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uuexplode - decode multiple and/or multipart uuencoded files to their target files


uuexplode [-hqslcfw] [-t dirname] [filename, filename...]


uuexplode is a "smart", fast uudecoder that will decode one or more files consisting of complete uuencoded files. The target files can be written in any user specified directory or in current. It is upward compatible with uudecode(1) provided that the encoder program used to create the input to uuexplode has more or less followed the format described in uuencode(5) . See Technical Notes below.

If no filename(s) is supplied, input is read from stdin. It can also write to stdout and hence act as a proper filter.

uuexplode automatically ignores lines that do not appear to be part of the uuencoded file. This is particularly useful in uudecoding files that have been concatenated from several email or news postings without stripping off the headers or otherwise editing extraneous content. A lot of effort was put into ensuring that erroneous target files are not written, several error and warning messages are written to stdout when uuexplode finds something in the input it doesn’t accept or just finds strange. The messages are meant to be self explanatory and contain line numbers in the input file. Note that when warnings are issued, the output is still most likely correct.


Print usage message stdout.
Quiet. Do not print any diagnostics, errors or warning messages - no matter what goes wrong.
Write data to stdout instead of to the target file. Only the very first target file found in the input will be written, then uuexplode exits. By the "first" file is meant the first file actually containing any decodable uucode at all. This file may not be in the first input file if there are more than one. All warning/error messages go to stderr so there is no need to use -q with -s.
Lenient mode. This allows for the short data line, the one not beginning with an "M"at the end of a uucode block, to have a non-standard length. Use this as a second attempt if a target file seems to come out corrupted even if no warnings were printed during decoding. Note: -l causes the security of uucode recognition to drop quite considerably, do not use casually.
Careless mode. This stops the checks for illegal characters in the short data line. Its main use is in conjunction with -f when it allows decoding of uucode in the character range [>..}] that some non-standard encoders produce. This kind of code is transparent to a "dumb" uudecode program. Never use this option unless you know you have non-standard uucode.
Fast mode. This stops the checks for illegal characters in the normal uucode data lines. It makes the decoding go faster, but not significantly (in fact probably not even noticably). Normally this would only be used with -c if you know you have uucode with a non-standard character range. The sequrity of uucode recognition with -f -c is much lower than normal.
Overwite. Without this, uuexplode will refuse to overwrite a target file that already exists.
-t dirname
Target directory. The named directory does not have to exist, it will be created. Should this fail, uuexplode exits and no target files will be written. Without -t, the target files always end up in current directory.

Technical Notes

This is for advanced users who know the uucode format well and want to know more about what uuexplode accepts as valid uucode. A number of constraints are put on it:
  1. The first line after the ’begin’-line is a uucode line if all characters are valid, it begins with [SPC..M,’] and the length is not totally absurd with respect to what the first char was.
  2. There is at least a \n behind each uucode line. There may be a \r also.
  3. If there are extra chars at the end of the data lines it is present in all lines, even the last ‘-line. And always the same number of chars.
  4. There are no extra chars behind the ’end’-line except \n or \r\n
  5. The normal uucode lines are always 45 bytes (60 chars) and have ’M’ as length indicator. A "standard" uudecode program does not care about this at all.
  6. No valid uucode contains ASCII > ’a’. Note that one can also use the range [>..}] since bit 6 of the chars are unused. Again a "standard" uudecode program will happily decode such data, uuexplode will only do this with -f -cc. There are uuencoders (e.g. on the Macintosh) that produce such uucode.
  7. The end of a uucode block resides in the same input file (or stdin) as the corresponding ’begin’-line.
  8. All parts belonging to the same target file(s) are in correct order in the input.
  9. The input contains no characers with ASCII code less than 32.

A small list of capabilities concerning garbage lines:
No assumptions whatsoever are made about the format of a garbage line.
Handles garbage between all the last three lines of a uucode block.
Handles bogus SPACE/‘ lines between parts (and at the end) of the same block.
Handles bogus short data lines in the middle of a uucode block.
Handles short or even empty uucode blocks correctly.
Tolerates optional checksum/"guard" character(s) at the end of data lines.
Tolerates SPACE or ‘ as zero-code. The empty-line can be SPACE, ‘ or ‘‘.


If all decoding went well, the returncode is 0. Otherwise it is the logical OR of the following values:
1   At least one warning was issued
2   At least one error occurred, possibly casuing a target file not to be created
4   A target file already existed (only if -w was not actice)


Some of the warnings and errors are not quite as self explanatory as one would wish. A user that does not know the uucode format and does not want to know, may not be able to understand why the file he tried to decode failed.

The options -c and -l require at least rudimentary knowledge of the uucode format to be really useful.

There is no proper standard formally specifying the format of uucode or what a uudecode algorithm shall accept as valid input. This program tries to be lenient enough to accept all the common variants while still being as pedantic as possible. There are variants of uuencoders out there producing (at least capable of producing) uucode that uuexplode does not accept. A present no such commonly used uuencoders are known to me.

The algorithms used to detect valid uucode are not based on proper statistical analysis of uuencoded data with garabage lines in it. Instead, some fairly rigid theoretical analysis, partly based on what kind of garbage normally occur in Email and News postings (but not limited to those) was done. It may not work as well with totally random garbage interleaved with the uucode.

See Also

uuencode(5) , uuencode(1) , uudecode(1)


Michael Bergman (

Uuexplode was originally based on a program called "kiss", written by Kevin Young. This program was part of a collection of uucode tools called uuxfer. The actual decoding function that decodes one line of uucode is also written by Kevin and altough all the other code has been almost completely rewritten this remains unaltered.

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