3 # Map layer name to package that defines it
4 my %alias = (encoding => 'Encode');
12 if (exists $alias{$layer})
14 $layer = $alias{$layer}
18 $layer = "${class}::$layer";
20 eval "require $layer";
30 PerlIO - On demand loader for PerlIO layers and root of PerlIO::* name space
34 open($fh,">:crlf","my.txt")
35 open($fh,">:raw","his.jpg")
38 PERLIO=perlio perl ....
42 When an undefined layer 'foo' is encountered in an C<open> or
43 C<binmode> layer specification then C code performs the equivalent of:
47 The perl code in PerlIO.pm then attempts to locate a layer by doing
51 Otherwise the C<PerlIO> package is a place holder for additional
52 PerlIO related functions.
54 The following layers are currently defined:
60 Low level layer which calls C<read>, C<write> and C<lseek> etc.
64 Layer which calls C<fread>, C<fwrite> and C<fseek>/C<ftell> etc. Note
65 that as this is "real" stdio it will ignore any layers beneath it and
66 got straight to the operating system via the C library as usual.
70 This is a re-implementation of "stdio-like" buffering written as a
71 PerlIO "layer". As such it will call whatever layer is below it for
76 A layer which does CRLF to "\n" translation distinguishing "text" and
77 "binary" files in the manner of MS-DOS and similar operating systems.
81 Declares that the stream accepts perl's internal encoding of
82 characters. (Which really is UTF-8 on ASCII machines, but is
83 UTF-EBCDIC on EBCDIC machines.) This allows any character perl can
84 represent to be read from or written to the stream. The UTF-X encoding
85 is chosen to render simple text parts (i.e. non-accented letters,
86 digits and common punctuation) human readable in the encoded file.
88 Here is how to write your native data out using UTF-8 (or UTF-EBCDIC)
89 and then read it back in.
91 open(F, ">:utf8", "data.utf");
95 open(F, "<:utf8", "data.utf");
101 A pseudo-layer which performs two functions (which is messy, but
102 necessary to maintain compatibility with non-PerlIO builds of Perl
103 and their way things have been documented elsewhere).
105 Firstly it forces the file handle to be considered binary at that
106 point in the layer stack,
108 Secondly in prevents the IO system seaching back before it in the
109 layer specification. Thus:
111 open($fh,":raw:perlio",...)
113 Forces the use of C<perlio> layer even if the platform default, or
114 C<use open> default is something else (such as ":encoding(iso-8859-7)")
115 which would interfere with binary nature of the stream.
119 =head2 Defaults and how to override them
121 If the platform is MS-DOS like and normally does CRLF to "\n"
122 translation for text files then the default layers are :
126 (The low level "unix" layer may be replaced by a platform specific low
129 Otherwise if C<Configure> found out how to do "fast" IO using system's
130 stdio, then the default layers are :
134 Otherwise the default layers are
138 These defaults may change once perlio has been better tested and tuned.
140 The default can be overridden by setting the environment variable
141 PERLIO to a space separated list of layers (unix or platform low level
142 layer is always pushed first).
144 This can be used to see the effect of/bugs in the various layers e.g.
147 PERLIO=stdio ./perl harness
148 PERLIO=perlio ./perl harness
152 Nick Ing-Simmons E<lt>nick@ing-simmons.netE<gt>
156 L<perlfunc/"binmode">, L<perlfunc/"open">, L<perlunicode>, L<Encode>