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Quoted-Printable

The Quoted-Printable encoding is, like Base64, part of the MIME standard, described in [RFC1521]. It is not suitable for encoding arbitrary binary data, but is intended for ``data that largely consists of octets that correspond to printable characters''. It is widely in use in countries with an extended character set, where characters like the German umlauts `ä' or `ß' are represented by non-ASCII characters with the highest bit set.

The essence of the encoding is that arbitrary octets can be represented by an equal sign `=' followed by two hexadecimal digits. The equal sign itself, for example, is encoded as ``=3D''.

Quoted-Printable enforces a maximum line length of 76 characters. Longer lines can be wrapped using soft line breaks. If the last character of an encoded line is an equal sign, the following line break is to be ignored.

It would indeed be possible to transfer arbitrary binary data using this encoding, but care must be taken with line breaks, which are converted from native format on the sender's side and back into native format on the recipient's side. However, the native representations may differ. But this alternative is hardly worth considering, since for arbitrary data, quoted-printable is substantially less effective than Base64.

Please refer to the original document, [RFC1521], for a complete discussion of the encoding.

Here is how the example file could look like in Quoted-Printable encoding.

This is a test file for =
illustrating the various
encoding methods=2e=20=
Let=27s make this text=
 longer than
=357 bytes to wrap lines =
with Base64 data=2c too=2e
Greetings=2c Frank Pilhofer


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Next: About this document ... Up: Encoding Formats Previous: BinHex encoding
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