你可能知道，在Perl中，“utf8”意味着Perl对UTF-8的理解更为宽松，它允许在技术上不是UTF-8中有效代码点的字符。相比之下，“UTF-8”（或“utf-8”）是Perl对UTF-8更严格的理解，它不允许无效的代码点。
我有一些与此区别相关的使用问题：
open文件时会发生什么？角色替换是否发生在糟糕的角色上或是否发生了其他事情？open和'>：utf8'这样的层和像'>：encoding（utf8）'这样的层有什么区别？这两种方法都可以同时用于'utf8'和'UTF-8'吗？ ╔════════════════════════════════════════════╤══════════════════════╗
║ │ ║
║ On Read │ On Write ║
║ │ ║
Perl ╟─────────────────────┬──────────────────────┼──────────────────────╢
5.26 ║ │ │ ║
║ Invalid encoding │ Outside of Unicode, │ Outside of Unicode, ║
║ other than sequence │ Unicode nonchar, or │ Unicode nonchar, or ║
║ length │ Unicode surrogate │ Unicode surrogate ║
║ │ │ ║
╔══════════════════╬═════════════════════╪══════════════════════╪══════════════════════╣
║ ║ │ │ ║
║ :encoding(UTF-8) ║ Warns and Replaces │ Warns and Replaces │ Warns and Replaces ║
║ ║ │ │ ║
╟──────────────────╫─────────────────────┼──────────────────────┼──────────────────────╢
║ ║ │ │ ║
║ :encoding(utf8) ║ Warns and Replaces │ Accepts │ Warns and Accepts ║
║ ║ │ │ ║
╟──────────────────╫─────────────────────┼──────────────────────┼──────────────────────╢
║ ║ │ │ ║
║ :utf8 ║ Corrupt scalar │ Accepts │ Warns and Accepts ║
║ ║ │ │ ║
╚══════════════════╩═════════════════════╧══════════════════════╧══════════════════════╝
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请注意，:encoding(UTF-8)实际上使用utf8解码，然后检查范围是否允许字符（因为它识别"\x{20_000}"甚至"\x{1000_0000_0000_0000}"）。这减少了错误消息的数量，因此它很好。
（编码名称不区分大小写。）
用于生成上表的测试：
:encoding(UTF-8)
printf "\xC3\xA9\n\xEF\xBF\xBF\n\xED\xA0\x80\n\xF8\x88\x80\x80\x80\n\x80\n" |
perl -MB -nle'
use open ":std", ":encoding(UTF-8)";
my $sv = B::svref_2object(\$_);
printf "%vX%s (internal: %vX, UTF8=%d)\n", $_, length($_)==1 ? "" : " = $_", $sv->PVX, utf8::is_utf8($_);
'
utf8 "\xFFFF" does not map to Unicode.
utf8 "\xD800" does not map to Unicode.
utf8 "\x200000" does not map to Unicode.
utf8 "\x80" does not map to Unicode.
E9 (internal: C3.A9, UTF8=1)
5C.78.7B.46.46.46.46.7D = \x{FFFF} (internal: 5C.78.7B.46.46.46.46.7D, UTF8=1)
5C.78.7B.44.38.30.30.7D = \x{D800} (internal: 5C.78.7B.44.38.30.30.7D, UTF8=1)
5C.78.7B.32.30.30.30.30.30.7D = \x{200000} (internal: 5C.78.7B.32.30.30.30.30.30.7D, UTF8=1)
5C.78.38.30 = \x80 (internal: 5C.78.38.30, UTF8=1)
:encoding(utf8)
$ printf "\xC3\xA9\n\xEF\xBF\xBF\n\xED\xA0\x80\n\xF8\x88\x80\x80\x80\n\x80\n" |
perl -MB -nle'
use open ":std", ":encoding(utf8)";
my $sv = B::svref_2object(\$_);
printf "%vX%s (internal: %vX, UTF8=%d)\n", $_, length($_)==1 ? "" : " = $_", $sv->PVX, utf8::is_utf8($_);
'
utf8 "\x80" does not map to Unicode.
E9 (internal: C3.A9, UTF8=1)
FFFF (internal: EF.BF.BF, UTF8=1)
D800 (internal: ED.A0.80, UTF8=1)
200000 (internal: F8.88.80.80.80, UTF8=1)
5C.78.38.30 = \x80 (internal: 5C.78.38.30, UTF8=1)
:utf8
$ printf "\xC3\xA9\n\xEF\xBF\xBF\n\xED\xA0\x80\n\xF8\x88\x80\x80\x80\n\x80\n" |
perl -MB -nle'
use open ":std", ":encoding(utf8)";
my $sv = B::svref_2object(\$_);
printf "%vX%s (internal: %vX, UTF8=%d)\n", $_, length($_)==1 ? "" : " = $_", $sv->PVX, utf8::is_utf8($_);
'
E9 (internal: C3.A9, UTF8=1)
FFFF (internal: EF.BF.BF, UTF8=1)
D800 (internal: ED.A0.80, UTF8=1)
200000 (internal: F8.88.80.80.80, UTF8=1)
Malformed UTF-8 character: \x80 (unexpected continuation byte 0x80, with no preceding start byte) in printf at -e line 4, <> line 5.
0 (internal: 80, UTF8=1)
:encoding(UTF-8)
$ perl -e'
use open ":std", ":encoding(UTF-8)";
print "\x{E9}\n";
print "\x{FFFF}\n";
print "\x{D800}\n";
print "\x{20_0000}\n";
' >a
Unicode non-character U+FFFF is not recommended for open interchange in print at -e line 4.
Unicode surrogate U+D800 is illegal in UTF-8 at -e line 5.
Code point 0x200000 is not Unicode, may not be portable in print at -e line 6.
"\x{ffff}" does not map to utf8.
"\x{d800}" does not map to utf8.
"\x{200000}" does not map to utf8.
$ od -t c a
0000000 303 251 \n \ x { F F F F } \n \ x { D
0000020 8 0 0 } \n \ x { 2 0 0 0 0 0 } \n
0000040
$ cat a
é
\x{FFFF}
\x{D800}
\x{200000}
:encoding(utf8)
$ perl -e'
use open ":std", ":encoding(utf8)";
print "\x{E9}\n";
print "\x{FFFF}\n";
print "\x{D800}\n";
print "\x{20_0000}\n";
' >a
Unicode surrogate U+D800 is illegal in UTF-8 at -e line 4.
Code point 0x200000 is not Unicode, may not be portable in print at -e line 5.
$ od -t c a
0000000 303 251 \n 355 240 200 \n 370 210 200 200 200 \n
0000015
$ cat a
é
▒
▒
:utf8
与:encoding(utf8)相同的结果。使用Perl 5.26测试。
默认情况下，Encode :: encode将使用替换字符替换无效字符。即使您将更宽松的“utf8”作为编码传递，这是真的吗？
Perl字符串是32位或64位字符的字符串，具体取决于构建。 utf8可以编码任何72位整数。因此，它能够编码可以被要求编码的所有字符。