|ENC2XS(1)||Perl Programmers Reference Guide||ENC2XS(1)|
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.
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.
- 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
- 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
- If you want *.ucm installed together with the modules, do as follows;
$ mkdir Encode $ mv *.ucm Encode $ enc2xs -M My Encode/*ucm
- 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.
- Now issue a command all Perl Mongers love:
$ perl Makefile.PL Writing Makefile for Encode::My
- 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.
- 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)
- If you are content with the test result, just "make install"
- If you want to add your encoding to Encode's demand-loading list (so you
don't have to "use Encode::YourEncoding"), run
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
- 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 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:
- Round trip safe. A character decoded to Unicode encodes back to the same byte sequence. Most characters have this flag.
- Fallback for unicode -> encoding. When seen, enc2xs adds this character for the encode map only.
- Skip sub-char mapping should there be no code point.
- 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 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.
- 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>
Encode, perlmod, perlpod