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1 | package PerlIO; |
2 | |
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3 | our $VERSION = '1.00'; |
4 | |
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5 | # Map layer name to package that defines it |
6 | my %alias = (encoding => 'Encode'); |
7 | |
8 | sub import |
9 | { |
10 | my $class = shift; |
11 | while (@_) |
12 | { |
13 | my $layer = shift; |
14 | if (exists $alias{$layer}) |
15 | { |
16 | $layer = $alias{$layer} |
17 | } |
18 | else |
19 | { |
20 | $layer = "${class}::$layer"; |
21 | } |
22 | eval "require $layer"; |
23 | warn $@ if $@; |
24 | } |
25 | } |
26 | |
27 | 1; |
28 | __END__ |
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29 | |
30 | =head1 NAME |
31 | |
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32 | PerlIO - On demand loader for PerlIO layers and root of PerlIO::* name space |
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33 | |
34 | =head1 SYNOPSIS |
35 | |
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36 | open($fh,">:crlf","my.txt") |
37 | open($fh,">:raw","his.jpg") |
38 | |
39 | Shell: |
40 | PERLIO=perlio perl .... |
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41 | |
42 | =head1 DESCRIPTION |
43 | |
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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: |
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46 | |
47 | use PerlIO 'foo'; |
48 | |
49 | The perl code in PerlIO.pm then attempts to locate a layer by doing |
50 | |
51 | require PerlIO::foo; |
52 | |
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53 | Otherwise the C<PerlIO> package is a place holder for additional |
54 | PerlIO related functions. |
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55 | |
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56 | The following layers are currently defined: |
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57 | |
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58 | =over 4 |
59 | |
60 | =item unix |
61 | |
62 | Low level layer which calls C<read>, C<write> and C<lseek> etc. |
63 | |
64 | =item stdio |
65 | |
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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 |
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68 | got straight to the operating system via the C library as usual. |
69 | |
70 | =item perlio |
71 | |
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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 |
74 | its operations. |
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75 | |
76 | =item crlf |
77 | |
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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. |
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80 | |
81 | =item utf8 |
82 | |
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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. |
89 | |
90 | Here is how to write your native data out using UTF-8 (or UTF-EBCDIC) |
91 | and then read it back in. |
92 | |
93 | open(F, ">:utf8", "data.utf"); |
94 | print F $out; |
95 | close(F); |
96 | |
97 | open(F, "<:utf8", "data.utf"); |
98 | $in = <F>; |
99 | close(F); |
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100 | |
101 | =item raw |
102 | |
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103 | A pseudo-layer which performs two functions (which is messy, but |
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104 | necessary to maintain compatibility with non-PerlIO builds of Perl |
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105 | and their way things have been documented elsewhere). |
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106 | |
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107 | Firstly it forces the file handle to be considered binary at that |
108 | point in the layer stack, |
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109 | |
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110 | Secondly in prevents the IO system seaching back before it in the |
111 | layer specification. Thus: |
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112 | |
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113 | open($fh,":raw:perlio",...) |
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114 | |
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115 | Forces the use of C<perlio> layer even if the platform default, or |
116 | C<use open> default is something else (such as ":encoding(iso-8859-7)") |
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117 | (the C<:encoding> requires C<use Encode>) which would interfere with |
118 | binary nature of the stream. |
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119 | |
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120 | =back |
121 | |
122 | =head2 Defaults and how to override them |
123 | |
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124 | If the platform is MS-DOS like and normally does CRLF to "\n" |
125 | translation for text files then the default layers are : |
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126 | |
127 | unix crlf |
128 | |
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129 | (The low level "unix" layer may be replaced by a platform specific low |
130 | level layer.) |
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131 | |
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132 | Otherwise if C<Configure> found out how to do "fast" IO using system's |
133 | stdio, then the default layers are : |
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134 | |
135 | unix stdio |
136 | |
137 | Otherwise the default layers are |
138 | |
139 | unix perlio |
140 | |
141 | These defaults may change once perlio has been better tested and tuned. |
142 | |
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143 | The default can be overridden by setting the environment variable |
144 | PERLIO to a space separated list of layers (unix or platform low level |
145 | layer is always pushed first). |
146 | |
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147 | This can be used to see the effect of/bugs in the various layers e.g. |
148 | |
149 | cd .../perl/t |
150 | PERLIO=stdio ./perl harness |
151 | PERLIO=perlio ./perl harness |
152 | |
153 | =head1 AUTHOR |
154 | |
155 | Nick Ing-Simmons E<lt>nick@ing-simmons.netE<gt> |
156 | |
157 | =head1 SEE ALSO |
158 | |
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159 | L<perlfunc/"binmode">, L<perlfunc/"open">, L<perlunicode>, L<Encode> |
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160 | |
161 | =cut |
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162 | |