Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!eecae!netnews.upenn.edu!rutgers!bellcore!faline!thumper!ulysses!mhuxo!mhuxu!att!cbnews!shurr
From: shurr@cbnews.ATT.COM (Larry A. Shurr)
Newsgroups: comp.sys.ibm.pc
Subject: Re: Execution Order
Keywords: COM EXE BAT
Message-ID: <4283@cbnews.ATT.COM>
Date: 23 Feb 89 19:09:06 GMT
References: <992@expya.cs.exeter.ac.uk>
Reply-To: cbema!las@cbnews.ATT.COM (Larry A. Shurr)
Organization: AT&T Bell Laboratories (actually an AGS consultant)
Lines: 38

In article <992@expya.cs.exeter.ac.uk> sru@cs.exeter.ac.uk (Steve Rush) writes:

[Wants to be able to selectively induce a .EXE file to be executed in
preference to a .COM file having the same name]

>  The reason for asking is that there are several EXE files no our
>machines and I want to do some preprocessing before the actual program
>is run (eg. to check parameters before running 'dangerous' software, ie
>check which drive has been specified before running FORMAT). My idea
>was to write a FILE.COM file which did my preprocessing and then run
>FILE.EXE to run the actual program. But what happens is that it loops,
>continually running my preprocessor !!

I have done something like this in that I have a number of programs
which preprocess the command line and then run a target program passing
the reprocessed command line to it.  As it happens, the preprocessor
programs are .COM files generated from an assembly language template
I wrote and the target programs are (or, were - keep reading) .EXE 
files, but that's not important.  The trick is that I renamed the .EXE 
files to have the extension .XXX.  Since the preprocessor programs 
"exec" the .XXX files, specifying a fixed pathname to the target program,
this works great.  You can do this because the loader doesn't care about
the filename extension, instead it looks at the first two bytes of the
file - if they are the characters "MZ", then it is assumed to be a .EXE
file, otherwise, it is assumed to be a .COM file.  Because the .EXE files
are renamed to a have a new, uninteresting-to-COMMAND.COM extension,
they can never be executed inadvertantly, even if you are in the same
directory in which they are located.

If you do not want to rename the .EXE files - even just to change the 
extension - or to require the files to be on a specific path then this 
method will not help you, sorry.

regards, Larry
-- 
Signed: Larry A. Shurr (att!cbnews!cbema!las or osu-cis!apr!las)
Clever signature, Wonderful wit, Outdo the others, Be a big hit! - Burma Shave
(With apologies to the real thing.  The above represents my views only.)