Batch file programming is nothing but the Windows version of Unix Shell 

Programming. Let's start by understanding what happens when we give a DOS 

command. DOS is basically a file called command.com

It is this file (command.com) which handles all DOS commands that you give at the 

DOS prompt---such as COPY, DIR, DEL etc. These commands are built in with the 

Command.com file. (Such commands which are built in are called internal 

commands.).DOS has something called external commands too such as FORMAT, 

UNDELETE, BACKUP etc.

So whenever we give a DOS command either internal or external, command.com 

either straightaway executes the command (Internal Commands) or calls an external 

separate program which executes the command for it and returns the 

result (External Commands.)

So why do I need Batch File Programs? Say you need to execute a set of commands 

over and over again to perform a routine task like Backing up Important Files, 

Deleting temporary files(*.tmp, .bak , ~.* etc)

then it is very difficult to type the same set of commands over and over 

again. To perform a bulk set of same commands over and over again, Batch files 

are used. Batch Files are to DOS what Macros are to Microsoft Office and are used 

to perform an automated predefined set of tasks over and over again.

So how do I create batch files? To start enjoying using Batch files, you need to 

learn to create Batch files. Batch files are basically plain text files 

containing DOS commands. So the best editor to write your commands in would be 

Notepad or the DOS Editor (EDIT) All you need to remember is that a batch file 

should have the extension .BAT(dot bat)Executing a batch file is quite simple 

too. For example if you create a Batch file and save it with the filename 

batch.bat then all you need to execute the batch file is to type:

C:\windows>batch.bat

So what happens when you give a Batch file to the command.com to execute? 

Whenever command.com comes across a batch file program, it goes into batch 

mode. In the batch mode, it reads the commands from the batch file line by 

line. So basically what happens is, command.com opens the batch file and reads 

the first line, then it closes the batch file. It then executes the command and 

again reopens the batch file and reads the next line from it. Batch files are 

treated as Internal DOS commands.