mingw/html/lib/MIME/Base64.html

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  13 <big><strong><span class="block">&nbsp;MIME::Base64 - Encoding and decoding of base64 strings</span></strong></big>
  14 </td></tr>
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  16
  17 <p><a name="__index__"></a></p>
  18 <!-- INDEX BEGIN -->
  19
  20 <ul>
  21
  22         <li><a href="#name">NAME</a></li>
  23         <li><a href="#synopsis">SYNOPSIS</a></li>
  24         <li><a href="#description">DESCRIPTION</a></li>
  25         <li><a href="#diagnostics">DIAGNOSTICS</a></li>
  26         <li><a href="#examples">EXAMPLES</a></li>
  27         <li><a href="#copyright">COPYRIGHT</a></li>
  28         <li><a href="#see_also">SEE ALSO</a></li>
  29 </ul>
  30 <!-- INDEX END -->
  31
  32 <hr />
  33 <p>
  34 </p>
  35 <h1><a name="name">NAME</a></h1>
  36 <p>MIME::Base64 - Encoding and decoding of base64 strings</p>
  37 <p>
  38 </p>
  39 <hr />
  40 <h1><a name="synopsis">SYNOPSIS</a></h1>
  41 <pre>
  42  use MIME::Base64;</pre>
  43 <pre>
  44  $encoded = encode_base64('Aladdin:open sesame');
  45  $decoded = decode_base64($encoded);</pre>
  46 <p>
  47 </p>
  48 <hr />
  49 <h1><a name="description">DESCRIPTION</a></h1>
  50 <p>This module provides functions to encode and decode strings into and from the
  51 base64 encoding specified in RFC 2045 - <em>MIME (Multipurpose Internet
  52 Mail Extensions)</em>. The base64 encoding is designed to represent
  53 arbitrary sequences of octets in a form that need not be humanly
  54 readable. A 65-character subset ([A-Za-z0-9+/=]) of US-ASCII is used,
  55 enabling 6 bits to be represented per printable character.</p>
  56 <p>The following functions are provided:</p>
  57 <dl>
  58 <dt><strong><a name="item_encode_base64"><code>encode_base64($str)</code></a></strong>
  59
  60 <dt><strong>encode_base64($str, $eol);</strong>
  61
  62 <dd>
  63 <p>Encode data by calling the <a href="#item_encode_base64"><code>encode_base64()</code></a> function.  The first
  64 argument is the string to encode.  The second argument is the
  65 line-ending sequence to use.  It is optional and defaults to ``\n''.  The
  66 returned encoded string is broken into lines of no more than 76
  67 characters each and it will end with $eol unless it is empty.  Pass an
  68 empty string as second argument if you do not want the encoded string
  69 to be broken into lines.</p>
  70 </dd>
  71 </li>
  72 <dt><strong><a name="item_decode_base64"><code>decode_base64($str)</code></a></strong>
  73
  74 <dd>
  75 <p>Decode a base64 string by calling the <a href="#item_decode_base64"><code>decode_base64()</code></a> function.  This
  76 function takes a single argument which is the string to decode and
  77 returns the decoded data.</p>
  78 </dd>
  79 <dd>
  80 <p>Any character not part of the 65-character base64 subset is
  81 silently ignored.  Characters occurring after a '=' padding character
  82 are never decoded.</p>
  83 </dd>
  84 <dd>
  85 <p>If the length of the string to decode, after ignoring
  86 non-base64 chars, is not a multiple of 4 or if padding occurs too early,
  87 then a warning is generated if perl is running under <code>-w</code>.</p>
  88 </dd>
  89 </li>
  90 </dl>
  91 <p>If you prefer not to import these routines into your namespace, you can
  92 call them as:</p>
  93 <pre>
  94     use MIME::Base64 ();
  95     $encoded = MIME::Base64::encode($decoded);
  96     $decoded = MIME::Base64::decode($encoded);</pre>
  97 <p>
  98 </p>
  99 <hr />
 100 <h1><a name="diagnostics">DIAGNOSTICS</a></h1>
 101 <p>The following warnings can be generated if perl is invoked with the
 102 <code>-w</code> switch:</p>
 103 <dl>
 104 <dt><strong><a name="item_premature_end_of_base64_data">Premature end of base64 data</a></strong>
 105
 106 <dd>
 107 <p>The number of characters to decode is not a multiple of 4.  Legal
 108 base64 data should be padded with one or two ``='' characters to make
