Autoconf Transforms

[Tom Browder]

I am trying to use some raw shell commands in my 'configure.ac' file
and find that some constructs are not permitted without some care,
e.g., regex classes, where 's/[^0-9]//' becomes 's/^0-9//' unless one
doubles the square braces like so 's/[[^0-9]]//' in which case one of
each pair is stripped away to get the desired form in the resulting
'configure' file.  But that may not be the correct way to handle it.

I guess the manual is trying to tell me that implicitly by discussing
the m4 processor parsing rules, but I haven't yet found an explicit
warning to that effect about use of shell commands (except the
warnings about portable shell programming and recomended non-use of
the negated character class form).

Are there more such constructs I should be on the lookout for?  Have I
missed somthing in the manual?

Thanks.

-Tom