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1 | package PerlIO; |
2 | |
3 | # Map layer name to package that defines it |
4 | my %alias = (encoding => 'Encode'); |
5 | |
6 | sub import |
7 | { |
8 | my $class = shift; |
9 | while (@_) |
10 | { |
11 | my $layer = shift; |
12 | if (exists $alias{$layer}) |
13 | { |
14 | $layer = $alias{$layer} |
15 | } |
16 | else |
17 | { |
18 | $layer = "${class}::$layer"; |
19 | } |
20 | eval "require $layer"; |
21 | warn $@ if $@; |
22 | } |
23 | } |
24 | |
25 | 1; |
26 | __END__ |
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27 | |
28 | =head1 NAME |
29 | |
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30 | PerlIO - On demand loader for PerlIO layers and root of PerlIO::* name space |
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31 | |
32 | =head1 SYNOPSIS |
33 | |
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34 | open($fh,">:crlf","my.txt") |
35 | open($fh,">:raw","his.jpg") |
36 | |
37 | Shell: |
38 | PERLIO=perlio perl .... |
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39 | |
40 | =head1 DESCRIPTION |
41 | |
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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: |
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44 | |
45 | use PerlIO 'foo'; |
46 | |
47 | The perl code in PerlIO.pm then attempts to locate a layer by doing |
48 | |
49 | require PerlIO::foo; |
50 | |
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51 | Otherwise the C<PerlIO> package is a place holder for additional |
52 | PerlIO related functions. |
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53 | |
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54 | The following layers are currently defined: |
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55 | |
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56 | =over 4 |
57 | |
58 | =item unix |
59 | |
60 | Low level layer which calls C<read>, C<write> and C<lseek> etc. |
61 | |
62 | =item stdio |
63 | |
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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 |
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66 | got straight to the operating system via the C library as usual. |
67 | |
68 | =item perlio |
69 | |
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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 |
72 | its operations. |
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73 | |
74 | =item crlf |
75 | |
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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. |
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78 | |
79 | =item utf8 |
80 | |
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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. |
87 | |
88 | Here is how to write your native data out using UTF-8 (or UTF-EBCDIC) |
89 | and then read it back in. |
90 | |
91 | open(F, ">:utf8", "data.utf"); |
92 | print F $out; |
93 | close(F); |
94 | |
95 | open(F, "<:utf8", "data.utf"); |
96 | $in = <F>; |
97 | close(F); |
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98 | |
99 | =item raw |
100 | |
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101 | A pseudo-layer which performs two functions (which is messy, but |
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102 | necessary to maintain compatibility with non-PerlIO builds of Perl |
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103 | and their way things have been documented elsewhere). |
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104 | |
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105 | Firstly it forces the file handle to be considered binary at that |
106 | point in the layer stack, |
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107 | |
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108 | Secondly in prevents the IO system seaching back before it in the |
109 | layer specification. Thus: |
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110 | |
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111 | open($fh,":raw:perlio",...) |
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112 | |
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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. |
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116 | |
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117 | =back |
118 | |
119 | =head2 Defaults and how to override them |
120 | |
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121 | If the platform is MS-DOS like and normally does CRLF to "\n" |
122 | translation for text files then the default layers are : |
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123 | |
124 | unix crlf |
125 | |
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126 | (The low level "unix" layer may be replaced by a platform specific low |
127 | level layer.) |
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128 | |
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129 | Otherwise if C<Configure> found out how to do "fast" IO using system's |
130 | stdio, then the default layers are : |
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131 | |
132 | unix stdio |
133 | |
134 | Otherwise the default layers are |
135 | |
136 | unix perlio |
137 | |
138 | These defaults may change once perlio has been better tested and tuned. |
139 | |
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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). |
143 | |
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144 | This can be used to see the effect of/bugs in the various layers e.g. |
145 | |
146 | cd .../perl/t |
147 | PERLIO=stdio ./perl harness |
148 | PERLIO=perlio ./perl harness |
149 | |
150 | =head1 AUTHOR |
151 | |
152 | Nick Ing-Simmons E<lt>nick@ing-simmons.netE<gt> |
153 | |
154 | =head1 SEE ALSO |
155 | |
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156 | L<perlfunc/"binmode">, L<perlfunc/"open">, L<perlunicode>, L<Encode> |
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157 | |
158 | =cut |
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159 | |