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RedHat 9 (Linux i386) - man page for open (redhat section 3pm)

open(3pm)			 Perl Programmers Reference Guide			open(3pm)

NAME
       open - perl pragma to set default PerlIO layers for input and output

SYNOPSIS
	   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';

DESCRIPTION
       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"  sub-
       pragma 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 Encode::Supported for details and the list of supported locales.

       Note that ":utf8" PerlIO layer must always be specified exactly like that, it is not sub-
       ject 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:

       1.  If the platform supports the langinfo(CODESET) interface, the codeset returned is used
	   as the default encoding for the open pragma.

       2.  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.

       3.  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.

NONPERLIO FUNCTIONALITY
       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.

IMPLEMENTATION DETAILS
       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.

SEE ALSO
       "binmode" in perlfunc, "open" in perlfunc, perlunicode, PerlIO, encoding

perl v5.8.0				    2002-06-01					open(3pm)


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