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129 | .\" ======================================================================== | |
130 | .\" | |
131 | .IX Title "open 3" | |
132 | .TH open 3 "2001-09-21" "perl v5.8.8" "Perl Programmers Reference Guide" | |
133 | .SH "NAME" | |
134 | open \- perl pragma to set default PerlIO layers for input and output | |
135 | .SH "SYNOPSIS" | |
136 | .IX Header "SYNOPSIS" | |
137 | .Vb 3 | |
138 | \& use open IN => ":crlf", OUT => ":bytes"; | |
139 | \& use open OUT => ':utf8'; | |
140 | \& use open IO => ":encoding(iso-8859-7)"; | |
141 | .Ve | |
142 | .PP | |
143 | .Vb 1 | |
144 | \& use open IO => ':locale'; | |
145 | .Ve | |
146 | .PP | |
147 | .Vb 3 | |
148 | \& use open ':utf8'; | |
149 | \& use open ':locale'; | |
150 | \& use open ':encoding(iso-8859-7)'; | |
151 | .Ve | |
152 | .PP | |
153 | .Vb 1 | |
154 | \& use open ':std'; | |
155 | .Ve | |
156 | .SH "DESCRIPTION" | |
157 | .IX Header "DESCRIPTION" | |
158 | Full-fledged support for I/O layers is now implemented provided | |
159 | Perl is configured to use PerlIO as its \s-1IO\s0 system (which is now the | |
160 | default). | |
161 | .PP | |
162 | The \f(CW\*(C`open\*(C'\fR pragma serves as one of the interfaces to declare default | |
163 | \&\*(L"layers\*(R" (also known as \*(L"disciplines\*(R") for all I/O. Any two-argument | |
164 | \&\fIopen()\fR, \fIreadpipe()\fR (aka qx//) and similar operators found within the | |
165 | lexical scope of this pragma will use the declared defaults. | |
166 | Even three-argument opens may be affected by this pragma | |
167 | when they don't specify \s-1IO\s0 layers in \s-1MODE\s0. | |
168 | .PP | |
169 | With the \f(CW\*(C`IN\*(C'\fR subpragma you can declare the default layers | |
170 | of input streams, and with the \f(CW\*(C`OUT\*(C'\fR subpragma you can declare | |
171 | the default layers of output streams. With the \f(CW\*(C`IO\*(C'\fR subpragma | |
172 | you can control both input and output streams simultaneously. | |
173 | .PP | |
174 | If you have a legacy encoding, you can use the \f(CW\*(C`:encoding(...)\*(C'\fR tag. | |
175 | .PP | |
176 | If you want to set your encoding layers based on your | |
177 | locale environment variables, you can use the \f(CW\*(C`:locale\*(C'\fR tag. | |
178 | For example: | |
179 | .PP | |
180 | .Vb 9 | |
181 | \& $ENV{LANG} = 'ru_RU.KOI8-R'; | |
182 | \& # the :locale will probe the locale environment variables like LANG | |
183 | \& use open OUT => ':locale'; | |
184 | \& open(O, ">koi8"); | |
185 | \& print O chr(0x430); # Unicode CYRILLIC SMALL LETTER A = KOI8-R 0xc1 | |
186 | \& close O; | |
187 | \& open(I, "<koi8"); | |
188 | \& printf "%#x\en", ord(<I>), "\en"; # this should print 0xc1 | |
189 | \& close I; | |
190 | .Ve | |
191 | .PP | |
192 | These are equivalent | |
193 | .PP | |
194 | .Vb 2 | |
195 | \& use open ':utf8'; | |
196 | \& use open IO => ':utf8'; | |
197 | .Ve | |
198 | .PP | |
199 | as are these | |
200 | .PP | |
201 | .Vb 2 | |
202 | \& use open ':locale'; | |
203 | \& use open IO => ':locale'; | |
204 | .Ve | |
205 | .PP | |
206 | and these | |
207 | .PP | |
208 | .Vb 2 | |
209 | \& use open ':encoding(iso-8859-7)'; | |
210 | \& use open IO => ':encoding(iso-8859-7)'; | |
211 | .Ve | |
212 | .PP | |
213 | The matching of encoding names is loose: case does not matter, and | |
