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8.19. Setting the Default I/O Layers

8.19.1. Problem

You want to ensure all files opened by
your program use a particular set of I/O layers. For example, you
know that every file will contain UTF-8 data.

8.19.2. Solution

Use the
open pragma:

use open IO => ":raw:utf8";

8.19.3. Discussion

You can easily specify I/O layers when you open a filehandle
directly, but that doesn''t help you when the filehandle is opened by
someone else''s code (possibly even the Perl core). The
open pragma lets you specify a default set of
layers for every open that doesn''t specify its own
layers.

The open module also offers separate
IN and OUT control for input
and output handles. For example, to read bytes and emit UTF-8:

use open "IN" => ":bytes", "OUT" => ":utf8";

The :std option tells open to
apply the input and output layers to STDIN and
STDOUT/STDERR. For example, the
following code makes input handles read Greek (ISO 8859-7) and output
handles write in the UTF-8 Unicode encoding. Then it applies the same
layers to STDIN, STDOUT, and
STDERR:

use open "IN" => ":encoding(Greek)",     # reading Greek
"OUT" => ":utf8",               # writing 8-bit data in Unicode UTF-8,
":std";                         # STDIN is Greek,

8.19.4. See Also

The documentation for the standard open pragma;
Recipe 8.12 and Recipe 8.19