


ENC2XS(1)        Perl Programmers Reference Guide       ENC2XS(1)


NAME
       enc2xs -- Perl Encode Module Generator

SYNOPSIS
         enc2xs -[options]
         enc2xs -M ModName mapfiles...
         enc2xs -C

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

Quick Guide
       If you want to know as little about Perl as possible but
       need to add a new encoding, just read this chapter and
       forget the rest.

       0.  Have a .ucm file ready.  You can get it from somewhere
           or you can write your own from scratch or you can grab
           one from the Encode distribution and customize it.
           For the UCM format, see the next Chapter.  In the
           example below, I'll call my theoretical encoding
           myascii, defined in my.ucm.  "$" is a shell prompt.

             $ ls -F
             my.ucm

       1.  Issue a command as follows;

             $ enc2xs -M My my.ucm
             generating Makefile.PL
             generating My.pm
             generating README
             generating Changes

           Now take a look at your current directory.  It should
           look like this.

             $ ls -F
             Makefile.PL   My.pm         my.ucm        t/

           The following files were created.

             Makefile.PL - MakeMaker script
             My.pm       - Encode submodule
             t/My.t      - test file

           1.1.
               If you want *.ucm installed together with the
               modules, do as follows;



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                 $ mkdir Encode
                 $ mv *.ucm Encode
                 $ enc2xs -M My Encode/*ucm

       2.  Edit the files generated.  You don't have to if you
           have no time AND no intention to give it to someone
           else.  But it is a good idea to edit the pod and to
           add more tests.

       3.  Now issue a command all Perl Mongers love:

             $ perl Makefile.PL
             Writing Makefile for Encode::My

       4.  Now all you have to do is make.

             $ make
             cp My.pm blib/lib/Encode/My.pm
             /usr/local/bin/perl /usr/local/bin/enc2xs -Q -O \
               -o encode_t.c -f encode_t.fnm
             Reading myascii (myascii)
             Writing compiled form
             128 bytes in string tables
             384 bytes (75%) saved spotting duplicates
             1 bytes (0.775%) saved using substrings
             ....
             chmod 644 blib/arch/auto/Encode/My/My.bs
             $

           The time it takes varies depending on how fast your
           machine is and how large your encoding is.  Unless you
           are working on something big like euc-tw, it won't
           take too long.

       5.  You can "make install" already but you should test
           first.

             $ make test
             PERL_DL_NONLAZY=1 /usr/local/bin/perl -Iblib/arch -Iblib/lib \
               -e 'use Test::Harness  qw(&runtests $verbose); \
               $verbose=0; runtests @ARGV;' t/*.t
             t/My....ok
             All tests successful.
             Files=1, Tests=2,  0 wallclock secs
              ( 0.09 cusr + 0.01 csys = 0.09 CPU)

       6.  If you are content with the test result, just "make
           install"

       7.  If you want to add your encoding to Encode's demand-
           loading list (so you don't have to "use
           Encode::YourEncoding"), run

             enc2xs -C



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           to update Encode::ConfigLocal, a module that controls
           local settings.  After that, "use Encode;" is enough
           to load your encodings on demand.

The Unicode Character Map
       Encode uses the Unicode Character Map (UCM) format for
       source character mappings.  This format is used by IBM's
       ICU package and was adopted by Nick Ing-Simmons for use
       with the Encode module.  Since UCM is more flexible than
       Tcl's Encoding Map and far more user-friendly, this is the
       recommended format for Encode now.

       A UCM file looks like this.

