UUENCODE(1P) POSIX Programmer's Manual UUENCODE(1P)
PROLOG
This manual page is part of the POSIX Programmer's Manual. The Linux
implementation of this interface may differ (consult the corresponding
Linux manual page for details of Linux behavior), or the interface may
not be implemented on Linux.
NAME
uuencode - encode a binary file
SYNOPSIS
uuencode [-m][file] decode_pathname
DESCRIPTION
The uuencode utility shall write an encoded version of the named input
file, or standard input if no file is specified, to standard output.
The output shall be encoded using one of the algorithms described in
the STDOUT section and shall include the file access permission bits
(in chmod octal or symbolic notation) of the input file and the
decode_pathname, for re-creation of the file on another system that
conforms to this volume of IEEE Std 1003.1-2001.
OPTIONS
The uuencode utility shall conform to the Base Definitions volume of
IEEE Std 1003.1-2001, Section 12.2, Utility Syntax Guidelines.
The following option shall be supported by the implementation:
-m Encode the output using the MIME Base64 algorithm described in
STDOUT. If -m is not specified, the historical algorithm
described in STDOUT shall be used.
OPERANDS
The following operands shall be supported:
decode_pathname
The pathname of the file into which the uudecode utility shall
place the decoded file. Specifying a decode_pathname operand of
/dev/stdout shall indicate that uudecode is to use standard out-
put. If there are characters in decode_pathname that are not in
the portable filename character set the results are unspecified.
file A pathname of the file to be encoded.
STDIN
See the INPUT FILES section.
INPUT FILES
Input files can be files of any type.
ENVIRONMENT VARIABLES
The following environment variables shall affect the execution of uuen-
code:
LANG Provide a default value for the internationalization variables
that are unset or null. (See the Base Definitions volume of
IEEE Std 1003.1-2001, Section 8.2, Internationalization Vari-
ables for the precedence of internationalization variables used
to determine the values of locale categories.)
LC_ALL If set to a non-empty string value, override the values of all
the other internationalization variables.
LC_CTYPE
Determine the locale for the interpretation of sequences of
bytes of text data as characters (for example, single-byte as
opposed to multi-byte characters in arguments and input files).
LC_MESSAGES
Determine the locale that should be used to affect the format
and contents of diagnostic messages written to standard error.
NLSPATH
Determine the location of message catalogs for the processing of
LC_MESSAGES .
ASYNCHRONOUS EVENTS
Default.
STDOUT
uuencode Base64 Algorithm
The standard output shall be a text file (encoded in the character set
of the current locale) that begins with the line:
"begin-base64 %s %s\n", <mode>, <decode_pathname>
and ends with the line:
"====\n"
In both cases, the lines shall have no preceding or trailing <blank>s.
The encoding process represents 24-bit groups of input bits as output
strings of four encoded characters. Proceeding from left to right, a
24-bit input group shall be formed by concatenating three 8-bit input
groups. Each 24-bit input group then shall be treated as four concate-
nated 6-bit groups, each of which shall be translated into a single
digit in the Base64 alphabet. When encoding a bit stream via the Base64
encoding, the bit stream shall be presumed to be ordered with the most-
significant bit first. That is, the first bit in the stream shall be
the high-order bit in the first byte, and the eighth bit shall be the
low-order bit in the first byte, and so on. Each 6-bit group is used as
an index into an array of 64 printable characters, as shown in uuencode
Base64 Values .
Table: uuencode Base64 Values
Value Encoding Value Encoding Value Encoding Value Encoding
0 A 17 R 34 i 51 z
1 B 18 S 35 j 52 0
2 C 19 T 36 k 53 1
3 D 20 U 37 l 54 2
4 E 21 V 38 m 55 3
5 F 22 W 39 n 56 4
6 G 23 X 40 o 57 5
7 H 24 Y 41 p 58 6
8 I 25 Z 42 q 59 7
9 J 26 a 43 r 60 8
10 K 27 b 44 s 61 9
11 L 28 c 45 t 62 +
12 M 29 d 46 u 63 /
13 N 30 e 47 v
14 O 31 f 48 w (pad)----------
15 P 32 g 49 x
16 Q 33 h 50 y
The character referenced by the index shall be placed in the output
string.
The output stream (encoded bytes) shall be represented in lines of no
more than 76 characters each. All line breaks or other characters not
found in the table shall be ignored by decoding software (see uudecode
).
Special processing shall be performed if fewer than 24 bits are avail-
able at the end of a message or encapsulated part of a message. A full
encoding quantum shall always be completed at the end of a message.
When fewer than 24 input bits are available in an input group, zero
bits shall be added (on the right) to form an integral number of 6-bit
groups. Output character positions that are not required to represent
actual input data shall be set to the character '=' . Since all Base64
input is an integral number of octets, only the following cases can
arise:
1. The final quantum of encoding input is an integral multiple of 24
bits; here, the final unit of encoded output shall be an integral
multiple of 4 characters with no '=' padding.
