147 lines
5.0 KiB
Groff
147 lines
5.0 KiB
Groff
.\" $NetBSD: uuencode.5,v 1.11 2008/08/25 09:36:24 wiz Exp $
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.\"
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.\" Copyright (c) 1989, 1991, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)uuencode.format.5 8.2 (Berkeley) 1/12/94
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.\"
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.Dd April 9, 1997
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.Dt UUENCODE 5
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.Os
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.Sh NAME
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.Nm uuencode
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.Nd format of an encoded uuencode file
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.Sh DESCRIPTION
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Files output by
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.Xr uuencode 1
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consist of a header line,
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followed by a number of body lines,
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and a trailer line.
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The
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.Xr uudecode 1
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command
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will ignore any lines preceding the header or
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following the trailer.
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Lines preceding a header must not, of course,
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look like a header.
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.Pp
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The header line starts with the word
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.Dq begin ,
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a space,
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a file mode (in octal),
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a space,
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and finally a string which names the file being encoded.
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.Pp
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The central engine of
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.Xr uuencode 1
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is a six-bit encoding function which outputs an
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.Tn ASCII
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character.
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The six bits to be encoded are treated as a small integer and added
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with the
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.Tn ASCII
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value for the space character (octal 40).
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The result is a printable
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.Tn ASCII
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character.
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In the case where all six bits to be encoded are zero,
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the
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.Tn ASCII
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backquote character \` (octal 140) is emitted instead of what
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would normally be a space.
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.Pp
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The body of an encoded file consists of one or more lines,
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each of which may be a maximum of 86 characters long (including the trailing
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newline).
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Each line represents an encoded chunk of data from the input file and begins
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with a byte count,
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followed by encoded bytes,
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followed by a newline.
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.Pp
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The byte count is a six-bit integer encoded with the above function,
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representing the number of bytes encoded in the rest of the line.
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The method used to encode the data expands its size by
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133% (described below).
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Therefore it is important to note that the byte count describes the size of
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the chunk of data before it is encoded, not afterwards.
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The six bit size of this number effectively limits the number of bytes
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that can be encoded in each line to a maximum of 63.
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While
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.Xr uuencode 1
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will not encode more than 45 bytes per line,
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.Xr uudecode 1
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will tolerate the maximum line size.
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.Pp
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The remaining characters in the line represent the data of the input
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file encoded as follows.
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Input data are broken into groups of three eight-bit bytes,
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which are then interpreted together as a 24-bit block.
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The first bit of the block is the highest order bit of the first character,
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and the last is the lowest order bit of the third character.
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This block is then broken into four six-bit integers which are encoded one by
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one starting from the first bit of the block.
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The result is a four character
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.Tn ASCII
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string for every three bytes of input data.
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.Pp
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Encoded lines of data continue in this manner until the input file is
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exhausted.
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The end of the body is signaled by an encoded line with a byte count
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of zero (the
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.Tn ASCII
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backquote character \`).
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.Pp
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Obviously, not every input file will be a multiple of three bytes in size.
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In these cases,
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.Xr uuencode 1
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will pad the remaining one or two bytes of data with garbage bytes until
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a three byte group is created.
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The byte count in a line containing
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garbage padding will reflect the actual number of bytes encoded, making
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it possible to convey how many bytes are garbage.
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.Pp
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The trailer line consists of
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.Dq end
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on a line by itself.
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.Sh SEE ALSO
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.Xr mail 1 ,
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.Xr uucp 1 ,
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.Xr uudecode 1 ,
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.Xr uuencode 1 ,
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.Xr ascii 7
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.Sh HISTORY
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The
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.Nm
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file format appeared in
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.Bx 4.0 .
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.Sh BUGS
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The interpretation of the
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.Nm
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format relies on properties of the
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.Tn ASCII
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character set and may not work correctly on non-ASCII systems.
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