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1141d9f8 NIS |
1 | package PerlIO; |
2 | ||
22a7fd7a | 3 | our $VERSION = '1.04'; |
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 $@; | |
24 | } | |
25 | } | |
26 | ||
39f7a870 JH |
27 | sub F_UTF8 () { 0x8000 } |
28 | ||
1141d9f8 NIS |
29 | 1; |
30 | __END__ | |
b3d30bf7 NIS |
31 | |
32 | =head1 NAME | |
33 | ||
7d3b96bb | 34 | PerlIO - On demand loader for PerlIO layers and root of PerlIO::* name space |
b3d30bf7 NIS |
35 | |
36 | =head1 SYNOPSIS | |
37 | ||
a7845df8 | 38 | open($fh,"<:crlf", "my.txt"); # support platform-native and CRLF text files |
1cbfc93d NIS |
39 | |
40 | open($fh,"<","his.jpg"); # portably open a binary file for reading | |
41 | binmode($fh); | |
7d3b96bb NIS |
42 | |
43 | Shell: | |
44 | PERLIO=perlio perl .... | |
b3d30bf7 NIS |
45 | |
46 | =head1 DESCRIPTION | |
47 | ||
ec28694c JH |
48 | When an undefined layer 'foo' is encountered in an C<open> or |
49 | C<binmode> layer specification then C code performs the equivalent of: | |
b3d30bf7 NIS |
50 | |
51 | use PerlIO 'foo'; | |
52 | ||
53 | The perl code in PerlIO.pm then attempts to locate a layer by doing | |
54 | ||
55 | require PerlIO::foo; | |
56 | ||
47bfe92f JH |
57 | Otherwise the C<PerlIO> package is a place holder for additional |
58 | PerlIO related functions. | |
b3d30bf7 | 59 | |
7d3b96bb | 60 | The following layers are currently defined: |
b3d30bf7 | 61 | |
7d3b96bb NIS |
62 | =over 4 |
63 | ||
3d897973 | 64 | =item :unix |
7d3b96bb | 65 | |
3d897973 IT |
66 | Lowest level layer which provides basic PerlIO operations in terms of |
67 | UNIX/POSIX numeric file descriptor calls | |
68 | (open(), read(), write(), lseek(), close()). | |
7d3b96bb | 69 | |
3d897973 | 70 | =item :stdio |
7d3b96bb | 71 | |
47bfe92f JH |
72 | Layer which calls C<fread>, C<fwrite> and C<fseek>/C<ftell> etc. Note |
73 | that as this is "real" stdio it will ignore any layers beneath it and | |
7d3b96bb NIS |
74 | got straight to the operating system via the C library as usual. |
75 | ||
3d897973 | 76 | =item :perlio |
7d3b96bb | 77 | |
3d897973 IT |
78 | A from scratch implementation of buffering for PerlIO. Provides fast |
79 | access to the buffer for C<sv_gets> which implements perl's readline/E<lt>E<gt> | |
80 | and in general attempts to minimize data copying. | |
7d3b96bb | 81 | |
3d897973 | 82 | C<:perlio> will insert a C<:unix> layer below itself to do low level IO. |
7d3b96bb | 83 | |
3d897973 | 84 | =item :crlf |
7d3b96bb | 85 | |
3d897973 IT |
86 | A layer that implements DOS/Windows like CRLF line endings. On read |
87 | converts pairs of CR,LF to a single "\n" newline character. On write | |
88 | converts each "\n" to a CR,LF pair. Note that this layer likes to be | |
89 | one of its kind: it silently ignores attempts to be pushed into the | |
90 | layer stack more than once. | |
91 | ||
92 | It currently does I<not> mimic MS-DOS as far as treating of Control-Z | |
93 | as being an end-of-file marker. | |
94 | ||
95 | (Gory details follow) To be more exact what happens is this: after | |
96 | pushing itself to the stack, the C<:crlf> layer checks all the layers | |
97 | below itself to find the first layer that is capable of being a CRLF | |
98 | layer but is not yet enabled to be a CRLF layer. If it finds such a | |
99 | layer, it enables the CRLFness of that other deeper layer, and then | |
100 | pops itself off the stack. If not, fine, use the one we just pushed. | |
101 | ||
102 | The end result is that a C<:crlf> means "please enable the first CRLF | |
103 | layer you can find, and if you can't find one, here would be a good | |
104 | spot to place a new one." | |
105 | ||
