1;
__END__
+
+=head1 NAME
+
+PerlIO - On demand loader for PerlIO layers and root of PerlIO::* name space
+
+=head1 SYNOPSIS
+
+ open($fh,">:crlf","my.txt")
+ open($fh,">:raw","his.jpg")
+
+ Shell:
+ PERLIO=perlio perl ....
+
+=head1 DESCRIPTION
+
+When an undefined layer 'foo' is encountered in an C<open> or
+C<binmode> layer specification then C code performs the equivalent of:
+
+ use PerlIO 'foo';
+
+The perl code in PerlIO.pm then attempts to locate a layer by doing
+
+ require PerlIO::foo;
+
+Otherwise the C<PerlIO> package is a place holder for additional
+PerlIO related functions.
+
+The following layers are 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.
+
+=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.
+
+Here is how to write your native data out using UTF-8 (or UTF-EBCDIC)
+and then read it back in.
+
+ open(F, ">:utf8", "data.utf");
+ print F $out;
+ close(F);
+
+ open(F, "<:utf8", "data.utf");
+ $in = <F>;
+ close(F);
+
+=item raw
+
+A pseudo-layer which performs two functions (which is messy, but
+necessary to maintain compatibility with non-PerlIO builds of Perl
+and their way things have been documented elsewhere).
+
+Firstly it forces the file handle to be considered binary at that
+point in the layer stack,
+
+Secondly in prevents the IO system seaching back before it in the
+layer specification. Thus:
+
+ open($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)")
+(the C<:encoding> requires C<use Encode>) 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<Encode>
+
+=cut
+
https://perl5.git.perl.org / perl5.git / blobdiff