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Uuencode is a form of ASCII armor that originated as a Unix program for encoding binary data for transmission over the uucp mail system. The name "uuencode" is derived from "Unix-to-Unix encoding". Since uucp converted characters between various computer's character sets, uuencode was used to convert the data to fairly common characters that were unlikely to be "translated" and thereby destroy the file. The program uudecode reverses the effect of uuencode, recreating the original binary file exactly. uuencode/decode became popular for sending binary files by e-mail and posting to usenet newsgroups etc. However it has now been largely replaced by MIME. ASCII Armor is a term used to describe an encoding process, in which data in a binary format is transformed into a textual format, to allow the data to be successfully transmitted through channels designed only for text messages, such as e-mail or usenet. ... Jump to: navigation, search It has been suggested that List of Unixes be merged into this article or section. ... The word encoding has a number of meanings. ... Look up binary in Wiktionary, the free dictionary Binary may mean: In mathematics and computer science, the binary (base-two) numeral system is a representation for numbers that uses only zeroes and ones as digits. ... UUCP stands for Unix to Unix CoPy, and is a computer program and protocol allowing remote execution of commands and transfer of files, email and netnews between Unix computers not connected to the Internet proper in a Store_and_forward fashion. ... A character encoding is a code that pairs a set of characters (such as an alphabet or syllabary) with a set of something else, such as numbers or electrical pulses. ... Wikipedia does not yet have an article with this exact name. ... Usenet is a distributed Internet discussion system that evolved from a general purpose UUCP network of the same name. ... Multipurpose Internet Mail Extensions (MIME) is an Internet Standard for the format of e-mail. ...

Contents


The encoding process

Uuencoded data starts with a line of the form:

 begin <mode> <file> 

Where <mode> is the file's read/write/execute permissions as three octal digits, and <file> is the name to be used when recreating the binary data.


Uuencode repeatedly takes in a group of three bytes, adding trailing zeros if there are less than three bytes left. These 24 bits are split into four groups of six which are treated as numbers between 0 and 63. Decimal 32 is added to each number and they are output as ASCII characters which will lie in the range 32 (space) to 32+63 = 95 (underscore). ASCII characters greater than 95 may also be used; however, only the six right-most bits are relevant.


Each group of sixty output characters (corresponding to 45 input bytes) is output as a separate line preceded by an encoded character giving the number of encoded bytes on that line. For all lines except the last, this will be the character 'M' (ASCII code 77 = 32+45). If the input is not evenly divisible by 45, the last line will contain the remaining N output characters, preceded by the character whose code is 32+N. Finally, a line containing just a single space (or grave character) is output, followed by one line containing the string "end".


Sometimes each data line has extra dummy characters (often the grave accent) added to avoid problems with mailers that strip trailing spaces. These characters are ignored by uudecode. The grave accent (ASCII 96) can also be used in place of a space character. When stripped of their high bits they both decode to 100000. The grave accent ( ` ) is a diacritic mark used in written Greek until 1982 (polytonic orthography), French, Catalan, Welsh, Italian, Vietnamese, Scottish Gaelic, Norwegian, Portuguese, and other languages. ...


Despite using this limited range of characters, there are still some problems encountered when uuencoded data passes through certain old computers. The worst offenders are computers using non-ASCII character sets such as EBCDIC. EBCDIC (Extended Binary Coded Decimal Interchange Code) is an 8-bit character encoding (code page) used on IBM mainframe operating systems, like z/OS, OS/390, VM and VSE, as well as IBM minicomputer operating systems like OS/400 and i5/OS. It is also employed on various non-IBM...


Sample uuencode

The diagram shows the uuencoding of the three ASCII encoded characters Cat into its uuencoded representation 0V%T. The uuencoding process Image File history File links A depicition of the uuencode process File links The following pages link to this file: Uuencode ...


If the complete uuencoded output of the three ASCII characters Cat might appear as the following

 begin 644 cat.txt #0V%T ` end 

Uuencode table

The following table represents the subset of ASCII characters used by UUEncode and the 6-bit binary string they represent.

Printable
Representation
ASCII Decimal Binary
Representation
Printable
Representation
ASCII Decimal Binary
Representation
(space) 32 000 000 @ 64 100 000
! 33 000 001 A 65 100 001
" 34 000 010 B 66 100 010
# 35 000 011 C 67 100 011
$ 36 000 100 D 68 100 100
% 37 000 101 E 69 100 101
& 38 000 110 F 70 100 110
' 39 000 111 G 71 100 111
( 40 001 000 H 72 101 000
) 41 001 001 I 73 101 001
* 42 001 010 J 74 101 010
+ 43 001 011 K 75 101 011
, 44 001 100 L 76 101 100
- 45 001 101 M 77 101 101
. 46 001 110 N 78 101 110
/ 47 001 111 O 79 101 111
0 48 010 000 P 80 110 000
1 49 010 001 Q 81 110 001
2 50 010 010 R 82 110 010
3 51 010 011 S 83 110 011
4 52 010 100 T 84 110 100
5 53 010 101 U 85 110 101
6 54 010 110 V 86 110 110
7 55 010 111 W 87 110 111
8 56 011 000 X 88 111 000
9 57 011 001 Y 89 111 001
: 58 011 010 Z 90 111 010
; 59 011 011 [ 91 111 011
< 60 011 100 92 111 100
= 61 011 101 ] 93 111 101
> 62 011 110 ^ 94 111 110
? 63 011 111 _ 95 111 111
` 96 (1) 000 000

The grave accent ( ` ) is a diacritic mark used in written Greek until 1982 (polytonic orthography), French, Catalan, Welsh, Italian, Vietnamese, Scottish Gaelic, Norwegian, Portuguese, and other languages. ...

See also

Jump to: navigation, search Base 64 literally means a positional numbering system using a base of 64. ... BinHex, short for binary-to-hexadecimal, is an ASCII armoring system that was used on the Mac OS for sending binary files through E-mail. ... Multipurpose Internet Mail Extensions (MIME) is an Internet Standard for the format of e-mail. ... The title given to this article is incorrect due to technical limitations. ...

References

This article was originally based on material from the Free On-line Dictionary of Computing, which is licensed under the GFDL.

  Results from FactBites:
 
Uuencode - Wikipedia, the free encyclopedia (490 words)
Uuencode is a form of ASCII armor that originated as a Unix program for encoding binary data for transmission over the uucp mail system.
Since uucp converted characters between various computer's character sets, uuencode was used to convert the data to fairly common characters that were unlikely to be "translated" and thereby destroy the file.
Uuencode repeatedly takes in a group of three bytes, adding trailing zeros if there are less than three bytes left.
  More results at FactBites »

 
 

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