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1 | package PerlIO; |
2 | |
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3 | our $VERSION = '1.01'; |
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4 | |
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5 | # Map layer name to package that defines it |
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6 | our %alias; |
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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"); # portably open a text file for writing |
37 | |
38 | open($fh,"<","his.jpg"); # portably open a binary file for reading |
39 | binmode($fh); |
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40 | |
41 | Shell: |
42 | PERLIO=perlio perl .... |
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43 | |
44 | =head1 DESCRIPTION |
45 | |
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46 | When an undefined layer 'foo' is encountered in an C<open> or |
47 | C<binmode> layer specification then C code performs the equivalent of: |
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48 | |
49 | use PerlIO 'foo'; |
50 | |
51 | The perl code in PerlIO.pm then attempts to locate a layer by doing |
52 | |
53 | require PerlIO::foo; |
54 | |
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55 | Otherwise the C<PerlIO> package is a place holder for additional |
56 | PerlIO related functions. |
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57 | |
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58 | The following layers are currently defined: |
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59 | |
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60 | =over 4 |
61 | |
62 | =item unix |
63 | |
64 | Low level layer which calls C<read>, C<write> and C<lseek> etc. |
65 | |
66 | =item stdio |
67 | |
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68 | Layer which calls C<fread>, C<fwrite> and C<fseek>/C<ftell> etc. Note |
69 | that as this is "real" stdio it will ignore any layers beneath it and |
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70 | got straight to the operating system via the C library as usual. |
71 | |
72 | =item perlio |
73 | |
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74 | This is a re-implementation of "stdio-like" buffering written as a |
75 | PerlIO "layer". As such it will call whatever layer is below it for |
76 | its operations. |
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77 | |
78 | =item crlf |
79 | |
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80 | A layer which does CRLF to "\n" translation distinguishing "text" and |
81 | "binary" files in the manner of MS-DOS and similar operating systems. |
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82 | |
83 | =item utf8 |
84 | |
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85 | Declares that the stream accepts perl's internal encoding of |
86 | characters. (Which really is UTF-8 on ASCII machines, but is |
87 | UTF-EBCDIC on EBCDIC machines.) This allows any character perl can |
88 | represent to be read from or written to the stream. The UTF-X encoding |
89 | is chosen to render simple text parts (i.e. non-accented letters, |
90 | digits and common punctuation) human readable in the encoded file. |
91 | |
92 | Here is how to write your native data out using UTF-8 (or UTF-EBCDIC) |
93 | and then read it back in. |
94 | |
95 | open(F, ">:utf8", "data.utf"); |
96 | print F $out; |
97 | close(F); |
98 | |
99 | open(F, "<:utf8", "data.utf"); |
100 | $in = <F>; |
101 | close(F); |
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102 | |
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103 | =item bytes |
104 | |
105 | This is the inverse of C<:utf8> layer. It turns off the flag |
106 | on the layer below so that data read from it is considered to |
107 | be "octets" i.e. characters in range 0..255 only. Likewise |
108 | on output perl will warn if a "wide" character is written |
109 | to a such a stream. |
110 | |
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111 | =item raw |
112 | |
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113 | B<Note that the explicit use of the C<raw> layer is deprecated.> |
114 | |
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115 | A pseudo-layer which performs two functions (which is messy, but |
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116 | necessary to maintain compatibility with non-PerlIO builds of Perl |
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117 | and their way things have been documented elsewhere). |
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118 | |
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119 | Firstly it forces the file handle to be considered binary at that |
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120 | point in the layer stack, i.e. it turns off any CRLF translation. |
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121 | |
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122 | Secondly in prevents the IO system seaching back before it in the |
123 | layer specification. Thus: |
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124 | |
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125 | open($fh,":raw:perlio",...) |
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126 | |
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127 | Forces the use of C<perlio> layer even if the platform default, or |
128 | C<use open> default is something else (such as ":encoding(iso-8859-7)") |
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129 | (the C<:encoding> requires C<use Encode>) which would interfere with |
130 | binary nature of the stream. |
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131 | |
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132 | =back |
133 | |
134 | =head2 Defaults and how to override them |
135 | |
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136 | If the platform is MS-DOS like and normally does CRLF to "\n" |
137 | translation for text files then the default layers are : |
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138 | |
139 | unix crlf |
140 | |
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141 | (The low level "unix" layer may be replaced by a platform specific low |
142 | level layer.) |
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143 | |
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144 | Otherwise if C<Configure> found out how to do "fast" IO using system's |
145 | stdio, then the default layers are : |
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146 | |
147 | unix stdio |
148 | |
149 | Otherwise the default layers are |
150 | |
151 | unix perlio |
152 | |
153 | These defaults may change once perlio has been better tested and tuned. |
154 | |
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155 | The default can be overridden by setting the environment variable |
156 | PERLIO to a space separated list of layers (unix or platform low level |
157 | layer is always pushed first). |
158 | |
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159 | This can be used to see the effect of/bugs in the various layers e.g. |
160 | |
161 | cd .../perl/t |
162 | PERLIO=stdio ./perl harness |
163 | PERLIO=perlio ./perl harness |
164 | |
165 | =head1 AUTHOR |
166 | |
167 | Nick Ing-Simmons E<lt>nick@ing-simmons.netE<gt> |
168 | |
169 | =head1 SEE ALSO |
170 | |
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171 | L<perlfunc/"binmode">, L<perlfunc/"open">, L<perlunicode>, L<Encode> |
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172 | |
173 | =cut |
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174 | |