enc2xs -- Perl Encode Module Generator


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


   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

   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

         $ 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

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

             $ 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
         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

       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
     <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>

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

   *   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.

   *   CHARMAP starts the character map section.  Each line has a form as

         <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.

   *   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:

   *   Sort your map in Unicode order.

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

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

     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.


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

   *   ICU Character Mapping Tables

   *   ICU:Conversion Data


   Encode, perlmod, perlpod


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