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1141d9f8 NIS |
1 | package PerlIO; |
2 | ||
c1a61b17 | 3 | our $VERSION = '1.01'; |
8de1277c | 4 | |
1141d9f8 | 5 | # Map layer name to package that defines it |
c1a61b17 | 6 | our %alias; |
1141d9f8 NIS |
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 $@; | |
24 | } | |
25 | } | |
26 | ||
27 | 1; | |
28 | __END__ | |
b3d30bf7 NIS |
29 | |
30 | =head1 NAME | |
31 | ||
7d3b96bb | 32 | PerlIO - On demand loader for PerlIO layers and root of PerlIO::* name space |
b3d30bf7 NIS |
33 | |
34 | =head1 SYNOPSIS | |
35 | ||
7d3b96bb NIS |
36 | open($fh,">:crlf","my.txt") |
37 | open($fh,">:raw","his.jpg") | |
38 | ||
39 | Shell: | |
40 | PERLIO=perlio perl .... | |
b3d30bf7 NIS |
41 | |
42 | =head1 DESCRIPTION | |
43 | ||
ec28694c JH |
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: | |
b3d30bf7 NIS |
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 | ||
47bfe92f JH |
53 | Otherwise the C<PerlIO> package is a place holder for additional |
54 | PerlIO related functions. | |
b3d30bf7 | 55 | |
7d3b96bb | 56 | The following layers are currently defined: |
b3d30bf7 | 57 | |
7d3b96bb NIS |
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 | ||
47bfe92f JH |
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 | |
7d3b96bb NIS |
68 | got straight to the operating system via the C library as usual. |
69 | ||
70 | =item perlio | |
71 | ||
47bfe92f JH |
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. | |
7d3b96bb NIS |
75 | |
76 | =item crlf | |
77 | ||
47bfe92f JH |
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. | |
7d3b96bb NIS |
80 | |
81 | =item utf8 | |
82 | ||
47bfe92f JH |
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 | $in = <F>; | |
99 | close(F); | |
7d3b96bb | 100 | |
c1a61b17 NIS |
101 | =item bytes |
102 | ||
103 | This is the inverse of C<:utf8> layer. It turns off the flag | |
104 | on the layer below so that data read from it is considered to | |
105 | be "octets" i.e. characters in range 0..255 only. Likewise | |
106 | on output perl will warn if a "wide" character is written | |
107 | to a such a stream. | |
108 | ||
7d3b96bb NIS |
109 | =item raw |
110 | ||
47bfe92f | 111 | A pseudo-layer which performs two functions (which is messy, but |
ec28694c | 112 | necessary to maintain compatibility with non-PerlIO builds of Perl |
47bfe92f | 113 | and their way things have been documented elsewhere). |
7d3b96bb | 114 | |
47bfe92f | 115 | Firstly it forces the file handle to be considered binary at that |
c1a61b17 | 116 | point in the layer stack, i.e. it turns off any CRLF translation. |
7d3b96bb | 117 | |
47bfe92f JH |
118 | Secondly in prevents the IO system seaching back before it in the |
119 | layer specification. Thus: | |
7d3b96bb | 120 | |
47bfe92f | 121 | open($fh,":raw:perlio",...) |
7d3b96bb | 122 | |
47bfe92f JH |
123 | Forces the use of C<perlio> layer even if the platform default, or |
124 | C<use open> default is something else (such as ":encoding(iso-8859-7)") | |
42234700 JH |
125 | (the C<:encoding> requires C<use Encode>) which would interfere with |
126 | binary nature of the stream. | |
b3d30bf7 | 127 | |
7d3b96bb NIS |
128 | =back |
129 | ||
130 | =head2 Defaults and how to override them | |
131 | ||
ec28694c JH |
132 | If the platform is MS-DOS like and normally does CRLF to "\n" |
133 | translation for text files then the default layers are : | |
7d3b96bb NIS |
134 | |
135 | unix crlf | |
136 | ||
47bfe92f JH |
137 | (The low level "unix" layer may be replaced by a platform specific low |
138 | level layer.) | |
7d3b96bb | 139 | |
47bfe92f JH |
140 | Otherwise if C<Configure> found out how to do "fast" IO using system's |
141 | stdio, then the default layers are : | |
7d3b96bb NIS |
142 | |
143 | unix stdio | |
144 | ||
145 | Otherwise the default layers are | |
146 | ||
147 | unix perlio | |
148 | ||
149 | These defaults may change once perlio has been better tested and tuned. | |
150 | ||
47bfe92f JH |
151 | The default can be overridden by setting the environment variable |
152 | PERLIO to a space separated list of layers (unix or platform low level | |
153 | layer is always pushed first). | |
154 | ||
7d3b96bb NIS |
155 | This can be used to see the effect of/bugs in the various layers e.g. |
156 | ||
157 | cd .../perl/t | |
158 | PERLIO=stdio ./perl harness | |
159 | PERLIO=perlio ./perl harness | |
160 | ||
161 | =head1 AUTHOR | |
162 | ||
163 | Nick Ing-Simmons E<lt>nick@ing-simmons.netE<gt> | |
164 | ||
165 | =head1 SEE ALSO | |
166 | ||
47bfe92f | 167 | L<perlfunc/"binmode">, L<perlfunc/"open">, L<perlunicode>, L<Encode> |
7d3b96bb NIS |
168 | |
169 | =cut | |
b3d30bf7 | 170 |