open - perl pragma to set default PerlIO layers for input and output

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Any two-argument open(), readpipe() (aka qx//) and similar operators found within the lexical scope of this pragma will use the declared defaults. Three-argument opens are not affected by this pragma since there you (can) explicitly specify the layers and are supposed to know what you are doing.</p> <p>With the <code>IN</code> subpragma you can declare the default layers of input streams, and with the <code>OUT</code> subpragma you can declare the default layers of output streams. With the <code>IO</code> subpragma you can control both input and output streams simultaneously.</p> <p>If you have a legacy encoding, you can use the <code>:encoding(...)</code> tag.</p> <p>if you want to set your encoding layers based on your locale environment variables, you can use the <code>:locale</code> tag. For example:</p> <pre><code>$ENV{LANG} = 'ru_RU.KOI8-R'; # the :locale will probe the locale environment variables like LANG use open OUT => ':locale'; open(O, ">koi8"); print O chr(0x430); # Unicode CYRILLIC SMALL LETTER A = KOI8-R 0xc1 close O; open(I, "<koi8"); printf "%#x\n", ord(<I>), "\n"; # this should print 0xc1 close I;</code></pre> <p>These are equivalent</p> <pre><code>use open ':utf8'; use open IO => ':utf8';</code></pre> <p>as are these</p> <pre><code>use open ':locale'; use open IO => ':locale';</code></pre> <p>and these</p> <pre><code>use open ':encoding(iso-8859-7)'; use open IO => ':encoding(iso-8859-7)';</code></pre> <p>The matching of encoding names is loose: case does not matter, and many encodings have several aliases. See <a href="/5.8.5/Encode::Supported">Encode::Supported</a> for details and the list of supported locales.</p> <p>Note that <code>:utf8</code> PerlIO layer must always be specified exactly like that, it is not subject to the loose matching of encoding names.</p> <p>When open() is given an explicit list of layers they are appended to the list declared using this pragma.</p> <p>The <code>:std</code> subpragma on its own has no effect, but if combined with the <code>:utf8</code> or <code>:encoding</code> subpragmas, it converts the standard filehandles (STDIN, STDOUT, STDERR) to comply with encoding selected for input/output handles. For example, if both input and out are chosen to be <code>:utf8</code>, a <code>:std</code> will mean that STDIN, STDOUT, and STDERR are also in <code>:utf8</code>. On the other hand, if only output is chosen to be in <code>:encoding(koi8r)</code>, a <code>:std</code> will cause only the STDOUT and STDERR to be in <code>koi8r</code>. The <code>:locale</code> subpragma implicitly turns on <code>:std</code>.</p> <p>The logic of <code>:locale</code> is as follows:</p> <ol> <li><p>If the platform supports the langinfo(CODESET) interface, the codeset returned is used as the default encoding for the open pragma.</p> </li> <li><p>If 1. didn't work but we are under the locale pragma, the environment variables LC_ALL and LANG (in that order) are matched for encodings (the part after <code>.</code>, if any), and if any found, that is used as the default encoding for the open pragma.</p> </li> <li><p>If 1. and 2. didn't work, the environment variables LC_ALL and LANG (in that order) are matched for anything looking like UTF-8, and if any found, <code>:utf8</code> is used as the default encoding for the open pragma.</p> </li> </ol> <p>If your locale environment variables (LC_ALL, LC_CTYPE, LANG) contain the strings 'UTF-8' or 'UTF8' (case-insensitive matching), the default encoding of your STDIN, STDOUT, and STDERR, and of <b>any subsequent file open</b>, is UTF-8.</p> <p>Directory handles may also support PerlIO layers in the future.</p> <h1 id="NONPERLIO-FUNCTIONALITY"><a class="permalink" href="#NONPERLIO-FUNCTIONALITY">#</a><a id="NONPERLIO"></a>NONPERLIO FUNCTIONALITY</h1> <p>If Perl is not built to use PerlIO as its IO system then only the two pseudo-layers <code>:bytes</code> and <code>:crlf</code> are available.</p> <p>The <code>:bytes</code> layer corresponds to "binary mode" and the <code>:crlf</code> layer corresponds to "text mode" on platforms that distinguish between the two modes when opening files (which is many DOS-like platforms, including Windows). These two layers are no-ops on platforms where binmode() is a no-op, but perform their functions everywhere if PerlIO is enabled.</p> <h1 id="IMPLEMENTATION-DETAILS"><a class="permalink" href="#IMPLEMENTATION-DETAILS">#</a><a id="IMPLEMENTATION"></a>IMPLEMENTATION DETAILS</h1> <p>There is a class method in <code>PerlIO::Layer</code> <code>find</code> which is implemented as XS code. It is called by <code>import</code> to validate the layers:</p> <pre><code>PerlIO::Layer::->find("perlio")</code></pre> <p>The return value (if defined) is a Perl object, of class <code>PerlIO::Layer</code> which is created by the C code in <i>perlio.c</i>. As yet there is nothing useful you can do with the object at the perl level.</p> <h1 id="SEE-ALSO"><a class="permalink" href="#SEE-ALSO">#</a><a id="SEE"></a>SEE ALSO</h1> <p><a href="/5.8.5/perlfunc#binmode">"binmode" in perlfunc</a>, <a href="/5.8.5/perlfunc#open">"open" in perlfunc</a>, <a href="/5.8.5/perlunicode">perlunicode</a>, <a href="/5.8.5/PerlIO">PerlIO</a>, <a href="/5.8.5/encoding">encoding</a></p> </div> <div id="footer"> <p>Perldoc Browser is maintained by Dan Book (<a href="https://metacpan.org/author/DBOOK">DBOOK</a>). Please contact him via the <a href="https://github.com/Grinnz/perldoc-browser/issues">GitHub issue tracker</a> or <a href="mailto:dbook@cpan.org">email</a> regarding any issues with the site itself, search, or rendering of documentation.</p> <p>The Perl documentation is maintained by the Perl 5 Porters in the development of Perl. Please contact them via the <a href="https://github.com/Perl/perl5/issues">Perl issue tracker</a>, the <a href="https://lists.perl.org/list/perl5-porters.html">mailing list</a>, or <a href="https://kiwiirc.com/client/irc.perl.org/p5p">IRC</a> to report any issues with the contents or format of the documentation.</p> </div> </div> <script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.5.1/jquery.slim.min.js" integrity="sha512-/DXTXr6nQodMUiq+IUJYCt2PPOUjrHJ9wFrqpJ3XkgPNOZVfMok7cRw6CSxyCQxXn6ozlESsSh1/sMCTF1rL/g==" crossorigin="anonymous"></script> <script src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.16.1/umd/popper.min.js" integrity="sha512-ubuT8Z88WxezgSqf3RLuNi5lmjstiJcyezx34yIU2gAHonIi27Na7atqzUZCOoY4CExaoFumzOsFQ2Ch+I/HCw==" crossorigin="anonymous"></script> <script src="https://stackpath.bootstrapcdn.com/bootstrap/4.5.2/js/bootstrap.min.js" integrity="sha384-B4gt1jrGC7Jh4AgTPSdUtOBvfO8shuf57BaghqFfPlYxofvL8/KUEfYiJOMMV+rV" crossorigin="anonymous"></script> <script src="/js/highlight.pack.js"></script> <script>hljs.highlightAll();</script> </body> </html>

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open - perl pragma to set default PerlIO layers for input and output - Perldoc Browser