         #
         # Comments
         #
         <code_set_name> "US-ascii" # Required
         <code_set_alias> "ascii"   # Optional
         <mb_cur_min> 1             # Required; usually 1
         <mb_cur_max> 1             # Max. # of bytes/char
         <subchar> \x3F             # Substitution char
         #
         CHARMAP
         <U0000> \x00 |0 # <control>
         <U0001> \x01 |0 # <control>
         <U0002> \x02 |0 # <control>
         ....
         <U007C> \x7C |0 # VERTICAL LINE
         <U007D> \x7D |0 # RIGHT CURLY BRACKET
         <U007E> \x7E |0 # TILDE
         <U007F> \x7F |0 # <control>
         END CHARMAP

       o   Anything that follows "#" is treated as a comment.

       o   The header section continues until a line containing
           the word CHARMAP. This section has a form of <keyword>
           value, one pair per line.  Strings used as values must
           be quoted. Barewords are treated as numbers.  \xXX
           represents a byte.

           Most of the keywords are self-explanatory. subchar
           means substitution character, not subcharacter.  When
           you decode a Unicode sequence to this encoding but no
           matching character is found, the byte sequence defined
           here will be used.  For most cases, the value here is
           \x3F; in ASCII, this is a question mark.

       o   CHARMAP starts the character map section.  Each line
           has a form as follows:






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             <UXXXX> \xXX.. |0 # comment
               ^     ^      ^
               |     |      +- Fallback flag
               |     +-------- Encoded byte sequence
               +-------------- Unicode Character ID in hex

           The format is roughly the same as a header section
           except for the fallback flag: | followed by 0..3.
           The meaning of the possible values is as follows:

           |0  Round trip safe.  A character decoded to Unicode
               encodes back to the same byte sequence.  Most
               characters have this flag.

           |1  Fallback for unicode -> encoding.  When seen,
               enc2xs adds this character for the encode map
               only.

           |2  Skip sub-char mapping should there be no code
               point.

           |3  Fallback for encoding -> unicode.  When seen,
               enc2xs adds this character for the decode map
               only.

       o   And finally, END OF CHARMAP ends the section.

       When you are manually creating a UCM file, you should copy
       ascii.ucm or an existing encoding which is close to yours,
       rather than write your own from scratch.

       When you do so, make sure you leave at least U0000 to
       U0020 as is, unless your environment is EBCDIC.

       CAVEAT: not all features in UCM are implemented.  For
       example, icu:state is not used.  Because of that, you need
       to write a perl module if you want to support
       algorithmical encodings, notably the ISO-2022 series.
       Such modules include Encode::JP::2022_JP,
       Encode::KR::2022_KR, and Encode::TW::HZ.

   Coping with duplicate mappings
       When you create a map, you SHOULD make your mappings
       round-trip safe.  That is, "encode('your-encoding',
       decode('your-encoding', $data)) eq $data" stands for all
       characters that are marked as "|0".  Here is how to make
       sure:

       o   Sort your map in Unicode order.

       o   When you have a duplicate entry, mark either one with
           '|1' or '|3'.

       o   And make sure the '|1' or '|3' entry FOLLOWS the '|0'



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           entry.

       Here is an example from big5-eten.

         <U2550> \xF9\xF9 |0
         <U2550> \xA2\xA4 |3

       Internally Encoding -> Unicode and Unicode -> Encoding Map
       looks like this;

         E to U               U to E
         --------------------------------------
         \xF9\xF9 => U2550    U2550 => \xF9\xF9
         \xA2\xA4 => U2550

       So it is round-trip safe for \xF9\xF9.  But if the line
       above is upside down, here is what happens.

         E to U               U to E
         --------------------------------------
         \xA2\xA4 => U2550    U2550 => \xF9\xF9
         (\xF9\xF9 => U2550 is now overwritten!)

       The Encode package comes with ucmlint, a crude but
       sufficient utility to check the integrity of a UCM file.
       Check under the Encode/bin directory for this.

       When in doubt, you can use ucmsort, yet another utility
       under Encode/bin directory.

Bookmarks
       o   ICU Home Page <http://www.icu-project.org/>

       o   ICU Character Mapping Tables
           <http://www.icu-project.org/charset/>

       o   ICU:Conversion Data
           <http://www.icu-project.org/userguide/conversion-data.html>

SEE ALSO
       Encode, perlmod, perlpod
















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