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
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 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.
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
# 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:
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.
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:
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.