following example.
use open ':encoding(UTF-8)'; # input/output default encoding will be
# UTF-8
open X, ">file";
print X chr(0x100), "\n";
close X;
open Y, "<file";
printf "%#x\n", ord(<Y>); # this should print 0x100
close Y;
With the "open" pragma you can use the ":locale" layer
BEGIN { $ENV{LC_ALL} = $ENV{LANG} = 'ru_RU.KOI8-R' }
# the :locale will probe the locale environment variables like
# LC_ALL
use open OUT => ':locale'; # russki parusski
open(O, ">koi8");
print O chr(0x430); # Unicode CYRILLIC SMALL LETTER A = KOI8-R 0xc1
close O;
open(I, "<koi8");
printf "%#x\n", ord(<I>), "\n"; # this should print 0xc1
close I;
These methods install a transparent filter on the I/O stream that
converts data from the specified encoding when it is read in from the
stream. The result is always Unicode.
The open pragma affects all the open() calls after the pragma by setting
default layers. If you want to affect only certain streams, use
explicit layers directly in the open() call.
You can switch encodings on an already opened stream by using binmode();
see "binmode" in perlfunc.
The ":locale" does not currently work with open() and binmode(), only
with the "open" pragma. The ":utf8" and :encoding(...) methods do work
with all of open(), binmode(), and the "open" pragma.
Similarly, you may use these I/O layers on output streams to
automatically convert Unicode to the specified encoding when it is
written to the stream. For example, the following snippet copies the
contents of the file "text.jis" (encoded as ISO-2022-JP, aka JIS) to the
file "text.utf8", encoded as UTF-8:
open(my $nihongo, '<:encoding(iso-2022-jp)', 'text.jis');
open(my $unicode, '>:utf8', 'text.utf8');
while (<$nihongo>) { print $unicode $_ }
The naming of encodings, both by the open() and by the "open" pragma
allows for flexible names: "koi8-r" and "KOI8R" will both be understood.
Common encodings recognized by ISO, MIME, IANA, and various other
standardisation organisations are recognised; for a more detailed list
see Encode::Supported.
read() reads characters and returns the number of characters. seek()
and tell() operate on byte counts, as does sysseek().
sysread() and syswrite() should not be used on file handles with
character encoding layers, they behave badly, and that behaviour has
been deprecated since perl 5.24.
Notice that because of the default behaviour of not doing any conversion
upon input if there is no default layer, it is easy to mistakenly write
code that keeps on expanding a file by repeatedly encoding the data:
# BAD CODE WARNING
open F, "file";
local $/; ## read in the whole file of 8-bit characters
$t = <F>;
close F;
open F, ">:encoding(UTF-8)", "file";
print F $t; ## convert to UTF-8 on output
close F;
If you run this code twice, the contents of the file will be twice UTF-8
encoded. A "use open ':encoding(UTF-8)'" would have avoided the bug, or
explicitly opening also the file for input as UTF-8.
NOTE: the ":utf8" and ":encoding" features work only if your Perl has
been built with PerlIO, which is the default on most systems.
Displaying Unicode As Text
Sometimes you might want to display Perl scalars containing Unicode as
simple ASCII (or EBCDIC) text. The following subroutine converts its
argument so that Unicode characters with code points greater than 255
are displayed as "\x{...}", control characters (like "\n") are displayed
as "\x..", and the rest of the characters as themselves:
sub nice_string {
join("",
map { $_ > 255 # if wide character...
? sprintf("\\x{%04X}", $_) # \x{...}
: chr($_) =~ /[[:cntrl:]]/ # else if control character...
? sprintf("\\x%02X", $_) # \x..
: quotemeta(chr($_)) # else quoted or as themselves
} unpack("W*", $_[0])); # unpack Unicode characters
}
For example,
nice_string("foo\x{100}bar\n")
returns the string
'foo\x{0100}bar\x0A'
which is ready to be printed.
("\\x{}" is used here instead of "\\N{}", since it's most likely that
you want to see what the native values are.)
Special Cases
• Starting in Perl 5.28, it is illegal for bit operators, like "~", to
operate on strings containing code points above 255.
• The vec() function may produce surprising results if used on strings
containing characters with ordinal values above 255. In such a case,
the results are consistent with the internal encoding of the
characters, but not with much else. So don't do that, and starting
in Perl 5.28, a deprecation message is issued if you do so, becoming
illegal in Perl 5.32.
• Peeking At Perl's Internal Encoding
Normal users of Perl should never care how Perl encodes any
particular Unicode string (because the normal ways to get at the
contents of a string with Unicode--via input and output--should
always be via explicitly-defined I/O layers). But if you must, there
are two ways of looking behind the scenes.