214 | many encodings have several aliases. See Encode::Supported for | |
215 | details and the list of supported locales. | |
216 | .PP | |
217 | Note that \f(CW\*(C`:utf8\*(C'\fR PerlIO layer must always be specified exactly like | |
218 | that, it is not subject to the loose matching of encoding names. | |
219 | .PP | |
220 | When \fIopen()\fR is given an explicit list of layers (with the three-arg | |
221 | syntax), they override the list declared using this pragma. | |
222 | .PP | |
223 | The \f(CW\*(C`:std\*(C'\fR subpragma on its own has no effect, but if combined with | |
224 | the \f(CW\*(C`:utf8\*(C'\fR or \f(CW\*(C`:encoding\*(C'\fR subpragmas, it converts the standard | |
225 | filehandles (\s-1STDIN\s0, \s-1STDOUT\s0, \s-1STDERR\s0) to comply with encoding selected | |
226 | for input/output handles. For example, if both input and out are | |
227 | chosen to be \f(CW\*(C`:utf8\*(C'\fR, a \f(CW\*(C`:std\*(C'\fR will mean that \s-1STDIN\s0, \s-1STDOUT\s0, and | |
228 | \&\s-1STDERR\s0 are also in \f(CW\*(C`:utf8\*(C'\fR. On the other hand, if only output is | |
229 | chosen to be in \f(CW\*(C`:encoding(koi8r)\*(C'\fR, a \f(CW\*(C`:std\*(C'\fR will cause only the | |
230 | \&\s-1STDOUT\s0 and \s-1STDERR\s0 to be in \f(CW\*(C`koi8r\*(C'\fR. The \f(CW\*(C`:locale\*(C'\fR subpragma | |
231 | implicitly turns on \f(CW\*(C`:std\*(C'\fR. | |
232 | .PP | |
233 | The logic of \f(CW\*(C`:locale\*(C'\fR is described in full in encoding, | |
234 | but in short it is first trying nl_langinfo(\s-1CODESET\s0) and then | |
235 | guessing from the \s-1LC_ALL\s0 and \s-1LANG\s0 locale environment variables. | |
236 | .PP | |
237 | Directory handles may also support PerlIO layers in the future. | |
238 | .SH "NONPERLIO FUNCTIONALITY" | |
239 | .IX Header "NONPERLIO FUNCTIONALITY" | |
240 | If Perl is not built to use PerlIO as its \s-1IO\s0 system then only the two | |
241 | pseudo-layers \f(CW\*(C`:bytes\*(C'\fR and \f(CW\*(C`:crlf\*(C'\fR are available. | |
242 | .PP | |
243 | The \f(CW\*(C`:bytes\*(C'\fR layer corresponds to \*(L"binary mode\*(R" and the \f(CW\*(C`:crlf\*(C'\fR | |
244 | layer corresponds to \*(L"text mode\*(R" on platforms that distinguish | |
245 | between the two modes when opening files (which is many DOS-like | |
246 | platforms, including Windows). These two layers are no-ops on | |
247 | platforms where \fIbinmode()\fR is a no\-op, but perform their functions | |
248 | everywhere if PerlIO is enabled. | |
249 | .SH "IMPLEMENTATION DETAILS" | |
250 | .IX Header "IMPLEMENTATION DETAILS" | |
251 | There is a class method in \f(CW\*(C`PerlIO::Layer\*(C'\fR \f(CW\*(C`find\*(C'\fR which is | |
252 | implemented as \s-1XS\s0 code. It is called by \f(CW\*(C`import\*(C'\fR to validate the | |
253 | layers: | |
254 | .PP | |
255 | .Vb 1 | |
256 | \& PerlIO::Layer::->find("perlio") | |
257 | .Ve | |
258 | .PP | |
259 | The return value (if defined) is a Perl object, of class | |
260 | \&\f(CW\*(C`PerlIO::Layer\*(C'\fR which is created by the C code in \fIperlio.c\fR. As | |
261 | yet there is nothing useful you can do with the object at the perl | |
262 | level. | |
263 | .SH "SEE ALSO" | |
264 | .IX Header "SEE ALSO" | |
265 | \&\*(L"binmode\*(R" in perlfunc, \*(L"open\*(R" in perlfunc, perlunicode, PerlIO, | |
266 | encoding |