1ENC2XS(1)             User Contributed Perl Documentation            ENC2XS(1)
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NAME

6       enc2xs -- Perl Encode Module Generator
7

SYNOPSIS

9         enc2xs -[options]
10         enc2xs -M ModName mapfiles...
11         enc2xs -C
12

DESCRIPTION

14       enc2xs builds a Perl extension for use by Encode from either Unicode
15       Character Mapping files (.ucm) or Tcl Encoding Files (.enc).  Besides
16       being used internally during the build process of the Encode module,
17       you can use enc2xs to add your own encoding to perl.  No knowledge of
18       XS is necessary.
19

Quick Guide

21       If you want to know as little about Perl as possible but need to add a
22       new encoding, just read this chapter and forget the rest.
23
24       0.  Have a .ucm file ready.  You can get it from somewhere or you can
25           write your own from scratch or you can grab one from the Encode
26           distribution and customize it.  For the UCM format, see the next
27           Chapter.  In the example below, I'll call my theoretical encoding
28           myascii, defined in my.ucm.  "$" is a shell prompt.
29
30             $ ls -F
31             my.ucm
32
33       1.  Issue a command as follows;
34
35             $ enc2xs -M My my.ucm
36             generating Makefile.PL
37             generating My.pm
38             generating README
39             generating Changes
40
41           Now take a look at your current directory.  It should look like
42           this.
43
44             $ ls -F
45             Makefile.PL   My.pm         my.ucm        t/
46
47           The following files were created.
48
49             Makefile.PL - MakeMaker script
50             My.pm       - Encode submodule
51             t/My.t      - test file
52
53           1.1.
54               If you want *.ucm installed together with the modules, do as
55               follows;
56
57                 $ mkdir Encode
58                 $ mv *.ucm Encode
59                 $ enc2xs -M My Encode/*ucm
60
61       2.  Edit the files generated.  You don't have to if you have no time
62           AND no intention to give it to someone else.  But it is a good idea
63           to edit the pod and to add more tests.
64
65       3.  Now issue a command all Perl Mongers love:
66
67             $ perl Makefile.PL
68             Writing Makefile for Encode::My
69
70       4.  Now all you have to do is make.
71
72             $ make
73             cp My.pm blib/lib/Encode/My.pm
74             /usr/local/bin/perl /usr/local/bin/enc2xs -Q -O \
75               -o encode_t.c -f encode_t.fnm
76             Reading myascii (myascii)
77             Writing compiled form
78             128 bytes in string tables
79             384 bytes (75%) saved spotting duplicates
80             1 bytes (0.775%) saved using substrings
81             ....
82             chmod 644 blib/arch/auto/Encode/My/My.bs
83             $
84
85           The time it takes varies depending on how fast your machine is and
86           how large your encoding is.  Unless you are working on something
87           big like euc-tw, it won't take too long.
88
89       5.  You can "make install" already but you should test first.
90
91             $ make test
92             PERL_DL_NONLAZY=1 /usr/local/bin/perl -Iblib/arch -Iblib/lib \
93               -e 'use Test::Harness  qw(&runtests $verbose); \
94               $verbose=0; runtests @ARGV;' t/*.t
95             t/My....ok
96             All tests successful.
97             Files=1, Tests=2,  0 wallclock secs
98              ( 0.09 cusr + 0.01 csys = 0.09 CPU)
99
100       6.  If you are content with the test result, just "make install"
101
102       7.  If you want to add your encoding to Encode's demand-loading list
103           (so you don't have to "use Encode::YourEncoding"), run
104
105             enc2xs -C
106
107           to update Encode::ConfigLocal, a module that controls local
108           settings.  After that, "use Encode;" is enough to load your
109           encodings on demand.
110

