2011 twenty-four merry days of Perl Feed

A Shortcut to Unicode

utf8::all - 2011-12-21

Unicode is notoriously difficult for programmers to use correctly. Wouldn't it be swell if there were a module you could use to make your program fully Unicode-aware and -correct?

Unfortunately such a thing could never exist, because Unicode is so much more than just English-plus-lots-of-funny-characters. It's a system for handling the writing systems of the thousands of languages in the world. Daunting? You betcha.

There is just too much ambiguity in Perl's builtin functions to transparently upgrade them to be correct in the face of Unicode.


Before you lose all hope, know that there is a module, utf8::all, that can get you most of the way to Unicode nirvana. It was borne out of the perl5i project, quickly spun out as a useful standalone module.

utf8::all sets up the most common channels that your program will use to interact with the outside world to manage the UTF-8 encoding and decoding for you. That means that when you, say, shift off an argument from @ARGV, you will get a character string instead of octets. When you log to STDERR, utf8::all ensures that the characters you warn are encoded to the octets that the outside world expects.

While a full explanation of the difference between characters and octets is beyond the scope of this article, it is important to know that any time you are dealing with text you need to operate on characters. Violate this rule and you're likely to end up with garbage.

Say we have a program that greets the name you pass in.

use 5.14.2;
use warnings;

my $name = join " ", @ARGV;

say "HI " . uc($name) . "!";

Run this with "Santa Claus" and you get "HI SANTA CLAUS!". Great! But once you leave the 26-letter English things get worse quickly. Try the French "Père Noël" and you'll get "HI PèRE NOëL!" Not perfect, but at least it stays readable. Go further afield to the Japanese "サンタクロース" and you'll end up with nothing but mojibake and coal in your stocking.

By adding use utf8::all to this program, @ARGV is decoded from octets into characters and STDOUT is encoded from characters into octets for you. That means the results will end up being "HI SANTA CLAUS!", "HI PÈRE NOËL!", and "HI サンタクロース!" Certainly a lot more respectable.

This module is especially useful for one-liners, since fiddling with the encoding of @ARGV, STDIN, and STDOUT takes a lot more code than simply using an -M on utf8::all. Say we wanted to write a filter that converts its input to Sᴍᴀʟʟᴄᴀᴘs. Note that we have to carefully set up the encoding of not only both STDIN and STDOUT, but also of the program itself. If we forget to tell Perl that our code is written in UTF-8 (by loading the special utf8 module), then our transliteration will produce garbage, because Perl will see the right-hand side of the tr as 64 octets, not 26 characters.

perl -Mutf8 -pe 'BEGIN { binmode($_, ":utf8") for STDIN, STDOUT }

If that looks like a lot to spring from your fingers every time you want to write a one-liner that handles Unicode correctly, it certainly is. That one-liner doesn't even handle STDERR, @ARGV, or any additional file handles we might open!

Instead, by simply declaring -Mutf8::all, you don't have to micromanage any of that.

perl -Mutf8::all -pe 'tr[a-z][ᴀʙᴄᴅᴇꜰɢʜɪᴊᴋʟᴍɴᴏᴘQʀsᴛᴜᴠᴡxʏᴢ]'

Tʜᴇ ꜰᴜᴛᴜʀᴇ ɪs ʜᴇʀᴇ!

utf8::all's reach

utf8::all doesn't cover all of the suggestions Tom Christiansen outlines in his epic Stack Overflow post for basic Unicode support, but it does have open tickets for the features it misses! Right now (as of the upcoming 0.03), it's only missing an automatic unicode_strings and promoting encoding problems to fatal errors.

There are also loads of cases utf8::all will never be able catch. Despite its name, there is simply no sane way to dictate that everything must be Unicode. There is too much existing code out there which will break if you change its basic assumptions. For example if you're using DBD::SQLite, you'll need to explicitly turn on UTF-8 handling like so:

my $dbh = DBI->connect("dbi:SQLite:dbname=$file");
$dbh->{sqlite_unicode} = 1;

There's also nothing this module, or any module really, can do to magically fix your English-specific assumptions. If you perform a text-munging operation like s/[0-9]//g then there's no way to programmatically generalize that to Unicode. There are lots of other ways to write numerals besides the familiar Arabic digits, like Ⅶ, 万, and ៧, so a human with an understanding of the business requirements needs to decide which kinds of numerals to include and which kinds to exclude. There's no way a program can make the right choice for you.

All that said, utf8::all is still a mighty useful tool, especially for one-liners and small scripts, since it gets you 90% of the way there. If you're still reeling from all this, let utf8::all serve as your first toe into the vast ocean of Unicode. It's (nearly) 2012 and the world is growing only more and more interconnected, so you are running out of excuses for not learning about how to deal with encodings.

See Also

Gravatar Image This article contributed by: Shawn M Moore <sartak@gmail.com>