Executable Extensions

The syntax for creating an executable extension is: 

        set .ext=command [options]

This tells CMD.EXE to run the specified command whenever you name a file 
with the extension .ext at the prompt. 

.EXT is the executable file extension; command is the name of the internal 
command, external program, alias, or batch file to run; and [options] are 
any command-line startup options you want to specify for the program, 
batch file, or alias. 

Normally, when you type a filename (as opposed to an alias or internal 
command name) as the first word on the command line, CMD.EXE looks for a 
file with that name to execute.  The file's extension may be .EXE or .COM 
to indicate that it contains a program, it may have a batch file extension 
like .BTM, or the file's contents may indicate that it is executable.  (To 
change the default list of extensions see the PATHEXT environment variable 
and the PathExt setting in CMD.INI.) 

You can add to the default list of extensions, and have CMD.EXE take the 
action you want with files that are not executable programs or batch 
files.  The action taken is always based on the file's extension.  For 
example, you could start your text editor whenever you type the name of a 
.DOC file, or start your database manager whenever you type the name of a 
.DAT file. 

You can use environment variables to define the internal command, external 
program, batch file, or alias to run for each defined file extension.  To 
create an executable extension, use the SET command to create a new 
environment variable.  An environment variable is recognized as an 
executable extension if its name begins with a period. 

For example, if you want to run a word processor called EDITOR whenever 
you type the name of a file that has an extension of .EDT, you could use 
this command: 

        [c:\] set .edt=c:\edit\editor.exe

If the command specified in an executable extension is a batch file or 
external program, CMD.EXE will search the PATH for it if necessary. 
 However, you can make sure that the correct program or batch file is 
used, and speed up the executable extension, by specifying the full name 
including drive, path, filename, and extension. 

Once an executable extension is defined, any time you name a file with 
that extension the corresponding program, batch file, or alias is started, 
with the name of your file passed to it as a parameter. 

The following example defines B.EXE (the Boxer text editor) as the 
processor for .MAK files: 

        [c:\] set .mak=c:\boxer\b.exe -s

With this definition, if you have a file named INIT.MAK in the current 
directory and enter the command: 

        [c:\source] init

CMD.EXE will execute the command: 

        c:\boxer\b.exe -s c:\source\init.mak

Notice that the full pathname of INIT.MAK is automatically included.  If 
you enter parameters on the command line, they are appended to the end of 
the command.  For example, if you changed the above entry to: 

        [c:\source] init -w

the command processor would execute the command: 

        c:\boxer\b.exe -s c:\source\init.mak -w

In order for executable extensions to work, the command, program, batch 
file, or alias must be able to interpret the command line properly.  For 
example, if a program you want to run doesn't accept a file name on its 
command line as shown in these examples, then executable extensions won't 
work with that program. 

Executable extensions may include wildcards, so you could, for example, 
run your text editor for any file with an extension beginning with T by 
defining an executable extension called .T*.  Extended wildcards (e.g., 
DO[CT] for .DOC and .DOT files) may also be used. 

The search for executable files starts in the current directory, then 
proceeds to each subdirectory specified by the PATH environment variable 
(if a "." is used in the PATH the current directory is not searched first; 
see the PATH command for details). 

You may need to take this search order into account when using executable 
extensions.  Using the .MAK example above, if you had a file named 
FORMAT.MAK in the current directory and entered the command FORMAT A:, 
your command would run the Boxer editor specified by the executable 
extension, instead of finding the standard OS/2 FORMAT command as you 
perhaps intended.  You can get around this by remembering that the OS/2 
FORMAT command is in the file FORMAT.COM.  If you entered the command 
FORMAT.COM A: then the .MAK executable extension would not be checked, and 
the search would continue until it found the FORMAT.COM file. 

To remove an executable extension, use the UNSET command to remove the 
corresponding variable.