Communication Commands uuencode(1C)
NAME
uuencode, uudecode - encode a binary file, or decode its
encoded representation
SYNOPSIS
uuencode [source-file] decodepathname
uuencode [-m] [source-file] decodepathname
uudecode [-p] [encoded-file]
uudecode [-o outfile] [encoded-file]
DESCRIPTION
These commands encode and decode files as follows:
uuencode
The uuencode utility converts a binary file into an encoded
representation that can be sent using mail(1). It encodes
the contents of source-file, or the standard input if no
source-file argument is given. The decodepathname argument
is required. The decodepathname is included in the encoded
file's header as the name of the file into which uudecode is
to place the binary (decoded) data. uuencode also includes
the permission modes of source-file (except setuid, setgid,
and sticky-bits), so that decodepathname is recreated with
those same permission modes.
uudecode
The uudecode utility reads an encoded-file, strips off any
leading and trailing lines added by mailer programs, and
recreates the original binary data with the filename and the
mode specified in the header.
The encoded file is an ordinary portable character set text
file; it can be edited by any text editor. It is best only
to change the mode or decodepathname in the header to
avoid corrupting the decoded binary.
OPTIONS
The following options are supported:
uuencode
-m Encodes source-file using Base64 encoding and sends it
to standard output.
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Communication Commands uuencode(1C)
uudecode
-o outfile Specifies a file pathname that should be used
instead of any pathname contained in the input
data. Specifying an outfile option-argument of
/dev/stdout indicates standard output.This
allows uudecode to be used in a pipeline.
-p Decodes encoded-file and sends it to standard
output. This allows uudecode to be used in a
pipeline.
OPERANDS
The following operands are supported by uuencode and
uudecode:
uuencode
decodepathname The pathname of the file into which the
uudecode utility will place the decoded
file. If there are characters in
decodepathname that are not in the port-
able filename character set, the results
are unspecified.
source-file A pathname of the file to be encoded.
uudecode
encoded-file The pathname of a file containing the output
of uuencode.
USAGE
See largefile(5) for the description of the behavior of
uuencode and uudecode when encountering files greater than
or equal to 2 Gbyte ( 2^31 bytes).
ENVIRONMENT VARIABLES
See environ(5) for descriptions of the following environment
variables that affect the execution of uuencode and
uudecode: LANG, LCAL, LCTYPE, LCMESAGES, and NLSPATH.
OUTPUT
stdout
uuencode Base64 Algorithm
The standard output is a text file, encoded in the character
set of the current locale, that begins with the line:
begin-base64 %s %s0 mode, decodepathname
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Communication Commands uuencode(1C)
and ends with the line:
====
In both cases, the lines have no preceding or trailing blank
characters.
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 is formed by con-
catenating three 8-bit input groups. Each 24-bit input group
is then treated as four concatenated 6-bit groups, each of
which is translated into a single digit in the Base64 alpha-
bet. When encoding a bit stream by means of the Base64
encoding, the bit stream is presumed to be ordered with the
most-significant bit first. That is, the first bit in the
stream is the high-order bit in the first byte, and the
eighth bit is 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 the following table.
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 is placed in the out-
put string.
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Communication Commands uuencode(1C)
The output stream (encoded bytes) is represented in lines of
no more than 76 characters each. All line breaks or other
characters not found in the table are ignored by decoding
software (see uudecode).
Special processing is performed if fewer than 24 bits are
available at the end of a message or encapsulated part of a
message. A full encoding quantum is always completed at the
end of a message. When fewer than 24 input bits are avail-
able in an input group, zero bits are 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 are set to the equals (=) 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 is an integral multiple of four
characters with no '= ' padding.
2. The final quantum of encoding input is exactly 16
bits. Here, the final unit of encoded output is
three characters followed by one '=' padding char-
acter.
3. The final quantum of encoding input is exactly 8
bits. Here, the final unit of encoded output is 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 is a text file (encoded in the character
set of the current locale) that begins with the line:
begin %s %s\n, mode, decodepathname
and ends with the line:
end\n
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Communication Commands uuencode(1C)
In both cases, the lines have no preceding or trailing blank
characters.
The algorithm that is used for lines 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 are converted to characters by adding a value of 0x20
to each octet, so that each octet is in the range 0x20-0x5f,
and each octet is assumed to represent a printable charac-
ter. Each octect is then 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
the codeset were EBCDIC.
Where the bits of two octets are combined, the least signi-
ficant bits of the first octet are shifted left and combined
with the most significant bits of the second octet shifted
right. Thus, the three octets A, B, C are 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 are then 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 maximum number of octets to be
encoded on each line is 45.
EXIT STATUS
The following exit values are returned:
0 Successful completion.
>0 An error occurred.
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ATRIBUTES
See attributes(5) for descriptions of the following attri-
butes:
ATRIBUTE TYPE ATRIBUTE VALUE
Availability SUNWesu
Interface Stability Standard
SEE ALSO
mail(1), mailx(1), uucp(1C), uux(1C), attributes(5),
environ(5), largefile(5), standards(5)
NOTES
The size of the encoded file is expanded by 35% (3 bytes
become 4, plus control information), causing it to take
longer to transmit than the equivalent binary.
The user on the remote system who is invoking uudecode (typ-
ically uucp) must have write permission on the file speci-
fied in the decodepathname.
If you invoke uuencode and then execute uudecode on a file
in the same directory, you will overwrite the original file.
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