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uuencode(5)                                                        uuencode(5)




NAME

       uuencode file format


DESCRIPTION

       The command generates files in a format that allows them to be success-
       fully transferred by systems which strip the high  bit  from  an  8-bit
       byte.  decodes uuencoded files.


       The  uuencode file format consists of three sections: header, body, and
       trailer.  The header is a line is of the form:


       begin 644 "filename.ext"


       where "644" is a -format permissions  byte  for  the  file  and  "file-
       name.ext" is the name of the encoded file.


       The  body  section  is  the  encoded representation of the source file.
       Three bytes of input file data are encoded into four  bytes  of  output
       data.

       The 24 input bits are divided up into four pieces of six bits each. The
       integer value 32 (the ASCII value for the space character) is added  to
       each of these pieces to move them outside of the range of control char-
       acters. To avoid using the space character in the encoding, pieces with
       value  zero  are  encoded  using  backquote (ASCII value 96) instead of
       zero. The resulting character is one of  the  this  set  (ASCII  values
       96,33-95):



       A  line  itself  contains  three  segments: a length character (encoded
       using the "add a space" algorithm described above),  the  body  of  the
       line,  typically  (although  not  required  to be) 60 output characters
       long, representing 45 input bytes, and (of  course)  a  linefeed.   The
       length  character specifies the number of valid input bytes on the line
       (so, for a line which is 60 encoded bytes, the length  value  would  be
       45).   Decoding  programs  should  decode no further than the specified
       length on a single line.


       The trailer, which must exist, consists of  a  single  backquote  ("`",
       ASCII 96) character on a line by itself, directly followed by on a line
       by itself.


       is the canonical filename extension for uuencoded files.



BUGS

       uudecode does not read all permutations of the file format described in
       this man page.


       Ancient  versions  of uuencode used a space character (ASCII 32) in the
       encoding to represent zero. Many (arguably broken) mailers  and  trans-
       port  agents  stripped, rewrapped, or otherwise mangled this format, so
       the space was later changed to the backquote, ASCII  96.  Decoders  may
       attempt  to read the older format if they wish, though it's unlikely to
       be encountered in practice at this point in time.


       The uuencode encoding method is highly  ASCII-centric.  In  particular,
       the  character  set  used  doesn't  work  well on EBCDIC-based systems.
       (EBCDIC, generally used by IBM mainframes, is an old alternative  char-
       acter encoding; most computers use ASCII instead).


       Many variants of uuencode on various platforms generate different forms
       of line checksums, using to represent the checksum one or more  encoded
       characters  after  the last counted character in a line.  Because these
       formats are different and impossible to distinguish  (with  certainty),
       such characters should be ignored by decoding implementations.


       The  uuencode  encoding  format  has no provisions for segmented files.
       Writers of segmenting utilities should be careful to avoid using  char-
       acter  sequences  that  may  naturally  occur  in the encoding (such as
       sequences of dashes ("---")) to divide sections.



SEE ALSO

       The MIME Base64 encoding (documented in  RFC  2045)  is  a  consistent,
       cross-platform-savvy  message encoding which should be used in place of
       UUEncode wherever possible.


       The Unix-Hater's Handbook (IDG, 1994) identifies the folly of the older
       zero-encoded-as-space versions of uuencode.




Apple Computer, Inc.               May, 2001                       uuencode(5)

Mac OS X 10.7 - Generated Wed Aug 24 20:32:13 CDT 2011
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