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Linux 2.6 - man page for uuencode (linux section 1posix)

UUENCODE(P)			    POSIX Programmer's Manual			      UUENCODE(P)

       uuencode - encode a binary file

       uuencode [-m][file] decode_pathname

       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 per-
       mission bits (in chmod octal or symbolic notation) of the input file and the  decode_path-
       name,  for  re-creation	of  the  file  on  another system that conforms to this volume of
       IEEE Std 1003.1-2001.

       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.

       The following operands shall be supported:


	      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 uude-
	      code is to use standard output. 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.

       See the INPUT FILES section.

       Input files can be files of any type.

       The following environment variables shall affect the execution of uuencode:

       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, Inter-
	      nationalization Variables 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  interna-
	      tionalization variables.

	      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  argu-
	      ments and input files).

	      Determine the locale that should be used to affect the format and contents of diag-
	      nostic messages written to standard error.

	      Determine the location of message catalogs for the processing of LC_MESSAGES .


   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:


       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 concatenated 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 charac-
       ters 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 available at the end of a
       message or encapsulated part of a message. A full encoding quantum shall  always  be  com-
       pleted  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 '='

	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:


       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  con-
       verted 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 character set. It then shall be translated into the cor-
       responding 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 maximum number of octets to be encoded on each line shall  be

       The standard error shall be used only for diagnostic messages.



       The following exit values shall be returned:

	0     Successful completion.

       >0     An error occurred.


       The following sections are informative.

       The  file  is expanded by 35 percent (each three octets become four, plus control informa-
       tion) 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 carried to another machine with the same codeset, it would be per-
       fectly 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 representa-
       tion first. Similarly, files processed by uuencode can be placed in pax	archives,  inter-
       mixed with other text files in the same codeset.


       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 character, '=' , is used
       to signify a special processing function.)

       This subset has the important property that it is represented identically in all  versions
       of the ISO/IEC 646:1991 standard, including US ASCII, and all characters in the subset are
       also represented identically 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 historical practice, it was omitted as being unnecessary.

       See the RATIONALE section in uudecode for the derivation of the /dev/stdout symbol.


       chmod() , mailx , uudecode

       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 orig-
       inal Standard can be obtained online at http://www.opengroup.org/unix/online.html .

IEEE/The Open Group			       2003				      UUENCODE(P)

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