uuencode(1)uuencode(1)NAME
uuencode, uudecode - encode/decode a binary file for transmission by
mailer
SYNOPSIS
[source_file] remotedest
outfile] [encoded_file]
DESCRIPTION
and can be used to send a binary file to another machine by means of
such services as or (see elm(1), mailx(1), and uucp(1)).
takes the named source file (default standard input) and produces an
encoded version on the standard output. The encoding uses only print‐
ing ASCII characters, includes the original mode of the input file, and
preserves the value of the remotedest argument which is the intended
name of the file when it is restored later on the remote system.
reads an encoded file (the encoded_file argument), ignores any leading
and trailing lines added by mailers, and recreates the original file
with the specified mode and name.
The encoded file is an ordinary ASCII text file and can be edited with
any text editor to change the mode or remote name.
Options and Arguments
recognizes the following command-line option:
Encode the input file using the MIME Base64 algorithm. If is
not specified, the historical algorithm encodes the input.
recognizes the following command-line option and argument:
Specifies the pathname of the file that holds the decoded out‐
put. This file is not the same as remotedest which was speci‐
fied at the time of encoding the file.
uuencode Base64 Algorithm
The encoded file is a text file, encoded in the character set of the
current locale (the portable character set). The file begins with the
line:
and ends with the line:
Both of the above lines have no preceding or trailing blank characters.
The encoding process represents each 24-bit group of input bits as out‐
put strings of four encoded characters. Proceeding from left to right,
each 24-bit input group is formed by concatenating three 8-bit input
groups. Each such 24-bit input group is then treated as four concate‐
nated 6-bit groups, each of which would be translated into a single
digit in the Base64 alphabet 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
When encoding a bit stream via 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 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 line of the encoded output can have only 76 characters or less.
If there are less than 24 bits available at the end of a message or
encapsulated part of a message, zero bits are added (on the right) to
form an integral number of 6-bit groups. Output character positions
that are completely made of the padded zero bits are set to the equal
character
Because all Base64 input is an integral number of octets, only the fol‐
lowing cases can arise at the end of an input bit stream:
1. If the final quantum of encoding input is an integral multi‐
ple of 24 bits, the final unit of encoded output is an inte‐
gral multiple of 4 characters with no padding character.
2. If the final quantum of encoding input is exactly 16 bits,
the final unit of encoded output is three characters followed
by one padding character.
3. If the final quantum of encoding input is exactly 8 bits, the
final unit of encoded output is two characters followed by
two padding characters.
All line breaks and other non-Base64 characters are ignored by A termi‐
nating evaluates to nothing and denotes the end of the encoded data.
uuencode Historical Algorithm
The encoded file is a text file, encoded in the character set of the
current locale (the portable character set). It begins with the line:
and ends with the line:
Both of the above lines have no preceding or trailing blank characters.
This algorithm takes three octets as input and writes four characters
of output by splitting the input at 6-bit intervals. The four 6-bit
groups make four octets each of which contain 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].
That is, it is assumed to represent a printable character in the
ISO/IEC 646:1991 standard encoded character set. Each octet is then
translated into the corresponding character code for the codeset in use
in the current locale before writing the encoded output.
When the bits of two octets are combined, the least significant 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 following 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. Each line
of the encoded output has only 45 characters or less.
EXAMPLES
The following example encodes a file (using the historical algorithm)
with as the intended name on the remote system and saves the output in
Similarly, the following example uses the option to encode a file
(using the MIME Base64 algorithm) with as the intended name on the
remote system and saves the output in
The following example shows how to encode and send a compiled program
to user
After receiving the mail message, user can decode the program to a file
with the same name as the original file by first saving the message in
a file and executing the command:
Similarly, the user can also decode the program to a file named by
first saving the message in a file and executing the command:
WARNINGS
The file is expanded by 35% (three bytes become four plus control
information) causing it to take longer to transmit.
The user on the remote system who is invoking (often must have write
permission for the specified file.
If an encoded file has the same name as the destination name specified
in it, starts overwriting the encoded file before decoding is com‐
pleted.
SEE ALSOelm(1), mail(1), mailx(1), shar(1), uucp(1), uux(1), uuencode(4).
STANDARDS CONFORMANCEuuencode(1)
