PATHEXT

PATHEXT can be used to select the extensions to look for when searching 
the PATH for an executable file.  It consists of a list of extensions, 
separated by semicolons. For example, to replicate the default extension 
list used by CMD.EXE: 

     set pathext=.com;.exe;.btm;.cmd;.bat

PATHEXT is ignored unless the PathExt setting is set to Yes in CMD.INI. 
Once PATHEXT is enabled the standard path search for .COM, .EXE, .BTM, 
.CMD, and .BAT files is replaced by a search for files with the extensions 
listed in PATHEXT, in the order listed there. 

Enabling PATHEXT affects only the standard path search, it does not affect 
the subsequent searches for files with executable extensions.  PATHEXT is 
supported for compatibility reasons but should not generally be used as a 
substitute for executable extensions, which are much more flexible.  For 
more details on path searches, see the PATH command. 

CAUTION:  If you set PathExt = Yes in CMD.INI and then fail to set the 
PATHEXT variable, path searches will fail as there will be no extensions 
for which to search!