The Unicode Character Map

112       Encode uses the Unicode Character Map (UCM) format for source character
113       mappings.  This format is used by IBM's ICU package and was adopted by
114       Nick Ing-Simmons for use with the Encode module.  Since UCM is more
115       flexible than Tcl's Encoding Map and far more user-friendly, this is
116       the recommended format for Encode now.
117
118       A UCM file looks like this.
119
120         #
121         # Comments
122         #
123         <code_set_name> "US-ascii" # Required
124         <code_set_alias> "ascii"   # Optional
125         <mb_cur_min> 1             # Required; usually 1
126         <mb_cur_max> 1             # Max. # of bytes/char
127         <subchar> \x3F             # Substitution char
128         #
129         CHARMAP
130         <U0000> \x00 |0 # <control>
131         <U0001> \x01 |0 # <control>
132         <U0002> \x02 |0 # <control>
133         ....
134         <U007C> \x7C |0 # VERTICAL LINE
135         <U007D> \x7D |0 # RIGHT CURLY BRACKET
136         <U007E> \x7E |0 # TILDE
137         <U007F> \x7F |0 # <control>
138         END CHARMAP
139
140       •   Anything that follows "#" is treated as a comment.
141
142       •   The header section continues until a line containing the word
143           CHARMAP. This section has a form of <keyword> value, one pair per
144           line.  Strings used as values must be quoted. Barewords are treated
145           as numbers.  \xXX represents a byte.
146
147           Most of the keywords are self-explanatory. subchar means
148           substitution character, not subcharacter.  When you decode a
149           Unicode sequence to this encoding but no matching character is
150           found, the byte sequence defined here will be used.  For most
151           cases, the value here is \x3F; in ASCII, this is a question mark.
152
153       •   CHARMAP starts the character map section.  Each line has a form as
154           follows:
155
156             <UXXXX> \xXX.. |0 # comment
157               ^     ^      ^
158               |     |      +- Fallback flag
159               |     +-------- Encoded byte sequence
160               +-------------- Unicode Character ID in hex
161
162           The format is roughly the same as a header section except for the
163           fallback flag: | followed by 0..3.   The meaning of the possible
164           values is as follows:
165
166           |0  Round trip safe.  A character decoded to Unicode encodes back
167               to the same byte sequence.  Most characters have this flag.
168
169           |1  Fallback for unicode -> encoding.  When seen, enc2xs adds this
170               character for the encode map only.
171
172           |2  Skip sub-char mapping should there be no code point.
173
174           |3  Fallback for encoding -> unicode.  When seen, enc2xs adds this
175               character for the decode map only.
176
177       •   And finally, END OF CHARMAP ends the section.
178
179       When you are manually creating a UCM file, you should copy ascii.ucm or
180       an existing encoding which is close to yours, rather than write your
181       own from scratch.
182
183       When you do so, make sure you leave at least U0000 to U0020 as is,
184       unless your environment is EBCDIC.
185
186       CAVEAT: not all features in UCM are implemented.  For example,
187       icu:state is not used.  Because of that, you need to write a perl
188       module if you want to support algorithmical encodings, notably the
189       ISO-2022 series.  Such modules include Encode::JP::2022_JP,
190       Encode::KR::2022_KR, and Encode::TW::HZ.
191
192   Coping with duplicate mappings
193       When you create a map, you SHOULD make your mappings round-trip safe.
194       That is, encode('your-encoding', decode('your-encoding', $data)) eq
195       $data stands for all characters that are marked as "|0".  Here is how
196       to make sure:
197
198       •   Sort your map in Unicode order.
199
200       •   When you have a duplicate entry, mark either one with '|1' or '|3'.
201
202       •   And make sure the '|1' or '|3' entry FOLLOWS the '|0' entry.
203
204       Here is an example from big5-eten.
205
206         <U2550> \xF9\xF9 |0
207         <U2550> \xA2\xA4 |3
208
209       Internally Encoding -> Unicode and Unicode -> Encoding Map looks like
210       this;
211
212         E to U               U to E
213         --------------------------------------
214         \xF9\xF9 => U2550    U2550 => \xF9\xF9
215         \xA2\xA4 => U2550
216
217       So it is round-trip safe for \xF9\xF9.  But if the line above is upside
218       down, here is what happens.
219
220         E to U               U to E
221         --------------------------------------
222         \xA2\xA4 => U2550    U2550 => \xF9\xF9
223         (\xF9\xF9 => U2550 is now overwritten!)
224
225       The Encode package comes with ucmlint, a crude but sufficient utility
226       to check the integrity of a UCM file.  Check under the Encode/bin
227       directory for this.
228
229       When in doubt, you can use ucmsort, yet another utility under
230       Encode/bin directory.
231

Bookmarks

233       •   ICU Home Page <http://www.icu-project.org/>
234
235       •   ICU Character Mapping Tables
236           <http://site.icu-project.org/charts/charset>
237
238       •   ICU:Conversion Data
239           <http://www.icu-project.org/userguide/conversion-data.html>
240

SEE ALSO

242       Encode, perlmod, perlpod
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246perl v5.38.0                      2023-07-20                         ENC2XS(1)
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