A new character on the command line

[Jerry Peek]

I'm writing a program and I've got a question about the command line
syntax for invoking it.  The program, "zrefile", moves MH Mail messages
in and out of an archive file.  The user has to give the archive
filename on the command line.  Other MH programs use "+foldername" and
"@foldername" on the command line.  I'd like to use the same style, but
a different marker character for the archive file than "+" or "@".

I want this program to work from as many shells as possible, and not
conflict with some upcoming standard.  So, for instance, I can't use
"!archivename" on the command line because csh treats !xxx as a history
event.  So, I'm looking for marker characters to use that don't confuse
ANY shell.  They should not need quoting.  I've got four ideas:  % : _ =
For example, if the archive is named "archivename", a user might type:
	zrefile 1 3 5 %archivename
or	zrefile 1 3 5 :archivename

I'd rather not use a "required flag" like "-a archivename".
Opinions, anybody?  Thanks a lot.

--Jerry Peek; Syracuse University Academic Computing Services; Syracuse, NY
  jdpeek at rodan.acs.syr.edu///JDPEEK at SUVM.BITNET///GEnie: J.PEEK1
  +1 315 443-3995