Perl has an abstracted interface for all supported character encodings, so this is actually a generic "Encode" tutorial and "Encode" FAQ. But many people think that Unicode is special and magical, and I didn't want to disappoint them, so I decided to call the document a Unicode tutorial.
perl -MEncode -le "print for Encode->encodings(':all')"
You should also check your modules, and upgrade them if necessary. For example, HTML::Entities requires version >= 1.32 to function correctly, even though the changelog is silent about this.
Be careful, though, to never combine text strings with binary strings. If you need text in a binary stream, encode your text strings first using the appropriate encoding, then join them with binary strings. See also: ``What if I don't encode?''.
This silent implicit decoding is known as ``upgrading''. That may sound positive, but it's best to avoid it.
Wide character in print at example.pl line 2.
Because the internal format is often UTF-8, these bugs are hard to spot, because UTF-8 is usually the encoding you wanted! But don't be lazy, and don't use the fact that Perl's internal format is UTF-8 to your advantage. Encode explicitly to avoid weird bugs, and to show to maintenance programmers that you thought this through.
You can provide this layer when "open"ing the file:
open my $fh, '>:encoding(UTF-8)', $filename; # auto encoding on write open my $fh, '<:encoding(UTF-8)', $filename; # auto decoding on read
Or if you already have an open filehandle:
binmode $fh, ':encoding(UTF-8)';
Some database drivers for DBI can also automatically encode and decode, but that is sometimes limited to the UTF-8 encoding.
You could open the document in a web browser, and change the character set or character encoding until you can visually confirm that all characters look the way they should.
There is no way to reliably detect the encoding automatically, so if people keep sending you data without charset indication, you may have to educate them.
use utf8;
This doesn't do anything to your input, or to your output. It only influences the way your sources are read. You can use Unicode in string literals, in identifiers (but they still have to be ``word characters'' according to "\w"), and even in custom delimiters.
Here's what happens: when Perl reads in a string literal, it sticks to 8 bit encoding as long as it can. (But perhaps originally it was internally encoded as UTF-8, when you dumped it.) When it has to give that up because other characters are added to the text string, it silently upgrades the string to UTF-8.
If you properly encode your strings for output, none of this is of your concern, and you can just "eval" dumped data as always.
The rationale for requiring this is to not break older programs that rely on the way things worked before Unicode came along. Those older programs knew only about the ASCII character set, and so may not work properly for additional characters. When a string is encoded in UTF-8, Perl assumes that the program is prepared to deal with Unicode, but when the string isn't, Perl assumes that only ASCII is wanted, and so those characters that are not ASCII characters aren't recognized as to what they would be in Unicode. "use feature 'unicode_strings'" tells Perl to treat all characters as Unicode, whether the string is encoded in UTF-8 or not, thus avoiding the problem.
However, on earlier Perls, or if you pass strings to subroutines outside the feature's scope, you can force Unicode rules by changing the encoding to UTF-8 by doing "utf8::upgrade($string)". This can be used safely on any string, as it checks and does not change strings that have already been upgraded.
For a more detailed discussion, see Unicode::Semantics on CPAN.
This is something you, the programmer, has to keep track of; sorry. You could consider adopting a kind of ``Hungarian notation'' to help with this.
my $text_string = decode('FOO', $foo_string);
my $bar_string = encode('BAR', $text_string);
or by skipping the text string part, and going directly from one binary encoding to the other:
use Encode qw(from_to);
from_to($string, 'FOO', 'BAR'); # changes contents of $string
or by letting automatic decoding and encoding do all the work:
open my $foofh, '<:encoding(FOO)', 'example.foo.txt';
open my $barfh, '>:encoding(BAR)', 'example.bar.txt';
print { $barfh } $_ while <$foofh>;
The Perl warning ``Wide character in ...'' is caused by such a character. With no specified encoding layer, Perl tries to fit things into a single byte. When it can't, it emits this warning (if warnings are enabled), and uses UTF-8 encoded data instead.
To avoid this warning and to avoid having different output encodings in a single stream, always specify an encoding explicitly, for example with a PerlIO layer:
binmode STDOUT, ":encoding(UTF-8)";
The UTF8 flag, also called SvUTF8, is an internal flag that indicates that the current internal representation is UTF-8. Without the flag, it is assumed to be ISO-8859-1. Perl converts between these automatically. (Actually Perl usually assumes the representation is ASCII; see ``Why do regex character classes sometimes match only in the ASCII range?'' above.)
One of Perl's internal formats happens to be UTF-8. Unfortunately, Perl can't keep a secret, so everyone knows about this. That is the source of much confusion. It's better to pretend that the internal format is some unknown encoding, and that you always have to encode and decode explicitly.
"use bytes" is usually a failed attempt to do something useful. Just forget about it.
If you need non-ASCII characters in your source code, make it a UTF-8 encoded file and "use utf8".
If you need to set the encoding for STDIN, STDOUT, and STDERR, for example based on the user's locale, "use open".
Instead of ":encoding(UTF-8)", you can simply use ":utf8", which skips the encoding step if the data was already represented as UTF8 internally. This is widely accepted as good behavior when you're writing, but it can be dangerous when reading, because it causes internal inconsistency when you have invalid byte sequences. Using ":utf8" for input can sometimes result in security breaches, so please use ":encoding(UTF-8)" instead.
Instead of "decode" and "encode", you could use "_utf8_on" and "_utf8_off", but this is considered bad style. Especially "_utf8_on" can be dangerous, for the same reason that ":utf8" can.
There are some shortcuts for oneliners; see -C in perlrun.
"UTF-8" is internally known as "utf-8-strict". The tutorial uses UTF-8 consistently, even where utf8 is actually used internally, because the distinction can be hard to make, and is mostly irrelevant.
For example, utf8 can be used for code points that don't exist in Unicode, like 9999999, but if you encode that to UTF-8, you get a substitution character (by default; see ``Handling Malformed Data'' in Encode for more ways of dealing with this.)
Okay, if you insist: the ``internal format'' is utf8, not UTF-8. (When it's not some other encoding.)
Perl knows how it stored the string internally, and will use that knowledge when you "encode". In other words: don't try to find out what the internal encoding for a certain string is, but instead just encode it into the encoding that you want.