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;

   $ 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 (25%) saved spotting duplicates
    1 bytes (99.2%) 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

   to update Encode::ConfigLocal, a module that controls local set-
   tings. 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 formet 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 substitu-
   tion 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:

    <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 mod-
    ule 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' 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.

Bookmarks
    o  ICU Home Page <http://oss.software.ibm.com/icu/>

    o  ICU Character Mapping Tables <http://oss.soft-
   ware.ibm.com/icu/charset/>

    o  ICU:Conversion Data <http://oss.software.ibm.com/icu/userguide/con-
   version-data.html>

SEE ALSO
    Encode, perlmod, perlpod