xargs

[Richard A. O'Keefe]

Having had rather more core-dumps from xargs(1) {on lots of different
machines} than I really care for, I decided that it was time to write
my own.  Deciding that the thing to do was to make it as exactly
compatible as I could, only working, I turned to the SVID to find out
just what xargs is supposed to do.  I find the XARGS(SD_CMD) section
of the SVID remarkably obscure.  For example, are empty lines to be
discarded in the sense that they aren't *counted* by the -l option,
or are they to be discarded only in the sense that they don't
contribute any arguments?  {Don't suggest running the program; what I
want to know is what it is *supposed* to do.}  If a line has a space
or tab before the new-line, is it still counted by -l?  What about
new-lines quoted by \ ?  We are told that blanks and tabs are allowed
in arguments, if quoted, but what about new-lines?

Then too, what is the significance of the magic numbers?
 -- why will "-i" accept only five *arguments* containing replstr,
    given that any one argument may contain any number of instances
    of replstr?  Would anything break if this limit were raised?
 -- why may constructed arguments grow to only 255 characters
    (apart from the fact that it crashes if you try a bigger number)?
    The exec() family is happy with much longer arguments than that!
    This is particularly painful in BSD systems, where a single
    file-name can be 1023 characters long...
 -- Why is the maximum total size of an argument list 470 characters?
    See above comment on file names.

The XARGS(SD_CMD) section also says that "xargs will terminate if ...
it receives a return code of -1 from ... command".  This is bizarre,
because elsewhere the SVID makes it clear that the exit status of a
command is ((W)>>8)&0377, where W is the result WAIT(BA_OS) gets.
Does the xargs section mean 255?  Or 1?  Or any non-zero value (which
would be consistent with everthing else)?

So, is there a clear description of xargs anywhere?