1Text::Unidecode(3) User Contributed Perl Documentation Text::Unidecode(3)
2
6 Text::Unidecode -- US-ASCII transliterations of Unicode text
7
9 use utf8;
10 use Text::Unidecode;
11 print unidecode(
12 "\x{5317}\x{4EB0}\n"
13 # those are the Chinese characters for Beijing
14 );
15 # That prints: Bei Jing
17
19 It often happens that you have non-Roman text data in Unicode, but you
20 can't display it -- usually because you're trying to show it to a user
21 via an application that doesn't support Unicode, or because the fonts
22 you need aren't accessible. You could represent the Unicode characters
23 as "???????" or "\15BA\15A0\1610...", but that's nearly useless to the
24 user who actually wants to read what the text says.
25 What Text::Unidecode provides is a function, "unidecode(...)" that
27 takes Unicode data and tries to represent it in US-ASCII characters
28 (i.e., the universally displayable characters between 0x00 and 0x7F).
29 The representation is almost always an attempt at transliteration --
30 i.e., conveying, in Roman letters, the pronunciation expressed by the
31 text in some other writing system. (See the example in the synopsis.)
32 Unidecode's ability to transliterate is limited by two factors:
34 · The amount and quality of data in the original
36 So if you have Hebrew data that has no vowel points in it, then
38 Unidecode cannot guess what vowels should appear in a
39 pronounciation. S f y hv n vwls n th npt, y wn't gt ny vwls n th
40 tpt. (This is a specific application of the general principle of
41 "Garbage In, Garbage Out".)
42 · Basic limitations in the Unidecode design
44 Writing a real and clever transliteration algorithm for any single
46 language usually requires a lot of time, and at least a passable
47 knowledge of the language involved. But Unicode text can convey
48 more languages than I could possibly learn (much less create a
49 transliterator for) in the entire rest of my lifetime. So I put a
50 cap on how intelligent Unidecode could be, by insisting that it
51 support only context-insensitive transliteration. That means
52 missing the finer details of any given writing system, while still
53 hopefully being useful.
54 Unidecode, in other words, is quick and dirty. Sometimes the output is
56 not so dirty at all: Russian and Greek seem to work passably; and while
57 Thaana (Divehi, AKA Maldivian) is a definitely non-Western writing
58 system, setting up a mapping from it to Roman letters seems to work
59 pretty well. But sometimes the output is very dirty: Unidecode does
60 quite badly on Japanese and Thai.
61 If you want a smarter transliteration for a particular language than
63 Unidecode provides, then you should look for (or write) a
64 transliteration algorithm specific to that language, and apply it
65 instead of (or at least before) applying Unidecode.
66 In other words, Unidecode's approach is broad (knowing about dozens of
68 writing systems), but shallow (not being meticulous about any of them).
69
71 Text::Unidecode provides one function, "unidecode(...)", which is
72 exported by default. It can be used in a variety of calling contexts:
73 "$out = unidecode($in);" # scalar context
75 This returns a copy of $in, transliterated.
76 "$out = unidecode(@in);" # scalar context
78 This is the same as "$out = unidecode(join '', @in);"
79 "@out = unidecode(@in);" # list context
81 This returns a list consisting of copies of @in, each
82 transliterated. This is the same as "@out = map
83 scalar(unidecode($_)), @in;"
84 "unidecode(@items);" # void context
86 "unidecode(@bar, $foo, @baz);" # void context
87 Each item on input is replaced with its transliteration. This is
88 the same as "for(@bar, $foo, @baz) { $_ = unidecode($_) }"
89 You should make a minimum of assumptions about the output of
91 "unidecode(...)". For example, if you assume an all-alphabetic
92 (Unicode) string passed to "unidecode(...)" will return an all-
93 alphabetic string, you're wrong -- some alphabetic Unicode characters
94 are transliterated as strings containing punctuation (e.g., the
95 Armenian letter at 0x0539 currently transliterates as "T`".
96 However, these are the assumptions you can make:
98 · Each character 0x0000 - 0x007F transliterates as itself. That is,
100 "unidecode(...)" is 7-bit pure.
101 · The output of "unidecode(...)" always consists entirely of US-ASCII
103 characters -- i.e., characters 0x0000 - 0x007F.
104 · All Unicode characters translate to a sequence of (any number of)
106 characters that are newline ("\n") or in the range 0x0020-0x007E.
107 That is, no Unicode character translates to "\x01", for example.
108 (Altho if you have a "\x01" on input, you'll get a "\x01" in
109 output.)
110 · Yes, some transliterations produce a "\n" -- but just a few, and
112 only with good reason. Note that the value of newline ("\n")
113 varies from platform to platform -- see "perlport" in perlport.
114 · Some Unicode characters may transliterate to nothing (i.e., empty
116 string).
117 · Very many Unicode characters transliterate to multi-character
119 sequences. E.g., Han character 0x5317 transliterates as the four-
120 character string "Bei ".
