more precisely. (Pending approval).
p4raw-id: //depot/perlio@17295
A layer which does CRLF to "\n" translation distinguishing "text" and
"binary" files in the manner of MS-DOS and similar operating systems.
+(It currently does I<not> mimic MS-DOS as far as treating of Control-Z
+as being an end-of-file marker.)
=item utf8
=item raw
-B<Note that the explicit use of the C<raw> layer is deprecated:>
+The C<:raw> layer is I<defined> as being identical to calling
+C<binmode($fh)> - the stream is made suitable for passing binary
+data i.e. each byte is passed as-is. The stream will still be
+buffered. Unlike earlier versions of perl C<:raw> is I<not> just the
+inverse of C<:crlf> - other layers which would affect the binary nature of
+the stream are also removed or disabled.
-C<:raw> has been documented as both the opposite of C<:crlf> and
-as a way to make a stream "binary". With the new IO system those
-two are no longer equivalent. The name has also been read as meaning
-an unbuffered stream "as close to the operating system as possible".
-See below for better ways to do things.
+The implementation of C<:raw> is as a pseudo-layer which when "pushed"
+pops itself and then any layers which do not declare themselves as suitable
+for binary data. (Undoing :utf8 and :crlf are implemented by clearing
+flags rather than poping layers but that is an implementation detail.)
-The C<:raw> layer exists to maintain compatibility with non-PerlIO builds
-of Perl and to approximate the way it has been documented and how
-it was "faked" in perl5.6. It is a pseudo-layer which performs two
-functions (which is messy).
+As a consequence of the fact that C<:raw> normally pops layers
+it usually only makes sense to have it as the only or first element in a
+layer specification. When used as the first element it provides
+a known base on which to build e.g.
-Firstly it forces the file handle to be considered binary at that
-point in the layer stack, i.e. it turns off any CRLF translation.
+ open($fh,":raw:utf8",...)
-Secondly in prevents the IO system seaching back before it in the
-layer specification. This second effect is intended to disable other
-non-binary features of the stream.
-
-Thus:
-
- open($fh,":raw:perlio",...)
-
-forces the use of C<perlio> layer even if the platform default, or
-C<use open> default is something else (such as ":encoding(iso-8859-7)")
-(the C<:encoding> requires C<use Encode>) which would interfere with
-binary nature of the stream.
+will construct a "binary" stream, but then enable UTF-8 translation.
=back
=head2 Alternatives to raw
-To get a binary stream the prefered method is to use:
+To get a binary stream an alternate method is to use:
+ open($fh,"whatever")
binmode($fh);
-which is neatly backward compatible with how such things have
+this has advantage of being backward compatible with how such things have
had to be coded on some platforms for years.
-The current implementation comprehends the effects of C<:utf8> and
-C<:crlf> layers and will be extended to comprehend similar translations
-if they are defined in future releases of perl.
To get an un-buffered stream specify an unbuffered layer (e.g. C<:unix>)
-the open call:
+in the open call:
open($fh,"<:unix",$path)
-To get a non-CRLF translated stream on any platform start from
-the un-buffered stream and add the appropriate layer:
-
- open($fh,"<:unix:perlio",$path)
-
-
=head2 Defaults and how to override them
If the platform is MS-DOS like and normally does CRLF to "\n"
=item *
-The PerlIO C<:raw> discipline (as described in Camel III) is deprecated
-because its definition (as either the discipline version of C<binmode(FH)>
-or as the opposite of C<:crlf>) didn't really work: most importantly
-because turning off "clrfness" is not enough to make a stream truly
-binary. Instead of C<:raw> use one of the following: C<open(..., ':bytes')>,
-C<binmode(FH)>, C<sysopen()> + C<sysread()>.
+Previous versions of perl and some readings of some sections of Camel III
+implied that C<:raw> "discipline" was the inverse of C<:crlf>.
+Turning off "clrfness" is no longer enough to make a stream truly
+binary. So the PerlIO C<:raw> discipline is now formally defined as being
+equivalent to binmode(FH) - which is in turn defined as doing whatever
+is necessary to pass each byte as-is without any translation.
+In particular binmode(FH) - and hence C<:raw> - will now turn off both CRLF
+and UTF-8 translation and remove other "layers" (e.g. :encoding()) which
+would modify byte stream.
=item *
taken as the name of the filehandle. Returns true on success,
C<undef> on failure.
-If DISCIPLINE is omitted the filehandle is made suitable for passing
-binary data. This includes turning off possible CRLF translation and
-marking it as bytes (as opposed to Unicode characters).
+If DISCIPLINE is omitted or specified as C<:raw> the filehandle is made
+suitable for passing binary data. This includes turning off possible CRLF
+translation and marking it as bytes (as opposed to Unicode characters).
+Note that as desipite what may be implied in I<"Programming Perl">
+(the Camel) or elsewhere C<:raw> is I<not> the simply inverse of C<:crlf>
+- other disciplines which would affect binary nature of the stream are
+I<also> disabled. See L<PerlIO>, L<perlrun> and the discussion about the
+PERLIO environment variable.
On some systems (in general, DOS and Windows-based systems) binmode()
is necessary when you're not working with a text file. For the sake
layers and disiplines.) The C<open> pragma can be used to establish
default I/O disciplines. See L<open>.
-The C<:raw> discipline is deprecated. (As opposed to what Camel III
-said, it is not the inverse of C<:crlf>.) See L<PerlIO>, L<perlrun>
-and the discussion about the PERLIO environment variable.
-
In general, binmode() should be called after open() but before any I/O
is done on the filehandle. Calling binmode() will normally flush any
pending buffered output data (and perhaps pending input data) on the
=item :raw
-B<Note that the explicit use of the C<:raw> layer is deprecated.>
+Applying the <:raw> layer is equivalent to calling C<binmode($fh)>.
+It makes the stream pass each byte as-is without any translation.
+In particular CRLF translation, and/or :utf8 inuited from locale
+are disabled.
-Arranges for all accesses go straight to the lowest level layer provided
+Arranges for all accesses go straight to the lowest buffered layer provided
by the configration. That is it strips off any layers above that layer.
-(The intent - unless layers are then pushed on top again -
-is to make perl's C<read> behave like C<sysread>.)
-
-Not really useful in PERLIO environment variable, instead just use
-C<:unix> layer explicitly.
In Perl 5.6 and some books the C<:raw> layer (also called a discipline)
-is documented as the inverse of the C<:crlf> layer. That is not really
-the case. If you want UNIX line endings on a platform that normally
-does CRLF translation the appropriate thing to do is to add C<:perlio>
-to PERLIO environment variable.
+is documented as the inverse of the C<:crlf> layer. That is no longer
+the case - other layers which would alter binary nature of the
+stream are also disabled. If you want UNIX line endings on a platform
+that normally does CRLF translation, but still want UTF-8 or encoding
+defaults the appropriate thing to do is to add C<:perlio> to PERLIO
+environment variable.
=item :stdio
projects / p5sagit/p5-mst-13.2.git / commitdiff