2. The final quantum of encoding input is exactly 16 bits; here, the
final unit of encoded output shall be three characters followed by
one '=' padding character.
3. The final quantum of encoding input is exactly 8 bits; here, the
final unit of encoded output shall be two characters followed by
two '=' padding characters.
A terminating "====" evaluates to nothing and denotes the end of the
encoded data.
uuencode Historical Algorithm
The standard output shall be a text file (encoded in the character set
of the current locale) that begins with the line:
"begin %s %s\n" <mode>, <decode_pathname>
and ends with the line:
"end\n"
In both cases, the lines shall have no preceding or trailing <blank>s.
The algorithm that shall be used for lines in between begin and end
takes three octets as input and writes four characters of output by
splitting the input at six-bit intervals into four octets, containing
data in the lower six bits only. These octets shall be converted to
characters by adding a value of 0x20 to each octet, so that each octet
is in the range [0x20,0x5f], and then it shall be assumed to represent
a printable character in the ISO/IEC 646:1991 standard encoded charac-
ter set. It then shall be translated into the corresponding character
codes for the codeset in use in the current locale. (For example, the
octet 0x41, representing 'A', would be translated to 'A' in the current
codeset, such as 0xc1 if it were EBCDIC.)
Where the bits of two octets are combined, the least significant bits
of the first octet shall be shifted left and combined with the most
significant bits of the second octet shifted right. Thus the three
octets A, B, C shall be converted into the four octets:
0x20 + (( A >> 2 ) & 0x3F)
0x20 + (((A << 4) | ((B >> 4) & 0xF)) & 0x3F)
0x20 + (((B << 2) | ((C >> 6) & 0x3)) & 0x3F)
0x20 + (( C ) & 0x3F)
These octets then shall be translated into the local character set.
Each encoded line contains a length character, equal to the number of
characters to be decoded plus 0x20 translated to the local character
set as described above, followed by the encoded characters. The maxi-
mum number of octets to be encoded on each line shall be 45.
STDERR
The standard error shall be used only for diagnostic messages.
OUTPUT FILES
None.
EXTENDED DESCRIPTION
None.
EXIT STATUS
The following exit values shall be returned:
0 Successful completion.
>0 An error occurred.
CONSEQUENCES OF ERRORS
Default.
The following sections are informative.
APPLICATION USAGE
The file is expanded by 35 percent (each three octets become four, plus
control information) causing it to take longer to transmit.
Since this utility is intended to create files to be used for data
interchange between systems with possibly different codesets, and to
represent binary data as a text file, the ISO/IEC 646:1991 standard was
chosen for a midpoint in the algorithm as a known reference point. The
output from uuencode is a text file on the local system. If the output
were in the ISO/IEC 646:1991 standard codeset, it might not be a text
file (at least because the <newline>s might not match), and the goal of
creating a text file would be defeated. If this text file was then car-
ried to another machine with the same codeset, it would be perfectly
compatible with that system's uudecode. If it was transmitted over a
mail system or sent to a machine with a different codeset, it is
assumed that, as for every other text file, some translation mechanism
would convert it (by the time it reached a user on the other system)
into an appropriate codeset. This translation only makes sense from the
local codeset, not if the file has been put into a ISO/IEC 646:1991
standard representation first. Similarly, files processed by uuencode
can be placed in pax archives, intermixed with other text files in the
same codeset.
EXAMPLES
None.
RATIONALE
A new algorithm was added at the request of the international community
to parallel work in RFC 2045 (MIME). As with the historical uuencode
format, the Base64 Content-Transfer-Encoding is designed to represent
arbitrary sequences of octets in a form that is not humanly readable. A
65-character subset of the ISO/IEC 646:1991 standard is used, enabling
6 bits to be represented per printable character. (The extra 65th char-
acter, '=', is used to signify a special processing function.)
This subset has the important property that it is represented identi-
cally in all versions of the ISO/IEC 646:1991 standard, including US
ASCII, and all characters in the subset are also represented identi-
cally in all versions of EBCDIC. The historical uuencode algorithm does
not share this property, which is the reason that a second algorithm
was added to the ISO POSIX-2 standard.
The string "====" was used for the termination instead of the end used
in the original format because the latter is a string that could be
valid encoded input.
In an early draft, the -m option was named -b (for Base64), but it was
renamed to reflect its relationship to the RFC 2045. A -u was also
present to invoke the default algorithm, but since this was not histor-
ical practice, it was omitted as being unnecessary.
See the RATIONALE section in uudecode for the derivation of the
/dev/stdout symbol.
FUTURE DIRECTIONS
None.
SEE ALSO
chmod(), mailx, uudecode
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group. In the
event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online
at http://www.opengroup.org/unix/online.html .
IEEE/The Open Group 2003 UUENCODE(1P)
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