base64.html
来自「perl教程」· HTML 代码 · 共 205 行
HTML
205 行
<?xml version="1.0" ?>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<html>
<head>
<!-- saved from url=(0017)http://localhost/ -->
<script language="JavaScript" src="../../displayToc.js"></script>
<script language="JavaScript" src="../../tocParas.js"></script>
<script language="JavaScript" src="../../tocTab.js"></script>
<link rel="stylesheet" type="text/css" href="../../scineplex.css">
<title>MIME::Base64 - Encoding and decoding of base64 strings</title>
<link rel="stylesheet" href="../../Active.css" type="text/css" />
<meta http-equiv="content-type" content="text/html; charset=utf-8" />
<link rev="made" href="mailto:" />
</head>
<body>
<script>writelinks('__top__',2);</script>
<h1><a>MIME::Base64 - Encoding and decoding of base64 strings</a></h1>
<p><a name="__index__"></a></p>
<!-- INDEX BEGIN -->
<ul>
<li><a href="#name">NAME</a></li>
<li><a href="#synopsis">SYNOPSIS</a></li>
<li><a href="#description">DESCRIPTION</a></li>
<li><a href="#diagnostics">DIAGNOSTICS</a></li>
<li><a href="#examples">EXAMPLES</a></li>
<li><a href="#copyright">COPYRIGHT</a></li>
<li><a href="#see_also">SEE ALSO</a></li>
</ul>
<!-- INDEX END -->
<hr />
<p>
</p>
<h1><a name="name">NAME</a></h1>
<p>MIME::Base64 - Encoding and decoding of base64 strings</p>
<p>
</p>
<hr />
<h1><a name="synopsis">SYNOPSIS</a></h1>
<pre>
<span class="keyword">use</span> <span class="variable">MIME::Base64</span><span class="operator">;</span>
</pre>
<pre>
<span class="variable">$encoded</span> <span class="operator">=</span> <span class="variable">encode_base64</span><span class="operator">(</span><span class="string">'Aladdin:open sesame'</span><span class="operator">);</span>
<span class="variable">$decoded</span> <span class="operator">=</span> <span class="variable">decode_base64</span><span class="operator">(</span><span class="variable">$encoded</span><span class="operator">);</span>
</pre>
<p>
</p>
<hr />
<h1><a name="description">DESCRIPTION</a></h1>
<p>This module provides functions to encode and decode strings into and from the
base64 encoding specified in RFC 2045 - <em>MIME (Multipurpose Internet
Mail Extensions)</em>. The base64 encoding is designed to represent
arbitrary sequences of octets in a form that need not be humanly
readable. A 65-character subset ([A-Za-z0-9+/=]) of US-ASCII is used,
enabling 6 bits to be represented per printable character.</p>
<p>The following functions are provided:</p>
<dl>
<dt><strong><a name="item_encode_base64"><code>encode_base64($str)</code></a></strong>
<dt><strong>encode_base64($str, $eol);</strong>
<dd>
<p>Encode data by calling the <a href="#item_encode_base64"><code>encode_base64()</code></a> function. The first
argument is the string to encode. The second argument is the
line-ending sequence to use. It is optional and defaults to "\n". The
returned encoded string is broken into lines of no more than 76
characters each and it will end with $eol unless it is empty. Pass an
empty string as second argument if you do not want the encoded string
to be broken into lines.</p>
</dd>
</li>
<dt><strong><a name="item_decode_base64"><code>decode_base64($str)</code></a></strong>
<dd>
<p>Decode a base64 string by calling the <a href="#item_decode_base64"><code>decode_base64()</code></a> function. This
function takes a single argument which is the string to decode and
returns the decoded data.</p>
</dd>
<dd>
<p>Any character not part of the 65-character base64 subset is
silently ignored. Characters occurring after a '=' padding character
are never decoded.</p>
</dd>
<dd>
<p>If the length of the string to decode, after ignoring
non-base64 chars, is not a multiple of 4 or if padding occurs too early,
then a warning is generated if perl is running under <a href="../../lib/Pod/perlrun.html#item__2dw"><code>-w</code></a>.</p>
</dd>
</li>
</dl>
<p>If you prefer not to import these routines into your namespace, you can
call them as:</p>
<pre>
<span class="keyword">use</span> <span class="variable">MIME::Base64</span> <span class="operator">();</span>
<span class="variable">$encoded</span> <span class="operator">=</span> <span class="variable">MIME::Base64::encode</span><span class="operator">(</span><span class="variable">$decoded</span><span class="operator">);</span>
<span class="variable">$decoded</span> <span class="operator">=</span> <span class="variable">MIME::Base64::decode</span><span class="operator">(</span><span class="variable">$encoded</span><span class="operator">);</span>
</pre>
<p>
</p>
<hr />
<h1><a name="diagnostics">DIAGNOSTICS</a></h1>
<p>The following warnings can be generated if perl is invoked with the
<a href="../../lib/Pod/perlrun.html#item__2dw"><code>-w</code></a> switch:</p>
<dl>
<dt><strong><a name="item_premature_end_of_base64_data">Premature end of base64 data</a></strong>
<dd>
<p>The number of characters to decode is not a multiple of 4. Legal
base64 data should be padded with one or two "=" characters to make
its length a multiple of 4. The decoded result will be the same
whether the padding is present or not.</p>
</dd>
</li>