121 · Within these constraints, I may change the transliteration of
123 characters in future versions. For example, if someone convinces
124 me that the Armenian letter at 0x0539, currently transliterated as
125 "T`", would be better transliterated as "D", I may well make that
126 change.
127
129 Text::Unidecode is meant to be a transliterator-of-last resort, to be
130 used once you've decided that you can't just display the Unicode data
131 as is, and once you've decided you don't have a more clever, language-
132 specific transliterator available. It transliterates context-
133 insensitively -- that is, a given character is replaced with the same
134 US-ASCII (7-bit ASCII) character or characters, no matter what the
135 surrounding character are.
136 The main reason I'm making Text::Unidecode work with only context-
138 insensitive substitution is that it's fast, dumb, and straightforward
139 enough to be feasable. It doesn't tax my (quite limited) knowledge of
140 world languages. It doesn't require me writing a hundred lines of code
141 to get the Thai syllabification right (and never knowing whether I've
142 gotten it wrong, because I don't know Thai), or spending a year trying
143 to get Text::Unidecode to use the ChaSen algorithm for Japanese, or
144 trying to write heuristics for telling the difference between Japanese,
145 Chinese, or Korean, so it knows how to transliterate any given Uni-Han
146 glyph. And moreover, context-insensitive substitution is still mostly
147 useful, but still clearly couldn't be mistaken for authoritative.
148 Text::Unidecode is an example of the 80/20 rule in action -- you get
150 80% of the usefulness using just 20% of a "real" solution.
151 A "real" approach to transliteration for any given language can involve
153 such increasingly tricky contextual factors as these
154 The previous / preceding character(s)
156 What a given symbol "X" means, could depend on whether it's
157 followed by a consonant, or by vowel, or by some diacritic
158 character.
159 Syllables
161 A character "X" at end of a syllable could mean something different
162 from when it's at the start -- which is especially problematic when
163 the language involved doesn't explicitly mark where one syllable
164 stops and the next starts.
165 Parts of speech
167 What "X" sounds like at the end of a word, depends on whether that
168 word is a noun, or a verb, or what.
169 Meaning
171 By semantic context, you can tell that this ideogram "X" means
172 "shoe" (pronounced one way) and not "time" (pronounced another),
173 and that's how you know to transliterate it one way instead of the
174 other.
175 Origin of the word
177 "X" means one thing in loanwords and/or placenames (and derivatives
178 thereof), and another in native words.
179 "It's just that way"
181 "X" normally makes the /X/ sound, except for this list of seventy
182 exceptions (and words based on them, sometimes indirectly). Or:
183 you never can tell which of the three ways to pronounce "X" this
184 word actually uses; you just have to know which it is, so keep a
185 dictionary on hand!
186 Language
188 The character "X" is actually used in several different languages,
189 and you have to figure out which you're looking at before you can
190 determine how to transliterate it.
191 Out of a desire to avoid being mired in any of these kinds of
193 contextual factors, I chose to exclude all of them and just stick with
194 context-insensitive replacement.
195
197 Things that need tending to are detailed in the TODO.txt file, included
198 in this distribution. Normal installs probably don't leave the
199 TODO.txt lying around, but if nothing else, you can see it at
200 http://search.cpan.org/search?dist=Text::Unidecode
201
203 The Text::Unidecode motto is:
204 It's better than nothing!
206 ...in both meanings: 1) seeing the output of "unidecode(...)" is better
208 than just having all font-unavailable Unicode characters replaced with
209 "?"'s, or rendered as gibberish; and 2) it's the worst, i.e., there's
210 nothing that Text::Unidecode's algorithm is better than.
211
213 If you get really implausible nonsense out of "unidecode(...)", make
214 sure that the input data really is a utf8 string. See "perlunicode" in
215 perlunicode.
216
218 Thanks to Harald Tveit Alvestrand, Abhijit Menon-Sen, and Mark-Jason
219 Dominus.
220
222 Unicode Consortium: http://www.unicode.org/
223 Geoffrey Sampson. 1990. Writing Systems: A Linguistic Introduction.
225 ISBN: 0804717567
226 Randall K. Barry (editor). 1997. ALA-LC Romanization Tables:
228 Transliteration Schemes for Non-Roman Scripts. ISBN: 0844409405 [ALA
229 is the American Library Association; LC is the Library of Congress.]
230 Rupert Snell. 2000. Beginner's Hindi Script (Teach Yourself Books).
232 ISBN: 0658009109
233
235 Copyright (c) 2001 Sean M. Burke. All rights reserved.
236 This library is free software; you can redistribute it and/or modify it
238 under the same terms as Perl itself.
239 This program is distributed in the hope that it will be useful, but
241 without any warranty; without even the implied warranty of
242 merchantability or fitness for a particular purpose.
243 Much of Text::Unidecode's internal data is based on data from The
245 Unicode Consortium, with which I am unafiliated.
246
248 Sean M. Burke "sburke@cpan.org"
249perl v5.16.3 2001-07-14 Text::Unidecode(3)