106 | Based on the C<:perlio> layer. | |
107 | ||
108 | =item :mmap | |
109 | ||
110 | A layer which implements "reading" of files by using C<mmap()> to | |
111 | make (whole) file appear in the process's address space, and then | |
112 | using that as PerlIO's "buffer". This I<may> be faster in certain | |
113 | circumstances for large files, and may result in less physical memory | |
114 | use when multiple processes are reading the same file. | |
115 | ||
116 | Files which are not C<mmap()>-able revert to behaving like the C<:perlio> | |
117 | layer. Writes also behave like C<:perlio> layer as C<mmap()> for write | |
118 | needs extra house-keeping (to extend the file) which negates any advantage. | |
119 | ||
120 | The C<:mmap> layer will not exist if platform does not support C<mmap()>. | |
121 | ||
122 | =item :utf8 | |
7d3b96bb | 123 | |
47bfe92f JH |
124 | Declares that the stream accepts perl's internal encoding of |
125 | characters. (Which really is UTF-8 on ASCII machines, but is | |
126 | UTF-EBCDIC on EBCDIC machines.) This allows any character perl can | |
127 | represent to be read from or written to the stream. The UTF-X encoding | |
128 | is chosen to render simple text parts (i.e. non-accented letters, | |
129 | digits and common punctuation) human readable in the encoded file. | |
130 | ||
131 | Here is how to write your native data out using UTF-8 (or UTF-EBCDIC) | |
132 | and then read it back in. | |
133 | ||
134 | open(F, ">:utf8", "data.utf"); | |
135 | print F $out; | |
136 | close(F); | |
137 | ||
138 | open(F, "<:utf8", "data.utf"); | |
139 | $in = <F>; | |
140 | close(F); | |
7d3b96bb | 141 | |
3d897973 | 142 | =item :bytes |
c1a61b17 NIS |
143 | |
144 | This is the inverse of C<:utf8> layer. It turns off the flag | |
145 | on the layer below so that data read from it is considered to | |
146 | be "octets" i.e. characters in range 0..255 only. Likewise | |
147 | on output perl will warn if a "wide" character is written | |
148 | to a such a stream. | |
149 | ||
3d897973 | 150 | =item :raw |
7d3b96bb | 151 | |
0226bbdb | 152 | The C<:raw> layer is I<defined> as being identical to calling |
18aba96f JH |
153 | C<binmode($fh)> - the stream is made suitable for passing binary data |
154 | i.e. each byte is passed as-is. The stream will still be | |
3d897973 IT |
155 | buffered. |
156 | ||
157 | In Perl 5.6 and some books the C<:raw> layer (previously sometimes also | |
158 | referred to as a "discipline") is documented as the inverse of the | |
159 | C<:crlf> layer. That is no longer the case - other layers which would | |
160 | alter binary nature of the stream are also disabled. If you want UNIX | |
161 | line endings on a platform that normally does CRLF translation, but still | |
162 | want UTF-8 or encoding defaults the appropriate thing to do is to add | |
163 | C<:perlio> to PERLIO environment variable. | |
1cbfc93d | 164 | |
0226bbdb NIS |
165 | The implementation of C<:raw> is as a pseudo-layer which when "pushed" |
166 | pops itself and then any layers which do not declare themselves as suitable | |
167 | for binary data. (Undoing :utf8 and :crlf are implemented by clearing | |
39f7a870 | 168 | flags rather than popping layers but that is an implementation detail.) |
01e6739c | 169 | |
0226bbdb | 170 | As a consequence of the fact that C<:raw> normally pops layers |
39f7a870 JH |
171 | it usually only makes sense to have it as the only or first element in |
172 | a layer specification. When used as the first element it provides | |
0226bbdb | 173 | a known base on which to build e.g. |
7d3b96bb | 174 | |
0226bbdb | 175 | open($fh,":raw:utf8",...) |
7d3b96bb | 176 | |
