From 7d3b96bbd83d17f17b26b4c05ef623881c8477be Mon Sep 17 00:00:00 2001
From: Nick Ing-Simmons <nik@tiuk.ti.com>
Date: Wed, 28 Mar 2001 18:24:02 +0000
Subject: PerlIO.pm / perlio.pm conflict. Update some pods. Make
 t/op/utf8decode.t a text file.

p4raw-id: //depot/perlio@9417
---
 lib/PerlIO.pm | 98 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 95 insertions(+), 3 deletions(-)

(limited to 'lib/PerlIO.pm')

diff --git a/lib/PerlIO.pm b/lib/PerlIO.pm
index 65b7ec3530..04cd4cfcc4 100644
--- a/lib/PerlIO.pm
+++ b/lib/PerlIO.pm
@@ -27,11 +27,15 @@ __END__
 
 =head1 NAME
 
-PerlIO - On demand loader for PerlIO::* name space
+PerlIO - On demand loader for PerlIO layers and root of PerlIO::* name space
 
 =head1 SYNOPSIS
 
-  open($fh,">:foo",...)
+  open($fh,">:crlf","my.txt")
+  open($fh,">:raw","his.jpg")
+
+  Shell:
+    PERLIO=perlio perl ....
 
 =head1 DESCRIPTION
 
@@ -47,7 +51,95 @@ The perl code in PerlIO.pm then attempts to locate a layer by doing
 Otherwise the C<PerlIO> package is a place holder for additional PerLIO related
 functions.
 
+The following layers are currently defined:
 
-=cut
+=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.
+
+=item crlf
+
+A layer which does CRLF to "\n" translation distinguishing "text" and "binary"
+files in the manner of MS-DOS and similar operating systems.
+
+=item utf8
+
+Declares that the stream accepts perl's internal encoding of characters.
+(Which really is UTF-8 on ASCII machines, but is UTF-EBCDIC on EBCDIC machines.)
+This allows any character perl can represent to be read from or written to the
+stream. The UTF-X encoding is chosen to render simple text parts (i.e.
+non-accented letters, digits and common punctuation) human readable in the
+encoded file.
+
+=item raw
+
+A pseudo-layer which performs two functions (which is messy, but necessary to
+maintain compatibility with non-PerLIO builds of perl and they way things
+have been documented elsewhere).
+
+Firstly it forces the file handle to be considered binary at that point
+in the layer stack,
+
+Secondly in prevents the IO system seaching back before it in the layer specification.
+Thus:
+
+    open($fh,":raw:perlio"),...)
+
+Forces the use of C<perlio> layer even if the platform default, or C<use open> default
+is something else (such as ":encoding(iso-8859-7)" ) which would interfere with
+binary nature of the stream.
 
+=back
+
+=head2 Defaults and how to override them
+
+If the platform is MS-DOS like and normally does CRLF to "\n" translation
+for text files then the default layers are :
+
+  unix crlf
+
+(The low level "unix" layer may be replaced by a platform specific low level layer.)
+
+Otherwise 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
+
+These defaults 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 or platform low level layer 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>
+
+=head1 SEE ALSO
+
+L<perlfunc/"binmode">, L<perlfunc/"open">, L<perlunicode>, L<open>
+
+=cut
 
-- 
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