One way of peeking inside the internal encoding of Unicode
characters is to use "unpack("C*", ..." to get the bytes of whatever
the string encoding happens to be, or "unpack("U0..", ...)" to get
the bytes of the UTF-8 encoding:
# this prints c4 80 for the UTF-8 bytes 0xc4 0x80
print join(" ", unpack("U0(H2)*", pack("U", 0x100))), "\n";
Yet another way would be to use the Devel::Peek module:
perl -MDevel::Peek -e 'Dump(chr(0x100))'
That shows the "UTF8" flag in FLAGS and both the UTF-8 bytes and
Unicode characters in "PV". See also later in this document the
discussion about the utf8::is_utf8() function.
Advanced Topics
• String Equivalence
The question of string equivalence turns somewhat complicated in
Unicode: what do you mean by "equal"?
(Is "LATIN CAPITAL LETTER A WITH ACUTE" equal to "LATIN CAPITAL
LETTER A"?)
The short answer is that by default Perl compares equivalence ("eq",
"ne") based only on code points of the characters. In the above
case, the answer is no (because 0x00C1 != 0x0041). But sometimes,
any CAPITAL LETTER A's should be considered equal, or even A's of
any case.
The long answer is that you need to consider character normalization
and casing issues: see Unicode::Normalize, Unicode Technical Report
#15, Unicode Normalization Forms
<https://www.unicode.org/reports/tr15> and sections on case mapping
in the Unicode Standard <https://www.unicode.org>.
As of Perl 5.8.0, the "Full" case-folding of Case
Mappings/SpecialCasing is implemented, but bugs remain in "qr//i"
with them, mostly fixed by 5.14, and essentially entirely by 5.18.
• String Collation
People like to see their strings nicely sorted--or as Unicode
parlance goes, collated. But again, what do you mean by collate?
(Does "LATIN CAPITAL LETTER A WITH ACUTE" come before or after
"LATIN CAPITAL LETTER A WITH GRAVE"?)
The short answer is that by default, Perl compares strings ("lt",
"le", "cmp", "ge", "gt") based only on the code points of the
characters. In the above case, the answer is "after", since 0x00C1
> 0x00C0.
The long answer is that "it depends", and a good answer cannot be
given without knowing (at the very least) the language context. See
Unicode::Collate, and Unicode Collation Algorithm
<https://www.unicode.org/reports/tr10/>
Miscellaneous
• Character Ranges and Classes
Character ranges in regular expression bracketed character classes (
e.g., "/[a-z]/") and in the "tr///" (also known as "y///") operator
are not magically Unicode-aware. What this means is that "[A-Za-z]"
will not magically start to mean "all alphabetic letters" (not that
it does mean that even for 8-bit characters; for those, if you are
using locales (perllocale), use "/[[:alpha:]]/"; and if not, use the
8-bit-aware property "\p{alpha}").
All the properties that begin with "\p" (and its inverse "\P") are
actually character classes that are Unicode-aware. There are dozens
of them, see perluniprops.
Starting in v5.22, you can use Unicode code points as the end points
of regular expression pattern character ranges, and the range will
include all Unicode code points that lie between those end points,
inclusive.
qr/ [ \N{U+03} - \N{U+20} ] /xx
includes the code points "\N{U+03}", "\N{U+04}", ..., "\N{U+20}".
This also works for ranges in "tr///" starting in Perl v5.24.
• String-To-Number Conversions
Unicode does define several other decimal--and numeric--characters
besides the familiar 0 to 9, such as the Arabic and Indic digits.
Perl does not support string-to-number conversion for digits other
than ASCII 0 to 9 (and ASCII "a" to "f" for hexadecimal). To get
safe conversions from any Unicode string, use "num()" in
Unicode::UCD.
Questions With Answers
• Will My Old Scripts Break?
Very probably not. Unless you are generating Unicode characters
somehow, old behaviour should be preserved. About the only
behaviour that has changed and which could start generating Unicode
is the old behaviour of chr() where supplying an argument more than
255 produced a character modulo 255. chr(300), for example, was
equal to chr(45) or "-" (in ASCII), now it is LATIN CAPITAL LETTER I
WITH BREVE.
• How Do I Make My Scripts Work With Unicode?
Very little work should be needed since nothing changes until you
generate Unicode data. The most important thing is getting input as
Unicode; for that, see the earlier I/O discussion. To get full
seamless Unicode support, add "use feature 'unicode_strings'" (or
"use v5.12" or higher) to your script.
• How Do I Know Whether My String Is In Unicode?