<dt><strong><a name="item_premature_padding_of_base64_data">Premature padding of base64 data</a></strong>
<dd>
<p>The '=' padding character occurs as the first or second character
in a base64 quartet.</p>
</dd>
</li>
</dl>
<p>The following exception can be raised:</p>
<dl>
<dt><strong><a name="item_wide_character_in_subroutine_entry">Wide character in subroutine entry</a></strong>
<dd>
<p>The string passed to <a href="#item_encode_base64"><code>encode_base64()</code></a> contains characters with code
above 255. The base64 encoding is only defined for single-byte
characters. Use the Encode module to select the byte encoding you
want.</p>
</dd>
</li>
</dl>
<p>
</p>
<hr />
<h1><a name="examples">EXAMPLES</a></h1>
<p>If you want to encode a large file, you should encode it in chunks
that are a multiple of 57 bytes. This ensures that the base64 lines
line up and that you do not end up with padding in the middle. 57
bytes of data fills one complete base64 line (76 == 57*4/3):</p>
<pre>
<span class="keyword">use</span> <span class="variable">MIME::Base64</span> <span class="string">qw(encode_base64)</span><span class="operator">;</span>
</pre>
<pre>
<span class="keyword">open</span><span class="operator">(</span><span class="variable">FILE</span><span class="operator">,</span> <span class="string">"/var/log/wtmp"</span><span class="operator">)</span> <span class="keyword">or</span> <span class="keyword">die</span> <span class="string">"$!"</span><span class="operator">;</span>
<span class="keyword">while</span> <span class="operator">(</span><span class="keyword">read</span><span class="operator">(</span><span class="variable">FILE</span><span class="operator">,</span> <span class="variable">$buf</span><span class="operator">,</span> <span class="number">60</span><span class="operator">*</span><span class="number">57</span><span class="operator">))</span> <span class="operator">{</span>
<span class="keyword">print</span> <span class="variable">encode_base64</span><span class="operator">(</span><span class="variable">$buf</span><span class="operator">);</span>
<span class="operator">}</span>
</pre>
<p>or if you know you have enough memory</p>
<pre>
<span class="keyword">use</span> <span class="variable">MIME::Base64</span> <span class="string">qw(encode_base64)</span><span class="operator">;</span>
<span class="keyword">local</span><span class="operator">(</span><span class="variable">$/</span><span class="operator">)</span> <span class="operator">=</span> <span class="keyword">undef</span><span class="operator">;</span> <span class="comment"># slurp</span>
<span class="keyword">print</span> <span class="variable">encode_base64</span><span class="operator">(<</span><span class="variable">STDIN</span><span class="operator">>);</span>
</pre>
<p>The same approach as a command line:</p>
<pre>
perl -MMIME::Base64 -0777 -ne 'print encode_base64($_)' <file</pre>
<p>Decoding does not need slurp mode if every line contains a multiple
of four base64 chars:</p>
<pre>
perl -MMIME::Base64 -ne 'print decode_base64($_)' <file</pre>
<p>Perl v5.8 and better allow extended Unicode characters in strings.
Such strings cannot be encoded directly, as the base64
encoding is only defined for single-byte characters. The solution is
to use the Encode module to select the byte encoding you want. For
example:</p>
<pre>
<span class="keyword">use</span> <span class="variable">MIME::Base64</span> <span class="string">qw(encode_base64)</span><span class="operator">;</span>
<span class="keyword">use</span> <span class="variable">Encode</span> <span class="string">qw(encode)</span><span class="operator">;</span>
</pre>
<pre>
<span class="variable">$encoded</span> <span class="operator">=</span> <span class="variable">encode_base64</span><span class="operator">(</span><span class="variable">encode</span><span class="operator">(</span><span class="string">"UTF-8"</span><span class="operator">,</span> <span class="string">"\x{FFFF}\n"</span><span class="operator">));</span>
<span class="keyword">print</span> <span class="variable">$encoded</span><span class="operator">;</span>
</pre>
<p>
</p>
<hr />
<h1><a name="copyright">COPYRIGHT</a></h1>
<p>Copyright 1995-1999, 2001-2004 Gisle Aas.</p>
<p>This library is free software; you can redistribute it and/or
modify it under the same terms as Perl itself.</p>
<p>Distantly based on LWP::Base64 written by Martijn Koster
<<a href="mailto:m.koster@nexor.co.uk">m.koster@nexor.co.uk</a>> and Joerg Reichelt <<a href="mailto:j.reichelt@nexor.co.uk">j.reichelt@nexor.co.uk</a>> and
code posted to comp.lang.perl <<a href="mailto:3pd2lp$6gf@wsinti07.win.tue.nl">3pd2lp$6gf@wsinti07.win.tue.nl</a>> by Hans
Mulder <<a href="mailto:hansm@wsinti07.win.tue.nl">hansm@wsinti07.win.tue.nl</a>></p>
<p>The XS implementation uses code from metamail. Copyright 1991 Bell
Communications Research, Inc. (Bellcore)</p>
<p>
</p>
<hr />
<h1><a name="see_also">SEE ALSO</a></h1>
<p><a href="../../lib/MIME/QuotedPrint.html">the MIME::QuotedPrint manpage</a></p>
</body>
</html>
⌨️ 快捷键说明
复制代码Ctrl + C
搜索代码Ctrl + F
全屏模式F11
增大字号Ctrl + =
减小字号Ctrl + -
显示快捷键?