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.
C:
cd windows
telnet
Now let's analyze the code, the first line tells command.com to go to
the C:Next it tells it to change the current directory to Windows. The
last line tells it to launch the telnet client. You may contradict saying
that the full filename is telnet.exe. Yes you are right, but the .exe
extension is automatically added by command.com. Normally we do not
need to change the drive and the directory as the Windows directory is
the default DOS folder. So instead the bath file could simply contain
the below and would still work.
telnet
Now let's execute this batch file and see what results it shows. Launch
command.com (DOS) and execute the batch file by typing:
C:\WINDOWS>batch_file_name
You would get the following result:
C:\WINDOWS>scandisk
And Scandisk is launched. So now the you know the basic functioning of
Batch files, let' move on to Batch file commands.