5 # Map layer name to package that defines it
14 if (exists $alias{$layer})
16 $layer = $alias{$layer}
20 $layer = "${class}::$layer";
22 eval "require $layer";
32 PerlIO - On demand loader for PerlIO layers and root of PerlIO::* name space
36 open($fh,">:crlf", "my.txt")
37 open($fh,">:bytes","his.jpg")
40 PERLIO=perlio perl ....
44 When an undefined layer 'foo' is encountered in an C<open> or
45 C<binmode> layer specification then C code performs the equivalent of:
49 The perl code in PerlIO.pm then attempts to locate a layer by doing
53 Otherwise the C<PerlIO> package is a place holder for additional
54 PerlIO related functions.
56 The following layers are currently defined:
62 Low level layer which calls C<read>, C<write> and C<lseek> etc.
66 Layer which calls C<fread>, C<fwrite> and C<fseek>/C<ftell> etc. Note
67 that as this is "real" stdio it will ignore any layers beneath it and
68 got straight to the operating system via the C library as usual.
72 This is a re-implementation of "stdio-like" buffering written as a
73 PerlIO "layer". As such it will call whatever layer is below it for
78 A layer which does CRLF to "\n" translation distinguishing "text" and
79 "binary" files in the manner of MS-DOS and similar operating systems.
83 Declares that the stream accepts perl's internal encoding of
84 characters. (Which really is UTF-8 on ASCII machines, but is
85 UTF-EBCDIC on EBCDIC machines.) This allows any character perl can
86 represent to be read from or written to the stream. The UTF-X encoding
87 is chosen to render simple text parts (i.e. non-accented letters,
88 digits and common punctuation) human readable in the encoded file.
90 Here is how to write your native data out using UTF-8 (or UTF-EBCDIC)
91 and then read it back in.
93 open(F, ">:utf8", "data.utf");
97 open(F, "<:utf8", "data.utf");
103 This is the inverse of C<:utf8> layer. It turns off the flag
104 on the layer below so that data read from it is considered to
105 be "octets" i.e. characters in range 0..255 only. Likewise
106 on output perl will warn if a "wide" character is written
111 B<Note that the explicit use of the C<raw> layer is deprecated.>
113 A pseudo-layer which performs two functions (which is messy, but
114 necessary to maintain compatibility with non-PerlIO builds of Perl
115 and their way things have been documented elsewhere).
117 Firstly it forces the file handle to be considered binary at that
118 point in the layer stack, i.e. it turns off any CRLF translation.
120 Secondly in prevents the IO system seaching back before it in the
121 layer specification. Thus:
123 open($fh,":raw:perlio",...)
125 Forces the use of C<perlio> layer even if the platform default, or
126 C<use open> default is something else (such as ":encoding(iso-8859-7)")
127 (the C<:encoding> requires C<use Encode>) which would interfere with
128 binary nature of the stream.
132 =head2 Defaults and how to override them
134 If the platform is MS-DOS like and normally does CRLF to "\n"
135 translation for text files then the default layers are :
139 (The low level "unix" layer may be replaced by a platform specific low
142 Otherwise if C<Configure> found out how to do "fast" IO using system's
143 stdio, then the default layers are :
147 Otherwise the default layers are
151 These defaults may change once perlio has been better tested and tuned.
153 The default can be overridden by setting the environment variable
154 PERLIO to a space separated list of layers (unix or platform low level
155 layer is always pushed first).
157 This can be used to see the effect of/bugs in the various layers e.g.
160 PERLIO=stdio ./perl harness
161 PERLIO=perlio ./perl harness
165 Nick Ing-Simmons E<lt>nick@ing-simmons.netE<gt>
169 L<perlfunc/"binmode">, L<perlfunc/"open">, L<perlunicode>, L<Encode>