[windows] Windows batch files: .bat vs .cmd?

As I understand it, .bat is the old 16-bit naming convention, and .cmd is for 32-bit Windows, i.e., starting with NT. But I continue to see .bat files everywhere, and they seem to work exactly the same using either suffix. Assuming that my code will never need to run on anything older than NT, does it really matter which way I name my batch files, or is there some gotcha awaiting me by using the wrong suffix?

everything working in a batch should work in a cmd; cmd provides some extensions for controlling the environment. also, cmd is executed by in new cmd interpreter and thus should be faster (not noticeable on short files) and stabler as bat runs under the NTVDM emulated 16bit environment

Slightly off topic, but have you considered Windows Scripting Host? You might find it nicer.

Still, on Windows 7, BAT files have also this difference : If you ever create files TEST.BAT and TEST.CMD in the same directory, and you run TEST in that directory, it'll run the BAT file.

C:\>echo %PATHEXT%
.COM;.EXE;.BAT;.CMD;.VBS;.VBE;.JS;.JSE;.WSF;.WSH;.MSC

C:\Temp>echo echo bat > test.bat

C:\Temp>echo echo cmd > test.cmd

C:\Temp>test

C:\Temp>echo bat
bat

C:\Temp>

The extension makes no difference.

There are slight differences between COMMAND.COM handling the file vs CMD.EXE.

Here is a compilation of verified information from the various answers and cited references in this thread:

1. command.com is the 16-bit command processor introduced in MS-DOS and was also used in the Win9x series of operating systems.
2. cmd.exe is the 32-bit command processor in Windows NT (64-bit Windows OSes also have a 64-bit version). cmd.exe was never part of Windows 9x. It originated in OS/2 version 1.0, and the OS/2 version of cmd began 16-bit (but was nonetheless a fully fledged protected mode program with commands like start). Windows NT inherited cmd from OS/2, but Windows NT's Win32 version started off 32-bit. Although OS/2 went 32-bit in 1992, its cmd remained a 16-bit OS/2 1.x program.
3. The ComSpec env variable defines which program is launched by .bat and .cmd scripts. (Starting with WinNT this defaults to cmd.exe.)
4. cmd.exe is backward compatible with command.com.
5. A script that is designed for cmd.exe can be named .cmd to prevent accidental execution on Windows 9x. This filename extension also dates back to OS/2 version 1.0 and 1987.

Here is a list of cmd.exe features that are not supported by command.com:

• Long filenames (exceeding the 8.3 format)
• Command history
• Tab completion
• Escape character: ^ (Use for: \ & | > < ^)
• Directory stack: PUSHD/POPD
• Integer arithmetic: SET /A i+=1
• Search/Replace/Substring: SET %varname:expression%
• Command substitution: FOR /F (existed before, has been enhanced)
• Functions: CALL :label

Order of Execution:

If both .bat and .cmd versions of a script (test.bat, test.cmd) are in the same folder and you run the script without the extension (test), by default the .bat version of the script will run, even on 64-bit Windows 7. The order of execution is controlled by the PATHEXT environment variable. See Order in which Command Prompt executes files for more details.

References:

• cmd.exe
• command.com

wikipedia: Comparison of command shells

.cmd and .bat file execution is different because in a .cmd errorlevel variable it can change on a command that is affected by command extensions. That's about it really.

I believe if you change the value of the ComSpec environment variable to %SystemRoot%system32\cmd.exe(CMD) then it doesn't matter if the file extension is .BAT or .CMD. I'm not sure, but this may even be the default for WinXP and above.

RE: Apparently when command.com is invoked is a bit of a complex mystery;

Several months ago, during the course of a project, we had to figure out why some programs that we wanted to run under CMD.EXE were, in fact, running under COMMAND.COM. The "program" in question was a very old .BAT file, that still runs daily.

We discovered that the reason the batch file ran under COMMAND.COM is that it was being started from a .PIF file (also ancient). Since the special memory configuration settings available only through a PIF have become irrelevant, we replaced it with a conventional desktop shortcut.

The same batch file, launched from the shortcut, runs in CMD.EXE. When you think about it, this makes sense. The reason that it took us so long to figure it out was partially due to the fact that we had forgotten that its item in the startup group was a PIF, because it had been in production since 1998.

These answers are a bit too long and focused on interactive use. The important differences for scripting are:

• .cmd prevents inadvertent execution on non-NT systems.
• .cmd enables built-in commands to change Errorlevel to 0 on success.

Not that exciting, eh?

There used to be a number of additional features enabled in .cmd files, called Command Extensions. However, they are now enabled by default for both .bat and .cmd files under Windows 2000 and later.

Bottom line: in 2012 and beyond, I recommend using .cmd exclusively.

Since the original post was regarding the consequences of using the .bat or .cmd suffix, not necessarily the commands inside the file...

One other difference between .bat and .cmd is that if two files exist with the same file name and both those extensions, then:

• entering filename or filename.bat at the command line will run the .bat file

• to run the .cmd file, you have to enter filename.cmd

No - it doesn't matter in the slightest. On NT the .bat and .cmd extension both cause the cmd.exe processor to process the file in exactly the same way.

Additional interesting information about command.com vs. cmd.exe on WinNT-class systems from MS TechNet (http://technet.microsoft.com/en-us/library/cc723564.aspx):

This behavior reveals a quite subtle feature of Windows NT that is very important. The 16-bit MS-DOS shell (COMMAND.COM) that ships with Windows NT is specially designed for Windows NT. When a command is entered for execution by this shell, it does not actually execute it. Instead, it packages the command text and sends it to a 32-bit CMD.EXE command shell for execution. Because all commands are actually executed by CMD.EXE (the Windows NT command shell), the 16-bit shell inherits all the features and facilities of the full Windows NT shell.

a difference:

.cmd files are loaded into memory before being executed. .bat files execute a line, read the next line, execute that line...

you can come across this when you execute a script file and then edit it before it's done executing. bat files will be messed up by this, but cmd files won't.