0226bbdb | 177 | will construct a "binary" stream, but then enable UTF-8 translation. |
b3d30bf7 | 178 | |
3d897973 | 179 | =item :pop |
4ec2216f NIS |
180 | |
181 | A pseudo layer that removes the top-most layer. Gives perl code | |
182 | a way to manipulate the layer stack. Should be considered | |
183 | as experimental. Note that C<:pop> only works on real layers | |
184 | and will not undo the effects of pseudo layers like C<:utf8>. | |
185 | An example of a possible use might be: | |
186 | ||
187 | open($fh,...) | |
188 | ... | |
189 | binmode($fh,":encoding(...)"); # next chunk is encoded | |
190 | ... | |
3c4b39be | 191 | binmode($fh,":pop"); # back to un-encoded |
4ec2216f NIS |
192 | |
193 | A more elegant (and safer) interface is needed. | |
194 | ||
3d897973 IT |
195 | =item :win32 |
196 | ||
197 | On Win32 platforms this I<experimental> layer uses native "handle" IO | |
198 | rather than unix-like numeric file descriptor layer. Known to be | |
199 | buggy as of perl 5.8.2. | |
200 | ||
7d3b96bb NIS |
201 | =back |
202 | ||
39f7a870 JH |
203 | =head2 Custom Layers |
204 | ||
205 | It is possible to write custom layers in addition to the above builtin | |
206 | ones, both in C/XS and Perl. Two such layers (and one example written | |
207 | in Perl using the latter) come with the Perl distribution. | |
208 | ||
209 | =over 4 | |
210 | ||
211 | =item :encoding | |
212 | ||
213 | Use C<:encoding(ENCODING)> either in open() or binmode() to install | |
214 | a layer that does transparently character set and encoding transformations, | |
e76300d6 JH |
215 | for example from Shift-JIS to Unicode. Note that under C<stdio> |
216 | an C<:encoding> also enables C<:utf8>. See L<PerlIO::encoding> | |
217 | for more information. | |
39f7a870 JH |
218 | |
219 | =item :via | |
220 | ||
221 | Use C<:via(MODULE)> either in open() or binmode() to install a layer | |
222 | that does whatever transformation (for example compression / | |
223 | decompression, encryption / decryption) to the filehandle. | |
224 | See L<PerlIO::via> for more information. | |
225 | ||
226 | =back | |
227 | ||
01e6739c NIS |
228 | =head2 Alternatives to raw |
229 | ||
0226bbdb | 230 | To get a binary stream an alternate method is to use: |
01e6739c | 231 | |
0226bbdb | 232 | open($fh,"whatever") |
01e6739c NIS |
233 | binmode($fh); |
234 | ||
0226bbdb | 235 | this has advantage of being backward compatible with how such things have |
01e6739c | 236 | had to be coded on some platforms for years. |
01e6739c NIS |
237 | |
238 | To get an un-buffered stream specify an unbuffered layer (e.g. C<:unix>) | |
0226bbdb | 239 | in the open call: |
01e6739c NIS |
240 | |
241 | open($fh,"<:unix",$path) | |
242 | ||
7d3b96bb NIS |
243 | =head2 Defaults and how to override them |
244 | ||
ec28694c JH |
245 | If the platform is MS-DOS like and normally does CRLF to "\n" |
246 | translation for text files then the default layers are : | |
7d3b96bb NIS |
247 | |
248 | unix crlf | |
249 | ||
47bfe92f JH |
250 | (The low level "unix" layer may be replaced by a platform specific low |
251 | level layer.) | |
7d3b96bb | 252 | |
47bfe92f | 253 | Otherwise if C<Configure> found out how to do "fast" IO using system's |
046e4a6a | 254 | stdio, then the default layers are: |
7d3b96bb NIS |
255 | |
256 | unix stdio | |
257 | ||
258 | Otherwise the default layers are | |
259 | ||
260 | unix perlio | |
261 | ||
262 | These defaults may change once perlio has been better tested and tuned. | |
263 | ||
47bfe92f | 264 | The default can be overridden by setting the environment variable |
39f7a870 JH |
265 | PERLIO to a space separated list of layers (C<unix> or platform low |
