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OpenDarwin 7.2.1 - man page for uuencode (opendarwin section 5)

uuencode(5)			       File Formats Manual			      uuencode(5)

       uuencode file format

       The command generates files in a format that allows them to be successfully 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 "filename.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 characters. 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.

       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 repre-
       sent zero. Many (arguably broken) mailers and transport	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 character 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 character sequences that may naturally occur in
       the encoding (such as sequences of dashes ("---")) to divide sections.

       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)

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