Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!ames!killer!jls
From: jls@killer.DALLAS.TX.US (Jerome Schneider)
Newsgroups: comp.sys.ibm.pc
Subject: Re: Execution Order
Summary: Command.com sets the search order
Keywords: COM EXE BAT
Message-ID: <7237@killer.DALLAS.TX.US>
Date: 20 Feb 89 04:41:34 GMT
References: <992@expya.cs.exeter.ac.uk> <22@dbase.UUCP>
Organization: The Unix(R) Connection, Dallas, Texas
Lines: 37

In article <22@dbase.UUCP>, marc@dbase.UUCP (Marc Schifer) writes:
> In article <992@expya.cs.exeter.ac.uk>, sru@cs.exeter.ac.uk (Steve Rush) writes:
> >   I have a question about execution order in MSDOS. I beleive that
> > commands in MSDOS are executed in the order .COM .EXE .BAT so if there
> > are several files in the directory with the same name but with
> > different extensions it is the .COM file that would be executed.
> > [question about circumventing this is deleted]
 
> >   Thanks in advance for any suggestions.
> >                    Steve
>     Try renaming the .EXE file to something else (ie XFILE.EXE)
>     this way you eliminate the looping.(of course it still allows
>     someone to execute the original file on its own.)  IF your 
>     com file is calling the exe file internaly you may try using 
>     some nonstandard characters in the second files name to 
>     slow down the average user from accessing the file.
> 	     hope this helps
> 		   marc

Steve's observation about the COM EXE BAT search order is correct.  When
command.com tries to run a program, the extension is stripped off and the
three extensions are appended, one at a time, while the PATH is searched
for a matching file.  The first match found is the file executed.  The
three extensions are stored near the very end of the COMMAND.COM file and
it might be possible to hack command.com to alter the search order, but
your problem with the PATH search sequence will reamain.  

As a side note, the EXE extension on a file is not really used by the
loader -- a magic number in the first two bytes identifies a relocatable
module, even if it is called foo.bar.  However, this trick is probably
valid only from a spawn() call that bypasses COMMAND.COM.  It would
appear, then, that DOS will frustrate any attempts to modify the search
sequence.  

-- 
Jerome Schneider              UUCP: killer!jls.DALLAS.TX.US (guest account)
Aspen Technology Group        Ft. Collins, CO    Voice: (303) 484-8466