1IO::HTML(3) User Contributed Perl Documentation IO::HTML(3)
2
6 IO::HTML - Open an HTML file with automatic charset detection
7
9 This document describes version 1.001 of IO::HTML, released June 28,
10 2014.
11
13 use IO::HTML; # exports html_file by default
14 use HTML::TreeBuilder;
15 my $tree = HTML::TreeBuilder->new_from_file(
17 html_file('foo.html')
18 );
19 # Alternative interface:
21 open(my $in, '<:raw', 'bar.html');
22 my $encoding = IO::HTML::sniff_encoding($in, 'bar.html');
23
25 IO::HTML provides an easy way to open a file containing HTML while
26 automatically determining its encoding. It uses the HTML5 encoding
27 sniffing algorithm specified in section 8.2.2.2 of the draft standard.
28 The algorithm as implemented here is:
30 1. If the file begins with a byte order mark indicating UTF-16LE,
32 UTF-16BE, or UTF-8, then that is the encoding.
33 2. If the first 1024 bytes of the file contain a "<meta>" tag that
35 indicates the charset, and Encode recognizes the specified charset
36 name, then that is the encoding. (This portion of the algorithm is
37 implemented by "find_charset_in".)
38 The "<meta>" tag can be in one of two formats:
40 <meta charset="...">
42 <meta http-equiv="Content-Type" content="...charset=...">
43 The search is case-insensitive, and the order of attributes within
45 the tag is irrelevant. Any additional attributes of the tag are
46 ignored. The first matching tag with a recognized encoding ends
47 the search.
48 3. If the first 1024 bytes of the file are valid UTF-8 (with at least
50 1 non-ASCII character), then the encoding is UTF-8.
51 4. If all else fails, use the default character encoding. The HTML5
53 standard suggests the default encoding should be locale dependent,
54 but currently it is always "cp1252" unless you set
55 $IO::HTML::default_encoding to a different value. Note:
56 "sniff_encoding" does not apply this step; only "html_file" does
57 that.
58
60 html_file
61 $filehandle = html_file($filename, \%options);
62 This function (exported by default) is the primary entry point. It
64 opens the file specified by $filename for reading, uses
65 "sniff_encoding" to find a suitable encoding layer, and applies it. It
66 also applies the ":crlf" layer. If the file begins with a BOM, the
67 filehandle is positioned just after the BOM.
68 The optional second argument is a hashref containing options. The
70 possible keys are described under "find_charset_in".
71 If "sniff_encoding" is unable to determine the encoding, it defaults to
73 $IO::HTML::default_encoding, which is set to "cp1252" (a.k.a.
74 Windows-1252) by default. According to the standard, the default
75 should be locale dependent, but that is not currently implemented.
76 It dies if the file cannot be opened.
78 html_file_and_encoding
80 ($filehandle, $encoding, $bom)
81 = html_file_and_encoding($filename, \%options);
82 This function (exported only by request) is just like "html_file", but
84 returns more information. In addition to the filehandle, it returns
85 the name of the encoding used, and a flag indicating whether a byte
86 order mark was found (if $bom is true, the file began with a BOM).
87 This may be useful if you want to write the file out again (especially
88 in conjunction with the "html_outfile" function).
89 The optional second argument is a hashref containing options. The
91 possible keys are described under "find_charset_in".
92 It dies if the file cannot be opened. The result of calling it in
94 scalar context is undefined.
95 html_outfile
97 $filehandle = html_outfile($filename, $encoding, $bom);
98 This function (exported only by request) opens $filename for output
100 using $encoding, and writes a BOM to it if $bom is true. If $encoding
101 is "undef", it defaults to $IO::HTML::default_encoding. $encoding may
102 be either an encoding name or an Encode::Encoding object.
103 It dies if the file cannot be opened.
105 sniff_encoding
107 ($encoding, $bom) = sniff_encoding($filehandle, $filename, \%options);
108 This function (exported only by request) runs the HTML5 encoding
110 sniffing algorithm on $filehandle (which must be seekable, and should
111 have been opened in ":raw" mode). $filename is used only for error
112 messages (if there's a problem using the filehandle), and defaults to
113 "file" if omitted. The optional third argument is a hashref containing
114 options. The possible keys are described under "find_charset_in".
115 It returns Perl's canonical name for the encoding, which is not
117 necessarily the same as the MIME or IANA charset name. It returns
118 "undef" if the encoding cannot be determined. $bom is true if the file
119 began with a byte order mark. In scalar context, it returns only
120 $encoding.
121 The filehandle's position is restored to its original position
123 (normally the beginning of the file) unless $bom is true. In that
124 case, the position is immediately after the BOM.
