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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 | |
42 | When an undefined layer 'foo' is encountered in an C<open> or C<binmode> layer |
43 | specification then C code performs the equivalent of: |
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 | |
51 | Otherwise the C<PerlIO> package is a place holder for additional PerLIO related |
52 | functions. |
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 | |
64 | Layer which calls C<fread>, C<fwrite> and C<fseek>/C<ftell> etc. |
65 | Note that as this is "real" stdio it will ignore any layers beneath it and |
66 | got straight to the operating system via the C library as usual. |
67 | |
68 | =item perlio |
69 | |
70 | This is a re-implementation of "stdio-like" buffering written as a PerlIO "layer". |
71 | As such it will call whatever layer is below it for its operations. |
72 | |
73 | =item crlf |
74 | |
75 | A layer which does CRLF to "\n" translation distinguishing "text" and "binary" |
76 | files in the manner of MS-DOS and similar operating systems. |
77 | |
78 | =item utf8 |
79 | |
80 | Declares that the stream accepts perl's internal encoding of characters. |
81 | (Which really is UTF-8 on ASCII machines, but is UTF-EBCDIC on EBCDIC machines.) |
82 | This allows any character perl can represent to be read from or written to the |
83 | stream. The UTF-X encoding is chosen to render simple text parts (i.e. |
84 | non-accented letters, digits and common punctuation) human readable in the |
85 | encoded file. |
86 | |
87 | =item raw |
88 | |
89 | A pseudo-layer which performs two functions (which is messy, but necessary to |
90 | maintain compatibility with non-PerLIO builds of perl and they way things |
91 | have been documented elsewhere). |
92 | |
93 | Firstly it forces the file handle to be considered binary at that point |
94 | in the layer stack, |
95 | |
96 | Secondly in prevents the IO system seaching back before it in the layer specification. |
97 | Thus: |
98 | |
99 | open($fh,":raw:perlio"),...) |
100 | |
101 | Forces the use of C<perlio> layer even if the platform default, or C<use open> default |
102 | is something else (such as ":encoding(iso-8859-7)" ) which would interfere with |
103 | binary nature of the stream. |
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104 | |
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105 | =back |
106 | |
107 | =head2 Defaults and how to override them |
108 | |
109 | If the platform is MS-DOS like and normally does CRLF to "\n" translation |
110 | for text files then the default layers are : |
111 | |
112 | unix crlf |
113 | |
114 | (The low level "unix" layer may be replaced by a platform specific low level layer.) |
115 | |
116 | Otherwise if C<Configure> found out how to do "fast" IO using system's stdio, then |
117 | the default layers are : |
118 | |
119 | unix stdio |
120 | |
121 | Otherwise the default layers are |
122 | |
123 | unix perlio |
124 | |
125 | These defaults may change once perlio has been better tested and tuned. |
126 | |
127 | The default can be overridden by setting the environment variable PERLIO |
128 | to a space separated list of layers (unix or platform low level layer is |
129 | always pushed first). |
130 | This can be used to see the effect of/bugs in the various layers e.g. |
131 | |
132 | cd .../perl/t |
133 | PERLIO=stdio ./perl harness |
134 | PERLIO=perlio ./perl harness |
135 | |
136 | =head1 AUTHOR |
137 | |
138 | Nick Ing-Simmons E<lt>nick@ing-simmons.netE<gt> |
139 | |
140 | =head1 SEE ALSO |
141 | |
142 | L<perlfunc/"binmode">, L<perlfunc/"open">, L<perlunicode>, L<open> |
143 | |
144 | =cut |
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145 | |