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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 reading |
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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 | (It currently does I<not> mimic MS-DOS as far as treating of Control-Z |
83 | as being an end-of-file marker.) |
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84 | |
85 | =item utf8 |
86 | |
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87 | Declares that the stream accepts perl's internal encoding of |
88 | characters. (Which really is UTF-8 on ASCII machines, but is |
89 | UTF-EBCDIC on EBCDIC machines.) This allows any character perl can |
90 | represent to be read from or written to the stream. The UTF-X encoding |
91 | is chosen to render simple text parts (i.e. non-accented letters, |
92 | digits and common punctuation) human readable in the encoded file. |
93 | |
94 | Here is how to write your native data out using UTF-8 (or UTF-EBCDIC) |
95 | and then read it back in. |
96 | |
97 | open(F, ">:utf8", "data.utf"); |
98 | print F $out; |
99 | close(F); |
100 | |
101 | open(F, "<:utf8", "data.utf"); |
102 | $in = <F>; |
103 | close(F); |
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104 | |
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105 | =item bytes |
106 | |
107 | This is the inverse of C<:utf8> layer. It turns off the flag |
108 | on the layer below so that data read from it is considered to |
109 | be "octets" i.e. characters in range 0..255 only. Likewise |
110 | on output perl will warn if a "wide" character is written |
111 | to a such a stream. |
112 | |
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113 | =item raw |
114 | |
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115 | The C<:raw> layer is I<defined> as being identical to calling |
116 | C<binmode($fh)> - the stream is made suitable for passing binary |
117 | data i.e. each byte is passed as-is. The stream will still be |
118 | buffered. Unlike earlier versions of perl C<:raw> is I<not> just the |
119 | inverse of C<:crlf> - other layers which would affect the binary nature of |
120 | the stream are also removed or disabled. |
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121 | |
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122 | The implementation of C<:raw> is as a pseudo-layer which when "pushed" |
123 | pops itself and then any layers which do not declare themselves as suitable |
124 | for binary data. (Undoing :utf8 and :crlf are implemented by clearing |
125 | flags rather than poping layers but that is an implementation detail.) |
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126 | |
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127 | As a consequence of the fact that C<:raw> normally pops layers |
128 | it usually only makes sense to have it as the only or first element in a |
129 | layer specification. When used as the first element it provides |
130 | a known base on which to build e.g. |
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131 | |
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132 | open($fh,":raw:utf8",...) |
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133 | |
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134 | will construct a "binary" stream, but then enable UTF-8 translation. |
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135 | |
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136 | =item pop |
137 | |
138 | A pseudo layer that removes the top-most layer. Gives perl code |
139 | a way to manipulate the layer stack. Should be considered |
140 | as experimental. Note that C<:pop> only works on real layers |
141 | and will not undo the effects of pseudo layers like C<:utf8>. |
142 | An example of a possible use might be: |
143 | |
144 | open($fh,...) |
145 | ... |
146 | binmode($fh,":encoding(...)"); # next chunk is encoded |
147 | ... |
148 | binmode($fh,":pop"); # back to un-encocded |
149 | |
150 | A more elegant (and safer) interface is needed. |
151 | |
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152 | =back |
153 | |
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154 | =head2 Alternatives to raw |
155 | |
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156 | To get a binary stream an alternate method is to use: |
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157 | |
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158 | open($fh,"whatever") |
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159 | binmode($fh); |
160 | |
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161 | this has advantage of being backward compatible with how such things have |
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162 | had to be coded on some platforms for years. |
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163 | |
164 | To get an un-buffered stream specify an unbuffered layer (e.g. C<:unix>) |
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165 | in the open call: |
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166 | |
167 | open($fh,"<:unix",$path) |
168 | |
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169 | =head2 Defaults and how to override them |
170 | |
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171 | If the platform is MS-DOS like and normally does CRLF to "\n" |
172 | translation for text files then the default layers are : |
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173 | |
174 | unix crlf |
175 | |
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176 | (The low level "unix" layer may be replaced by a platform specific low |
177 | level layer.) |
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178 | |
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179 | Otherwise if C<Configure> found out how to do "fast" IO using system's |
180 | stdio, then the default layers are : |
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181 | |
182 | unix stdio |
183 | |
184 | Otherwise the default layers are |
185 | |
186 | unix perlio |
187 | |
188 | These defaults may change once perlio has been better tested and tuned. |
189 | |
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190 | The default can be overridden by setting the environment variable |
191 | PERLIO to a space separated list of layers (unix or platform low level |
192 | layer is always pushed first). |
193 | |
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194 | This can be used to see the effect of/bugs in the various layers e.g. |
195 | |
196 | cd .../perl/t |
197 | PERLIO=stdio ./perl harness |
198 | PERLIO=perlio ./perl harness |
199 | |
200 | =head1 AUTHOR |
201 | |
202 | Nick Ing-Simmons E<lt>nick@ing-simmons.netE<gt> |
203 | |
204 | =head1 SEE ALSO |
205 | |
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206 | L<perlfunc/"binmode">, L<perlfunc/"open">, L<perlunicode>, L<perliol>, L<Encode> |
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207 | |
208 | =cut |
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209 | |