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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Hacking Truth: While creating a batch file, one thing that you need to keep in

mind is that the filename of the batch file should not use the same name as a

DOS command. For example, if you create a batch file by the name dir.bat and then

try to execute it at the prompt, nothing will happen.

This is because when command.com comes across a command, it first checks to see

if it is an internal command. If it is not then command.com checks if it a .COM,

.EXE or .BAT file with a matching filename.

All external DOS commands use either a .COM or a .EXE extension, DOS never

bothers to check if the batch program exits.

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Now let's move on to your first Batch file program. We will unlike

always(Normally we begin with the obligatory Hello World program) first take up

a simple batch file which executes or launches a .EXE program. Simply type the

following in a blank text file and save it with a .BAT extension.



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