NAME
Text::Unidecode - US-ASCII transliterations of Unicode text
VERSION
version 0.05
SYNOPSIS
use utf8;
use Text::Unidecode;
print unidecode("\x{5317}\x{4EB0}\n"); # Those are the Chinese characters for Beijing
# Prints 'Bei Jing'
DESCRIPTION
It often happens that you have non-Roman text data in Unicode, but you
can't display it -- usually because you're trying to show it to a user
via an application that doesn't support Unicode, or because the fonts
you need aren't accessible. You could represent the Unicode characters
as "???????" or "\15BA\15A0\1610...", but that's nearly useless to the
user who actually wants to read what the text says.
What Text::Unidecode provides is a function, "unidecode(...)" that takes
Unicode data and tries to represent it in US-ASCII characters (i.e., the
universally displayable characters between 0x00 and 0x7F). The
representation is almost always an attempt at *transliteration* -- i.e.,
conveying, in Roman letters, the pronunciation expressed by the text in
some other writing system. (See the example in the synopsis.)
Text::Unidecode's ability to transliterate is limited by two factors:
* The amount and quality of data in the original
So if you have Hebrew data that has no vowel points in it, then
Unidecode cannot guess what vowels should appear in a
pronounciation. S f y hv n vwls n th npt, y wn't gt ny vwls n th
tpt. (This is a specific application of the general principle of
"Garbage In, Garbage Out".)
* Basic limitations in the Unidecode design
Writing a real and clever transliteration algorithm for any single
language usually requires a lot of time, and at least a passable
knowledge of the language involved. But Unicode text can convey more
languages than I could possibly learn (much less create a
transliterator for) in the entire rest of my lifetime. So I put a
cap on how intelligent Unidecode could be, by insisting that it
support only context-*in*sensitive transliteration. That means
missing the finer details of any given writing system, while still
hopefully being useful.
Unidecode, in other words, is quick and dirty. Sometimes the output is
not so dirty at all: Russian and Greek seem to work passably; and while
Thaana (Divehi, AKA Maldivian) is a definitely non-Western writing
system, setting up a mapping from it to Roman letters seems to work
pretty well. But sometimes the output is *very dirty*: Unidecode does
quite badly on Japanese and Thai.
If you want a smarter transliteration for a particular language than
Unidecode provides, then you should look for (or write) a
transliteration algorithm specific to that language, and apply it
instead of (or at least before) applying Unidecode.
In other words, Unidecode's approach is broad (knowing about dozens of
writing systems), but shallow (not being meticulous about any of them).
FUNCTIONS
Text::Unidecode provides one function, "unidecode()", which is exported
by default.
unidecode
"unidecode()" can be used in a variety of calling contexts:
"$out = unidecode($in);" # scalar context
This returns a copy of $in, transliterated.
"$out = unidecode(@in);" # scalar context
This is the same as "$out = unidecode(join '', @in);"
"@out = unidecode(@in);" # list context
This returns a list consisting of copies of @in, each
transliterated. This is the same as "@out = map
scalar(unidecode($_)), @in;"
"unidecode(@items);" # void context
"unidecode(@bar, $foo, @baz);" # void context
Each item on input is replaced with its transliteration. This is the
same as "for(@bar, $foo, @baz) { $_ = unidecode($_) }"
You should make a minimum of assumptions about the output of
"unidecode(...)". For example, if you assume an all-alphabetic (Unicode)
string passed to "unidecode(...)" will return an all-alphabetic string,
you're wrong -- some alphabetic Unicode characters are transliterated as
strings containing punctuation (e.g., the Armenian letter at 0x0539
currently transliterates as "T`".
However, these are the assumptions you *can* make:
* Each character 0x0000 - 0x007F transliterates as itself. That is,
"unidecode(...)" is 7-bit pure.
* The output of "unidecode(...)" always consists entirely of US-ASCII
characters -- i.e., characters 0x0000 - 0x007F.
* All Unicode characters translate to a sequence of (any number of)
characters that are newline ("\n") or in the range 0x0020-0x007E.
That is, no Unicode character translates to "\x01", for example.
(Although if you have a "\x01" in input, you'll get a "\x01" in
output.)
* Yes, some transliterations produce a "\n" -- but just a few, and
only with good reason. Note that the value of newline ("\n") varies
from platform to platform -- see perlport.
* Some Unicode characters may transliterate to nothing (i.e., empty
string).
* Very many Unicode characters transliterate to multi-character
sequences. E.g., Han character 0x5317 transliterates as the
four-character string "Bei ".
* Within these constraints, I may change the transliteration of
characters in future versions. For example, if someone convinces me
that the Armenian letter at 0x0539, currently transliterated as
"T`", would be better transliterated as "D", I may well make that
change.
remap
This remaps a transliteration temporarily. Give it one character, and
the desired transliteration:
my %remap = (
'A' => 'omg',
'B' => 'really?!',
);
while (my ($char, $remap) = each %remap) {
remap($char, $remap);
}
print unidecode('ABCDE'); # see your alternate transliterations
unidecode_to_charset
This attempts to "unidecode()" to any arbitrary charset, rather than to
US-ASCII. The function is not exported by default.
