open - perl pragma to set default PerlIO layers for input and output |
open - perl pragma to set default PerlIO layers for input and output
use open IN => ":crlf", OUT => ":bytes"; use open OUT => ':utf8'; use open IO => ":encoding(iso-8859-7)";
use open IO => ':locale';
use open ':utf8'; use open ':locale'; use open ':encoding(iso-8859-7)';
use open ':std';
Full-fledged support for I/O layers is now implemented provided Perl is configured to use PerlIO as its IO system (which is now the default).
The open
pragma serves as one of the interfaces to declare default
``layers'' (also known as ``disciplines'') for all I/O. Any open(),
readpipe()
(aka qx//) and similar operators found within the lexical
scope of this pragma will use the declared defaults.
With the IN
subpragma you can declare the default layers
of input streams, and with the OUT
subpragma you can declare
the default layers of output streams. With the IO
subpragma
you can control both input and output streams simultaneously.
If you have a legacy encoding, you can use the :encoding(...)
tag.
if you want to set your encoding layers based on your
locale environment variables, you can use the :locale
tag.
For example:
$ENV{LANG} = 'ru_RU.KOI8-R'; # the :locale will probe the locale environment variables like LANG use open OUT => ':locale'; open(O, ">koi8"); print O chr(0x430); # Unicode CYRILLIC SMALL LETTER A = KOI8-R 0xc1 close O; open(I, "<koi8"); printf "%#x\n", ord(<I>), "\n"; # this should print 0xc1 close I;
These are equivalent
use open ':utf8'; use open IO => ':utf8';
as are these
use open ':locale'; use open IO => ':locale';
and these
use open ':encoding(iso-8859-7)'; use open IO => ':encoding(iso-8859-7)';
The matching of encoding names is loose: case does not matter, and many encodings have several aliases. See the Encode::Supported manpage for details and the list of supported locales.
Note that :utf8
PerlIO layer must always be specified exactly like
that, it is not subject to the loose matching of encoding names.
When open()
is given an explicit list of layers they are appended to
the list declared using this pragma.
The :std
subpragma on its own has no effect, but if combined with
the :utf8
or :encoding
subpragmas, it converts the standard
filehandles (STDIN, STDOUT, STDERR) to comply with encoding selected
for input/output handles. For example, if both input and out are
chosen to be :utf8
, a :std
will mean that STDIN, STDOUT, and
STDERR are also in :utf8
. On the other hand, if only output is
chosen to be in :encoding(koi8r)
, a :std
will cause only the
STDOUT and STDERR to be in koi8r
. The :locale
subpragma
implicitly turns on :std
.
The logic of :locale
is as follows:
langinfo(CODESET)
interface, the codeset
returned is used as the default encoding for the open pragma.
If 1. didn't work but we are under the locale pragma, the environment
variables LC_ALL and LANG (in that order) are matched for encodings
(the part after .
, if any), and if any found, that is used
as the default encoding for the open pragma.
If 1. and 2. didn't work, the environment variables LC_ALL and LANG
(in that order) are matched for anything looking like UTF-8, and if
any found, :utf8
is used as the default encoding for the open
pragma.
If your locale environment variables (LC_ALL, LC_CTYPE, LANG) contain the strings 'UTF-8' or 'UTF8' (case-insensitive matching), the default encoding of your STDIN, STDOUT, and STDERR, and of any subsequent file open, is UTF-8.
Directory handles may also support PerlIO layers in the future.
If Perl is not built to use PerlIO as its IO system then only the two
pseudo-layers :bytes
and :crlf
are available.
The :bytes
layer corresponds to ``binary mode'' and the :crlf
layer corresponds to ``text mode'' on platforms that distinguish
between the two modes when opening files (which is many DOS-like
platforms, including Windows). These two layers are no-ops on
platforms where binmode()
is a no-op, but perform their functions
everywhere if PerlIO is enabled.
There is a class method in PerlIO::Layer
find
which is
implemented as XS code. It is called by import
to validate the
layers:
PerlIO::Layer::->find("perlio")
The return value (if defined) is a Perl object, of class
PerlIO::Layer
which is created by the C code in perlio.c. As
yet there is nothing useful you can do with the object at the perl
level.
binmode in the perlfunc manpage, open in the perlfunc manpage, the perlunicode manpage, the PerlIO manpage, the encoding manpage
open - perl pragma to set default PerlIO layers for input and output |