23 Nov, 2008

Batch File Programming

     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.

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