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

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

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

NNAAMMEE #

 enc2xs -- Perl Encode Module Generator

SSYYNNOOPPSSIISS #

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

DDEESSCCRRIIPPTTIIOONN #

 _e_n_c_2_x_s 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 _e_n_c_2_x_s to add your own encoding to perl.  No knowledge of XS is
 necessary.

QQuuiicckk GGuuiiddee 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 _m_y_._u_c_m.  "$" 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 (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

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

TThhee UUnniiccooddee CChhaarraacctteerr MMaapp 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 #

 •   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 _<_k_e_y_w_o_r_d_> _v_a_l_u_e, one pair per
     line.  Strings used as values must be quoted. Barewords are treated
     as numbers.  _\_x_X_X represents a byte.

     Most of the keywords are self-explanatory. _s_u_b_c_h_a_r 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
     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.

 •   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 UU00000000 to UU00002200 as is, unless
 your environment is EBCDIC.

 CCAAVVEEAATT: 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.

CCooppiinngg wwiitthh dduupplliiccaattee mmaappppiinnggss 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
 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 _u_c_m_l_i_n_t, 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 _u_c_m_s_o_r_t, yet another utility under Encode/bin
 directory.

BBooookkmmaarrkkss • ICU Home Page http://www.icu-project.org/

 •   ICU Character Mapping Tables
     <http://site.icu-project.org/charts/charset>

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

SSEEEE AALLSSOO #

 Encode, perlmod, perlpod

perl v5.36.3 2024-03-20 ENC2XS(1)