 109 its length a multiple of 4.  The decoded result will be the same
 110 whether the padding is present or not.</p>
 111 </dd>
 112 </li>
 113 <dt><strong><a name="item_premature_padding_of_base64_data">Premature padding of base64 data</a></strong>
 114
 115 <dd>
 116 <p>The '=' padding character occurs as the first or second character
 117 in a base64 quartet.</p>
 118 </dd>
 119 </li>
 120 </dl>
 121 <p>The following exception can be raised:</p>
 122 <dl>
 123 <dt><strong><a name="item_wide_character_in_subroutine_entry">Wide character in subroutine entry</a></strong>
 124
 125 <dd>
 126 <p>The string passed to <a href="#item_encode_base64"><code>encode_base64()</code></a> contains characters with code
 127 above 255.  The base64 encoding is only defined for single-byte
 128 characters.  Use the Encode module to select the byte encoding you
 129 want.</p>
 130 </dd>
 131 </li>
 132 </dl>
 133 <p>
 134 </p>
 135 <hr />
 136 <h1><a name="examples">EXAMPLES</a></h1>
 137 <p>If you want to encode a large file, you should encode it in chunks
 138 that are a multiple of 57 bytes.  This ensures that the base64 lines
 139 line up and that you do not end up with padding in the middle. 57
 140 bytes of data fills one complete base64 line (76 == 57*4/3):</p>
 141 <pre>
 142    use MIME::Base64 qw(encode_base64);</pre>
 143 <pre>
 144    open(FILE, &quot;/var/log/wtmp&quot;) or die &quot;$!&quot;;
 145    while (read(FILE, $buf, 60*57)) {
 146        print encode_base64($buf);
 147    }</pre>
 148 <p>or if you know you have enough memory</p>
 149 <pre>
 150    use MIME::Base64 qw(encode_base64);
 151    local($/) = undef;  # slurp
 152    print encode_base64(&lt;STDIN&gt;);</pre>
 153 <p>The same approach as a command line:</p>
 154 <pre>
 155    perl -MMIME::Base64 -0777 -ne 'print encode_base64($_)' &lt;file</pre>
 156 <p>Decoding does not need slurp mode if every line contains a multiple
 157 of four base64 chars:</p>
 158 <pre>
 159    perl -MMIME::Base64 -ne 'print decode_base64($_)' &lt;file</pre>
 160 <p>Perl v5.8 and better allow extended Unicode characters in strings.
 161 Such strings cannot be encoded directly, as the base64
 162 encoding is only defined for single-byte characters.  The solution is
 163 to use the Encode module to select the byte encoding you want.  For
 164 example:</p>
 165 <pre>
 166     use MIME::Base64 qw(encode_base64);
 167     use Encode qw(encode);</pre>
 168 <pre>
 169     $encoded = encode_base64(encode(&quot;UTF-8&quot;, &quot;\x{FFFF}\n&quot;));
 170     print $encoded;</pre>
 171 <p>
 172 </p>
 173 <hr />
 174 <h1><a name="copyright">COPYRIGHT</a></h1>
 175 <p>Copyright 1995-1999, 2001-2004 Gisle Aas.</p>
 176 <p>This library is free software; you can redistribute it and/or
 177 modify it under the same terms as Perl itself.</p>
 178 <p>Distantly based on LWP::Base64 written by Martijn Koster
 179 &lt;<a href="mailto:m.koster@nexor.co.uk">m.koster@nexor.co.uk</a>&gt; and Joerg Reichelt &lt;<a href="mailto:j.reichelt@nexor.co.uk">j.reichelt@nexor.co.uk</a>&gt; and
 180 code posted to comp.lang.perl &lt;<a href="mailto:3pd2lp$6gf@wsinti07.win.tue.nl">3pd2lp$6gf@wsinti07.win.tue.nl</a>&gt; by Hans
 181 Mulder &lt;<a href="mailto:hansm@wsinti07.win.tue.nl">hansm@wsinti07.win.tue.nl</a>&gt;</p>
 182 <p>The XS implementation uses code from metamail.  Copyright 1991 Bell
 183 Communications Research, Inc. (Bellcore)</p>
 184 <p>
 185 </p>
 186 <hr />
 187 <h1><a name="see_also">SEE ALSO</a></h1>
 188 <p><a href="file://C|\msysgit\mingw\html/lib/MIME/QuotedPrint.html">the MIME::QuotedPrint manpage</a></p>
 189 <table border="0" width="100%" cellspacing="0" cellpadding="3">
 190 <tr><td class="block" style="background-color: #cccccc" valign="middle">
 191 <big><strong><span class="block">&nbsp;MIME::Base64 - Encoding and decoding of base64 strings</span></strong></big>
 192 </td></tr>
 193 </table>
 194
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