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package perlio;
1;
__END__
=head1 NAME
perlio - perl pragma to configure C level IO
=head1 SYNOPSIS
Shell:
PERLIO=perlio perl ....
print "Have ",join(',',keys %perlio::layers),"\n";
print "Using ",join(',',@perlio::layers),"\n";
=head1 DESCRIPTION
Mainly a Place holder for now.
The C<%perlio::layers> hash is a record of the available "layers" that may be pushed
onto a C<PerlIO> stream.
The C<@perlio::layers> array is the current set of layers that are used when
a new C<PerlIO> stream is opened. The C code looks are the array each time
a stream is opened so the "stack" can be manipulated by messing with the array :
pop(@perlio::layers);
push(@perlio::layers,$perlio::layers{'stdio'});
The values if both the hash and the array are perl objects, of class C<perlio::Layer>
which are created by the C code in C<perlio.c>. As yet there is nothing useful you
can do with the objects at the perl level.
There are three layers currently defined:
=over 4
=item unix
Low level layer which calls C<read>, C<write> and C<lseek> etc.
=item stdio
Layer which calls C<fread>, C<fwrite> and C<fseek>/C<ftell> etc.
Note that as this is "real" stdio it will ignore any layers beneath it and
got straight to the operating system via the C library as usual.
=item perlio
This is a re-implementation of "stdio-like" buffering written as a PerlIO "layer".
As such it will call whatever layer is below it for its operations.
=back
=head2 Defaults and how to override them
If C<Configure> found out how to do "fast" IO using system's stdio, then
the default layers are :
unix stdio
Otherwise the default layers are
unix perlio
(STDERR will have just unix in this case as that is optimal way to make it
"unbuffered" - do not add a buffering layer!)
The default may change once perlio has been better tested and tuned.
The default can be overridden by setting the environment variable PERLIO
to a space separated list of layers (unix is always pushed first).
This can be used to see the effect of/bugs in the various layers e.g.
cd .../perl/t
PERLIO=stdio ./perl harness
PERLIO=perlio ./perl harness
=head1 AUTHOR
Nick Ing-Simmons E<lt>nick@ing-simmons.netE<gt>
=cut
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