266 | level layer is always pushed first). | |
47bfe92f | 267 | |
7d3b96bb NIS |
268 | This can be used to see the effect of/bugs in the various layers e.g. |
269 | ||
270 | cd .../perl/t | |
271 | PERLIO=stdio ./perl harness | |
272 | PERLIO=perlio ./perl harness | |
273 | ||
3b0db4f9 JH |
274 | For the various value of PERLIO see L<perlrun/PERLIO>. |
275 | ||
4c11337c | 276 | =head2 Querying the layers of filehandles |
39f7a870 JH |
277 | |
278 | The following returns the B<names> of the PerlIO layers on a filehandle. | |
279 | ||
9d569fce | 280 | my @layers = PerlIO::get_layers($fh); # Or FH, *FH, "FH". |
39f7a870 JH |
281 | |
282 | The layers are returned in the order an open() or binmode() call would | |
f0fd62e2 | 283 | use them. Note that the "default stack" depends on the operating |
cc83745d JH |
284 | system and on the Perl version, and both the compile-time and |
285 | runtime configurations of Perl. | |
79d9a4d7 | 286 | |
79d9a4d7 JH |
287 | The following table summarizes the default layers on UNIX-like and |
288 | DOS-like platforms and depending on the setting of the C<$ENV{PERLIO}>: | |
289 | ||
f0fd62e2 | 290 | PERLIO UNIX-like DOS-like |
a7845df8 | 291 | ------ --------- -------- |
f0fd62e2 JH |
292 | unset / "" unix perlio / stdio [1] unix crlf |
293 | stdio unix perlio / stdio [1] stdio | |
294 | perlio unix perlio unix perlio | |
295 | mmap unix mmap unix mmap | |
39f7a870 | 296 | |
f0fd62e2 JH |
297 | # [1] "stdio" if Configure found out how to do "fast stdio" (depends |
298 | # on the stdio implementation) and in Perl 5.8, otherwise "unix perlio" | |
046e4a6a | 299 | |
39f7a870 JH |
300 | By default the layers from the input side of the filehandle is |
301 | returned, to get the output side use the optional C<output> argument: | |
302 | ||
2ae85e59 | 303 | my @layers = PerlIO::get_layers($fh, output => 1); |
39f7a870 JH |
304 | |
305 | (Usually the layers are identical on either side of a filehandle but | |
2ae85e59 JH |
306 | for example with sockets there may be differences, or if you have |
307 | been using the C<open> pragma.) | |
39f7a870 | 308 | |
92a3e63c JH |
309 | There is no set_layers(), nor does get_layers() return a tied array |
310 | mirroring the stack, or anything fancy like that. This is not | |
311 | accidental or unintentional. The PerlIO layer stack is a bit more | |
312 | complicated than just a stack (see for example the behaviour of C<:raw>). | |
313 | You are supposed to use open() and binmode() to manipulate the stack. | |
314 | ||
39f7a870 JH |
315 | B<Implementation details follow, please close your eyes.> |
316 | ||
317 | The arguments to layers are by default returned in parenthesis after | |
318 | the name of the layer, and certain layers (like C<utf8>) are not real | |
319 | layers but instead flags on real layers: to get all of these returned | |
6cd4dd6c | 320 | separately use the optional C<details> argument: |
39f7a870 | 321 | |
2ae85e59 | 322 | my @layer_and_args_and_flags = PerlIO::get_layers($fh, details => 1); |
39f7a870 JH |
323 | |
324 | The result will be up to be three times the number of layers: | |
325 | the first element will be a name, the second element the arguments | |
326 | (unspecified arguments will be C<undef>), the third element the flags, | |
327 | the fourth element a name again, and so forth. | |
328 | ||
329 | B<You may open your eyes now.> | |
330 | ||
7d3b96bb NIS |
331 | =head1 AUTHOR |
332 | ||
333 | Nick Ing-Simmons E<lt>nick@ing-simmons.netE<gt> | |
334 | ||
335 | =head1 SEE ALSO | |
336 | ||
39f7a870 JH |
337 | L<perlfunc/"binmode">, L<perlfunc/"open">, L<perlunicode>, L<perliol>, |
338 | L<Encode> | |
7d3b96bb NIS |
339 | |
340 | =cut |