open - perl pragma to set default disciplines for input and output
use open IN => ":crlf", OUT => ":raw"; use open INOUT => ":utf8";
Full-fledged support for I/O disciplines is now implemented provided Perl is configured to use PerlIO as its IO system (which is now the default).
open pragma serves as one of the interfaces to declare default "layers" (aka disciplines) for all I/O.
open pragma is used to declare one or more default layers for I/O operations. Any open(), readpipe() (aka qx//) and similar operators found within the lexical scope of this pragma will use the declared defaults.
When open() is given an explicit list of layers they are appended to the list declared using this pragma.
Directory handles may also support disciplines in future.
If Perl is not built to use PerlIO as its IO system then only the two pseudo-disciplines ":raw" and ":crlf" are available.
The ":raw" discipline corresponds to "binary mode" and the ":crlf" discipline 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 disciplines 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
find which is implemented as XS code. It is called by
import to validate the layers:
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.