You shouldn't have to care. But you may if your Perl is before
5.14.0 or you haven't specified "use feature 'unicode_strings'" or
use 5.012 (or higher) because otherwise the rules for the code
points in the range 128 to 255 are different depending on whether
the string they are contained within is in Unicode or not. (See
"When Unicode Does Not Happen" in perlunicode.)
To determine if a string is in Unicode, use:
print utf8::is_utf8($string) ? 1 : 0, "\n";
But note that this doesn't mean that any of the characters in the
string are necessary UTF-8 encoded, or that any of the characters
have code points greater than 0xFF (255) or even 0x80 (128), or that
the string has any characters at all. All the is_utf8() does is to
return the value of the internal "utf8ness" flag attached to the
$string. If the flag is off, the bytes in the scalar are
interpreted as a single byte encoding. If the flag is on, the bytes
in the scalar are interpreted as the (variable-length, potentially
multi-byte) UTF-8 encoded code points of the characters. Bytes
added to a UTF-8 encoded string are automatically upgraded to UTF-8.
If mixed non-UTF-8 and UTF-8 scalars are merged (double-quoted
interpolation, explicit concatenation, or printf/sprintf parameter
substitution), the result will be UTF-8 encoded as if copies of the
byte strings were upgraded to UTF-8: for example,
$x = "ab\x80c";
$y = "\x{100}";
print "$x = $y\n";
the output string will be UTF-8-encoded "ab\x80c = \x{100}\n", but
$x will stay byte-encoded.
Sometimes you might really need to know the byte length of a string
instead of the character length. For that use the "bytes" pragma and
the length() function:
my $unicode = chr(0x100);
print length($unicode), "\n"; # will print 1
use bytes;
print length($unicode), "\n"; # will print 2
# (the 0xC4 0x80 of the UTF-8)
no bytes;
• How Do I Find Out What Encoding a File Has?
You might try Encode::Guess, but it has a number of limitations.
• How Do I Detect Data That's Not Valid In a Particular Encoding?
Use the "Encode" package to try converting it. For example,
use Encode 'decode';
if (eval { decode('UTF-8', $string, Encode::FB_CROAK); 1 }) {
# $string is valid UTF-8
} else {
# $string is not valid UTF-8
}
Or use "unpack" to try decoding it:
use warnings;
@chars = unpack("C0U*", $string_of_bytes_that_I_think_is_utf8);
If invalid, a "Malformed UTF-8 character" warning is produced. The
"C0" means "process the string character per character". Without
that, the "unpack("U*", ...)" would work in "U0" mode (the default
if the format string starts with "U") and it would return the bytes
making up the UTF-8 encoding of the target string, something that
will always work.
• How Do I Convert Binary Data Into a Particular Encoding, Or Vice
Versa?
This probably isn't as useful as you might think. Normally, you
shouldn't need to.
In one sense, what you are asking doesn't make much sense: encodings
are for characters, and binary data are not "characters", so
converting "data" into some encoding isn't meaningful unless you
know in what character set and encoding the binary data is in, in
which case it's not just binary data, now is it?
If you have a raw sequence of bytes that you know should be
interpreted via a particular encoding, you can use "Encode":
use Encode 'from_to';
from_to($data, "iso-8859-1", "UTF-8"); # from latin-1 to UTF-8
The call to from_to() changes the bytes in $data, but nothing
material about the nature of the string has changed as far as Perl
is concerned. Both before and after the call, the string $data
contains just a bunch of 8-bit bytes. As far as Perl is concerned,
the encoding of the string remains as "system-native 8-bit bytes".
You might relate this to a fictional 'Translate' module:
use Translate;
my $phrase = "Yes";
Translate::from_to($phrase, 'english', 'deutsch');
## phrase now contains "Ja"
The contents of the string changes, but not the nature of the
string. Perl doesn't know any more after the call than before that
the contents of the string indicates the affirmative.
Back to converting data. If you have (or want) data in your
system's native 8-bit encoding (e.g. Latin-1, EBCDIC, etc.), you can
use pack/unpack to convert to/from Unicode.
$native_string = pack("W*", unpack("U*", $Unicode_string));
$Unicode_string = pack("U*", unpack("W*", $native_string));
If you have a sequence of bytes you know is valid UTF-8, but Perl
doesn't know it yet, you can make Perl a believer, too:
$Unicode = $bytes;
utf8::decode($Unicode);
or:
$Unicode = pack("U0a*", $bytes);
You can find the bytes that make up a UTF-8 sequence with
@bytes = unpack("C*", $Unicode_string)
and you can create well-formed Unicode with
$Unicode_string = pack("U*", 0xff, ...)
• How Do I Display Unicode? How Do I Input Unicode?
