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Unix program for encoding binary data as ASCII. Uuencode was
originally used with uucp to transfer binary files over serial
lines which did not preserve the top bit of characters but is
now used for sending binary files by e-mail and posting to
Usenet newsgroups etc. The program uudecode reverses the
effect of uuencode, recreating the original binary file
Uuencoded data starts with a line of the form
begin mode file
where mode is the files 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 ouput as ASCII characters which will
lie in the range 32 (space) to 32+63 = 95 (underscore). Each
group of sixty ouptut characters (corresponding to 45 input
bytes) is output as a separate line preceded by an 'M' (ASCII
code 77 = 32+45). At the end of the input, if there are N
output characters left after the last group of sixty and N@#0
then they will be preceded by the character whose code is
32+N. Finally, a line containing just a single space is
output, followed by one containing just "end".
Sometimes each data line has an extra dummy character added to
avoid problems which mailers that strip trailing spaces.
These characters are ignored by uudecode.
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.
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