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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 |