See <http://www.alanwood.net/unicode/> and
<http://www.cl.cam.ac.uk/~mgk25/unicode.html>
• How Does Unicode Work With Traditional Locales?
If your locale is a UTF-8 locale, starting in Perl v5.26, Perl works
well for all categories; before this, starting with Perl v5.20, it
works for all categories but "LC_COLLATE", which deals with sorting
and the "cmp" operator. But note that the standard
"Unicode::Collate" and "Unicode::Collate::Locale" modules offer much
more powerful solutions to collation issues, and work on earlier
releases.
For other locales, starting in Perl 5.16, you can specify
use locale ':not_characters';
to get Perl to work well with them. The catch is that you have to
translate from the locale character set to/from Unicode yourself.
See "Unicode I/O" above for how to
use open ':locale';
to accomplish this, but full details are in "Unicode and UTF-8" in
perllocale, including gotchas that happen if you don't specify
":not_characters".
Hexadecimal Notation
The Unicode standard prefers using hexadecimal notation because that
more clearly shows the division of Unicode into blocks of 256
characters. Hexadecimal is also simply shorter than decimal. You can
use decimal notation, too, but learning to use hexadecimal just makes
life easier with the Unicode standard. The "U+HHHH" notation uses
hexadecimal, for example.
The "0x" prefix means a hexadecimal number, the digits are 0-9 and a-f
(or A-F, case doesn't matter). Each hexadecimal digit represents four
bits, or half a byte. "print 0x..., "\n"" will show a hexadecimal
number in decimal, and "printf "%x\n", $decimal" will show a decimal
number in hexadecimal. If you have just the "hex digits" of a
hexadecimal number, you can use the hex() function.
print 0x0009, "\n"; # 9
print 0x000a, "\n"; # 10
print 0x000f, "\n"; # 15
print 0x0010, "\n"; # 16
print 0x0011, "\n"; # 17
print 0x0100, "\n"; # 256
print 0x0041, "\n"; # 65
printf "%x\n", 65; # 41
printf "%#x\n", 65; # 0x41
print hex("41"), "\n"; # 65
Further Resources
• Unicode Consortium
<https://www.unicode.org/>
• Unicode FAQ
<https://www.unicode.org/faq/>
• Unicode Glossary
<https://www.unicode.org/glossary/>
• Unicode Recommended Reading List
The Unicode Consortium has a list of articles and books, some of
which give a much more in depth treatment of Unicode:
<http://unicode.org/resources/readinglist.html>
• Unicode Useful Resources
<https://www.unicode.org/unicode/onlinedat/resources.html>
• Unicode and Multilingual Support in HTML, Fonts, Web Browsers and
Other Applications
<http://www.alanwood.net/unicode/>
• UTF-8 and Unicode FAQ for Unix/Linux
<http://www.cl.cam.ac.uk/~mgk25/unicode.html>
• Legacy Character Sets
<http://www.czyborra.com/> <http://www.eki.ee/letter/>
• You can explore various information from the Unicode data files
using the "Unicode::UCD" module.
UNICODE IN OLDER PERLS
If you cannot upgrade your Perl to 5.8.0 or later, you can still do some
Unicode processing by using the modules "Unicode::String",
"Unicode::Map8", and "Unicode::Map", available from CPAN. If you have
the GNU recode installed, you can also use the Perl front-end
"Convert::Recode" for character conversions.
The following are fast conversions from ISO 8859-1 (Latin-1) bytes to
UTF-8 bytes and back, the code works even with older Perl 5 versions.
# ISO 8859-1 to UTF-8
s/([\x80-\xFF])/chr(0xC0|ord($1)>>6).chr(0x80|ord($1)&0x3F)/eg;
# UTF-8 to ISO 8859-1
s/([\xC2\xC3])([\x80-\xBF])/chr(ord($1)<<6&0xC0|ord($2)&0x3F)/eg;
SEE ALSO
perlunitut, perlunicode, Encode, open, utf8, bytes, perlretut, perlrun,
Unicode::Collate, Unicode::Normalize, Unicode::UCD
ACKNOWLEDGMENTS
Thanks to the kind readers of the perl5-porters@perl.org,
perl-unicode@perl.org, linux-utf8@nl.linux.org, and unicore@unicode.org
mailing lists for their valuable feedback.
AUTHOR, COPYRIGHT, AND LICENSE
Copyright 2001-2011 Jarkko Hietaniemi <jhi@iki.fi>. Now maintained by
Perl 5 Porters.
This document may be distributed under the same terms as Perl itself.
perl v5.40.1 2026-08-30 PERLUNIINTRO(1)
Generated by dwww version 1.16 on Sat Oct 3 07:42:56 CEST 2026.