From type/IO/Handle

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multi method encoding(IO::Handle:D: --> Str:D)
multi method encoding(IO::Handle:D: $enc --> Str:D)

Returns a Str representing the encoding currently used by the handle, defaulting to "utf8". Nil indicates the filehandle is currently in binary mode. Specifying an optional positional $enc argument switches the encoding used by the handle; specify Nil as encoding to put the handle into binary mode.

The accepted values for encoding are case-insensitive. The available encodings vary by implementation and backend. On Rakudo MoarVM the following are supported:

utf8
utf16
utf16le
utf16be
utf8-c8
iso-8859-1
windows-1251
windows-1252
windows-932
ascii

The default encoding is utf8, which undergoes normalization into Unicode NFC (normalization form canonical). In some cases you may want to ensure no normalization is done; for this you can use utf8-c8. Before using utf8-c8 please read Unicode: Filehandles and I/O for more information on utf8-c8 and NFC.

As of Rakudo 2018.04 windows-932 is also supported which is a variant of ShiftJIS.

Implementation may choose to also provide support for aliases, e.g. Rakudo allows aliases latin-1 for iso-8859-1 encoding and dashed utf versions: utf-8 and utf-16.

From type/IO/CatHandle

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multi method encoding(IO::CatHandle:D:)
multi method encoding(IO::CatHandle:D: $new-encoding)

Sets the invocant's $.encoding attribute to the provided value. Valid values are the same as those accepted by IO::Handle.encoding (use value Nil to switch to binary mode). All source handles, including the active one will use the provided $.encoding value.

(my $f1 = 'foo'.IO).spurt: 'I ♥ Raku';
(my $f2 = 'bar'.IO).spurt: 'meow';
with IO::CatHandle.new: $f1, $f2 {
    # .encoding is 'utf8' by default: 
    .readchars(5).say; # OUTPUT: «I ♥ R␤» 
 
    .encoding: Nil; # switch to binary mode 
    .slurp.say; # OUTPUT: «Buf[uint8]:0x<6B 75 6D 65 6F 77>␤» 
}