Pass the target charset as the first parameter (default is ascii), and
the text to transliterate as the second.
DESIGN GOALS AND CONSTRAINTS
Text::Unidecode is meant to be a transliterator-of-last resort, to be
used once you've decided that you can't just display the Unicode data as
is, and once you've decided you don't have a more clever,
language-specific transliterator available. It transliterates
context-insensitively -- that is, a given character is replaced with the
same US-ASCII (7-bit ASCII) character or characters, no matter what the
surrounding character are.
The main reason I'm making Text::Unidecode work with only
context-insensitive substitution is that it's fast, dumb, and
straightforward enough to be feasable. It doesn't tax my (quite limited)
knowledge of world languages. It doesn't require me writing a hundred
lines of code to get the Thai syllabification right (and never knowing
whether I've gotten it wrong, because I don't know Thai), or spending a
year trying to get Text::Unidecode to use the ChaSen algorithm for
Japanese, or trying to write heuristics for telling the difference
between Japanese, Chinese, or Korean, so it knows how to transliterate
any given Uni-Han glyph. And moreover, context-insensitive substitution
is still mostly useful, but still clearly couldn't be mistaken for
authoritative.
Text::Unidecode is an example of the 80/20 rule in action -- you get 80%
of the usefulness using just 20% of a "real" solution.
A "real" approach to transliteration for any given language can involve
such increasingly tricky contextual factors as these
The previous / preceding character(s)
What a given symbol "X" means, could depend on whether it's followed
by a consonant, or by vowel, or by some diacritic character.
Syllables
A character "X" at end of a syllable could mean something different
from when it's at the start -- which is especially problematic when
the language involved doesn't explicitly mark where one syllable
stops and the next starts.
Parts of speech
What "X" sounds like at the end of a word, depends on whether that
word is a noun, or a verb, or what.
Meaning
By semantic context, you can tell that this ideogram "X" means
"shoe" (pronounced one way) and not "time" (pronounced another), and
that's how you know to transliterate it one way instead of the
other.
Origin of the word
"X" means one thing in loanwords and/or placenames (and derivatives
thereof), and another in native words.
"It's just that way"
"X" normally makes the /X/ sound, except for this list of seventy
exceptions (and words based on them, sometimes indirectly). Or: you
never can tell which of the three ways to pronounce "X" this word
actually uses; you just have to know which it is, so keep a
dictionary on hand!
Language
The character "X" is actually used in several different languages,
and you have to figure out which you're looking at before you can
determine how to transliterate it.
Out of a desire to avoid being mired in *any* of these kinds of
contextual factors, I chose to exclude *all of them* and just stick with
context-insensitive replacement.
MOTTO
The Text::Unidecode motto is:
It's better than nothing!
...in both meanings: 1) seeing the output of "unidecode(...)" is better
than just having all font-unavailable Unicode characters replaced with
"?"'s, or rendered as gibberish; and 2) it's the worst, i.e., there's
nothing that Text::Unidecode's algorithm is better than.
CAVEATS
If you get really implausible nonsense out of "unidecode(...)", make
sure that the input data really is a utf8 string. See perlunicode.
THANKS
Thanks to Harald Tveit Alvestrand, Abhijit Menon-Sen, and Mark-Jason
Dominus.
SEE ALSO
* Unicode Consortium: <http://www.unicode.org>
* Geoffrey Sampson. 1990. *Writing Systems: A Linguistic
Introduction.* ISBN: 0804717567
* Randall K. Barry (editor). 1997. *ALA-LC Romanization Tables:
Transliteration Schemes for Non-Roman Scripts.* ISBN: 0844409405
[ALA is the American Library Association; LC is the Library of
Congress.]
* Rupert Snell. 2000. *Beginner's Hindi Script (Teach Yourself
Books).* ISBN: 0658009109
AVAILABILITY
The latest version of this module is available from the Comprehensive
Perl Archive Network (CPAN). Visit <http://www.perl.com/CPAN/> to find a
CPAN site near you, or see
<http://search.cpan.org/dist/Text-Unidecode/>.
The development version lives at
<http://github.com/doherty/Text-Unidecode> and may be cloned from
<git://github.com/doherty/Text-Unidecode.git>. Instead of sending
patches, please fork this project using the standard git and github
infrastructure.
SOURCE
The development version is on github at
<http://github.com/doherty/Text-Unidecode> and may be cloned from
<git://github.com/doherty/Text-Unidecode.git>
BUGS AND LIMITATIONS
No bugs have been reported.
Please report any bugs or feature requests through the web interface at
<http://github.com/doherty/Text-Unidecode/issues>.
AUTHOR
Sean M. Burke <sburke@cpan.org>
COPYRIGHT AND LICENSE
This software is copyright (c) 2001 by Sean M. Burke.
This is free software; you can redistribute it and/or modify it under
the same terms as the Perl 5 programming language system itself.