125 Tip: If you want to run "sniff_encoding" on a file you've already
127 loaded into a string, open an in-memory file on the string, and pass
128 that handle:
129 ($encoding, $bom) = do {
131 open(my $fh, '<', \$string); sniff_encoding($fh)
132 };
133 (This only makes sense if $string contains bytes, not characters.)
135 find_charset_in
137 $encoding = find_charset_in($string_containing_HTML, \%options);
138 This function (exported only by request) looks for charset information
140 in a "<meta>" tag in a possibly incomplete HTML document using the "two
141 step" algorithm specified by HTML5. It does not look for a BOM. Only
142 the first 1024 bytes of the string are checked.
143 It returns Perl's canonical name for the encoding, which is not
145 necessarily the same as the MIME or IANA charset name. It returns
146 "undef" if no charset is specified or if the specified charset is not
147 recognized by the Encode module.
148 The optional second argument is a hashref containing options. The
150 following keys are recognized:
151 "encoding"
153 If true, return the Encode::Encoding object instead of its name.
154 Defaults to false.
155 "need_pragma"
157 If true (the default), follow the HTML5 spec and examine the
158 "content" attribute only of "<meta http-equiv="Content-Type"". If
159 set to 0, relax the HTML5 spec, and look for "charset=" in the
160 "content" attribute of every meta tag.
161
163 By default, only "html_file" is exported. Other functions may be
164 exported on request.
165 For people who prefer not to export functions, all functions beginning
167 with "html_" have an alias without that prefix (e.g. you can call
168 "IO::HTML::file(...)" instead of "IO::HTML::html_file(...)". These
169 aliases are not exportable.
170 The following export tags are available:
172 ":all"
174 All exportable functions.
175 ":rw"
177 "html_file", "html_file_and_encoding", "html_outfile".
178
180 The HTML5 specification, section 8.2.2.2 Determining the character
181 encoding:
182 <http://www.w3.org/TR/html5/syntax.html#determining-the-character-encoding>
183
185 "Could not read %s: %s"
186 The specified file could not be read from for the reason specified
187 by $!.
188 "Could not seek %s: %s"
190 The specified file could not be rewound for the reason specified by
191 $!.
192 "Failed to open %s: %s"
194 The specified file could not be opened for reading for the reason
195 specified by $!.
196 "No default encoding specified"
198 The "sniff_encoding" algorithm didn't find an encoding to use, and
199 you set $IO::HTML::default_encoding to "undef".
200
202 IO::HTML requires no configuration files or environment variables.
203
205 IO::HTML has no non-core dependencies for Perl 5.8.7+. With earlier
206 versions of Perl 5.8, you need to upgrade Encode to at least version
207 2.10, and you may need to upgrade Exporter to at least version 5.57.
208
210 None reported.
211
213 No bugs have been reported.
214
216 Christopher J. Madsen "<perl AT cjmweb.net>"
217 Please report any bugs or feature requests to
219 "<bug-IO-HTML AT rt.cpan.org>" or through the web interface at
220 <http://rt.cpan.org/Public/Bug/Report.html?Queue=IO-HTML>.
221 You can follow or contribute to IO-HTML's development at
223 <https://github.com/madsen/io-html>.
224
226 This software is copyright (c) 2014 by Christopher J. Madsen.
227 This is free software; you can redistribute it and/or modify it under
229 the same terms as the Perl 5 programming language system itself.
230
232 BECAUSE THIS SOFTWARE IS LICENSED FREE OF CHARGE, THERE IS NO WARRANTY
233 FOR THE SOFTWARE, TO THE EXTENT PERMITTED BY APPLICABLE LAW. EXCEPT
234 WHEN OTHERWISE STATED IN WRITING THE COPYRIGHT HOLDERS AND/OR OTHER
235 PARTIES PROVIDE THE SOFTWARE "AS IS" WITHOUT WARRANTY OF ANY KIND,
236 EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
237 WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE
238 ENTIRE RISK AS TO THE QUALITY AND PERFORMANCE OF THE SOFTWARE IS WITH
239 YOU. SHOULD THE SOFTWARE PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL
240 NECESSARY SERVICING, REPAIR, OR CORRECTION.
241 IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING
243 WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MAY MODIFY AND/OR
244 REDISTRIBUTE THE SOFTWARE AS PERMITTED BY THE ABOVE LICENSE, BE LIABLE
245 TO YOU FOR DAMAGES, INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL, OR
246 CONSEQUENTIAL DAMAGES ARISING OUT OF THE USE OR INABILITY TO USE THE
247 SOFTWARE (INCLUDING BUT NOT LIMITED TO LOSS OF DATA OR DATA BEING
248 RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD PARTIES OR A
249 FAILURE OF THE SOFTWARE TO OPERATE WITH ANY OTHER SOFTWARE), EVEN IF
250 SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH
251 DAMAGES.
252perl v5.32.0 2020-07-28 IO::HTML(3)