open - perl pragma to set default disciplines for input and output
use open IN => ":crlf", OUT => ":raw";
The open pragma is used to declare one or more default disciplines for I/O operations. Any open() and readpipe() (aka qx//) operators found within the lexical scope of this pragma will use the declared defaults. Neither open() with an explicit set of disciplines, nor sysopen() are influenced by this pragma.
Only the two pseudo-disciplines ":raw" and ":crlf" are currently 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 currently no-ops on platforms where binmode() is a no-op, but will be supported everywhere in future.
Full-fledged support for I/O disciplines is currently unimplemented. When they are eventually supported, this pragma will serve as one of the interfaces to declare default disciplines for all I/O.
In future, any default disciplines declared by this pragma will be available by the special discipline name ":DEFAULT", and could be used within handle constructors that allow disciplines to be specified. This would make it possible to stack new disciplines over the default ones.
open FH, "<:para :DEFAULT", $file or die "can't open $file: $!";
Socket and directory handles will also support disciplines in future.
Full support for I/O disciplines will enable all of the supported disciplines to work on all platforms.