Encode::PerlIO 5.8.1

Encode::PerlIO is a detailed document on Encode and PerlIO.

Overview

It is very common to want to do encoding transformations when reading or writing files, network connections, pipes etc. If Perl is configured to use the new perlio IO system then Encode provides a "layer" (see PerlIO) which can transform data as it is read or written.

Here is how the blind poet would modernise the encoding:

use Encode;
open(my $iliad,<:encoding(iso-8859-7),iliad.greek);
open(my $utf8,>:utf8,iliad.utf8);
my @epic = < $iliad >;
print $utf8 @epic;
close($utf8);
close($illiad);

In addition, the new IO system can also be configured to read/write UTF-8 encoded characters (as noted above, this is efficient):

open(my $fh,>:utf8,anything);
print $fh "Any x{0021} string N{SMILEY FACE}n";

Either of the above forms of "layer" specifications can be made the default for a lexical scope with the use open ... pragma. See open.

Once a handle is open, its layers can be altered using binmode.

Without any such configuration, or if Perl itself is built using the systems own IO, then write operations assume that the file handle accepts only bytes and will die if a character larger than 255 is written to the handle. When reading, each octet from the handle becomes a byte-in-a-character. Note that this default is the same behaviour as bytes-only languages (including Perl before v5.6) would have, and is sufficient to handle native 8-bit encodings e.g. iso-8859-1, EBCDIC etc. and any legacy mechanisms for handling other encodings and binary data.
In other cases, it is the programs responsibility to transform characters into bytes using the API above before doing writes, and to transform the bytes read from a handle into characters before doing "character operations" (e.g. lc, /W+/, ...).

You can also use PerlIO to convert larger amounts of data you dont want to bring into memory. For example, to convert between ISO-8859-1 (Latin 1) and UTF-8 (or UTF-EBCDIC in EBCDIC machines):

open(F, "<:encoding(iso-8859-1)", "data.txt") or die $!;
open(G, ">:utf8", "data.utf") or die $!;
while (< F >) { print G }

# Could also do "print G < F >" but that would pull
# the whole file into memory just to write it out again.

More examples:

open(my $f, "<:encoding(cp1252)")
open(my $g, ">:encoding(iso-8859-2)")
open(my $h, ">:encoding(latin9)") # iso-8859-15