HACKING TRUTH:

We can also check for more than one file at a time,
in the following way:
IF EXIST c:\autoexec.bat IF EXIST c:\autoexec.bak ECHO Both Exist
****************** 

We can check to see if a file does not exist in the same way, the basic
syntax now becomes:

IF NOT EXIST FILENAME Command
For Example,
IF NOT EXIST c:\mystylepro.doc ECHO It doesn't Exist
**************** 

HACKING TRUTH: How do you check for the existence of directories?
No something like IF C:\windows EXISTS ECHO Yes does not work. In
this case we need to make use of the NULL device. The NULL device is
basically nothing, it actually stands for simply nothing. Each directory
has the NULL device present in it. (At least DOS thinks so.) So to
check if c:\windows exits, simply type:
IF EXIST c:\windows\nul ECHO c:\Windows exists.
One can also check if a drive is valid, by giving something like:
IF EXIST c:\io.sys ECHO Drive c: is valid.
****************
Comparing Strings to Validate Parameters
The basic syntax is:
IF [NOT] string1==string2 Command
Now let's make our scripts intelligent and make them perform a task
according to what parameter was passed by the User. Take the
following snippet of code for example,
@ECHO off
IF %1==cp GOTO COPY
GOTO DEL
:COPY
Copy %2 a:
GOTO :END
:DEL
Del %2
:END
This example too is pretty much self explanatory. The IF Statement
compares the first parameter to cp, and if it matches then DOS is sent
to read the COPY label else to the DEL label. This example makes use
of two parameters and is called by passing at least two parameters.
We can edit the above example to make DOS check if a parameter was
passed or not and if not then display an error message. Just add the
following lines to the beginning of the above file.
@ECHO OFF
IF "%1" == "" ECHO Error Message Here
If no parameter is passed then the batch file displays an error
message. Similarly we can also check for the existence of the second
parameter.
This command too has the NOT clause.

IF: CONDITIONAL BRANCHING

The If statement is a very useful command which allows us to make the
batch files more intelligent and useful. Using this command one can make
the batch programs check the parameters and accordingly perform a
task. Not only can the IF command check parameters, it can also checks
if a particular file exists or not. On top of all this, it can also be used
for the conventional checking of variables (strings).
Checking If a File Exists Or Not
The general syntax of the IF command which checks for the existence
of a file is the following:
IF [NOT] EXIST FILENAME Command
This will become clearer when we take up the following example,
IF EXIST c:\autoexec.bat ECHO It exists

This command checks to see if the file, c:\autoexec.bat exists or not.
If it does then it echoes or prints the string 'It exists'. On the other
hand if the specified file does not exist, then it does not do anything.
In the above example, if the file autoexec.bat did not exist, then
nothing was executed. We can also put in the else clause i.e. If the File
exists, do this but if it does not exists, by using the GOTO command.
Let's consider the following example to make it more clear:
@echo off
IF EXIST C:\anil.doc GOTO ANIL
Goto end
:ANIL
ECHO ANIL
:end
The IF statement in this code snippet checks to see if there exists a
file, c:\anil.doc. If it does then DOS is branched to :ANIL and if it
does not, then DOS goes on to the next line. The next line branches
DOS to :end. The :end and :ANIL in the above example are called
labels. After the branching the respective echo statements take over.

SHIFT: Infinite Parameters

Sometimes your batch file program may need to use more than nine
parameters at a
time.(Actually you would never need to, but at least you are sure you
can handle
it if you need to.)To see how the SHIFT command works, look at the
following
snippet of code:
@ECHO OFF
ECHO The first Parameter is %1
ECHO.
SHIFT
ECHO The Second Parameter is %1
ECHO.
SHIFT
ECHO The Second Parameter is %1
Now execute this batch file from DOS and see what happens.
C:\windows>batch_file_name abc def ghi 

The first Parameter is abc
The Second Parameter is def
The Second Parameter is ghi
How does it work? Well, each SHIFT command shuffles the parameters
down one position. This means that after the first SHIFT %1 becomes def, %2
becomes ghi
and abc is completely removed by DOS. All parameters change and move
one position
down.
Both normal parameters (%1 , % 2 etc) and the SHIFT command can be
made more
efficient by grouping them with the IF conditional statement to check
the
parameters passed by the User.
THE FOR LOOP
The syntax of the FOR LOOP is:
FOR %%PARAMETER IN(set) DO command
Most people change their mind about learning Batch Programming when
they come
across the syntax of the For Command. I do agree that it does seem a
bit weird,
but it is not as difficult as it appears to be. Let's analyze the various
parts
of the For command. Before we do that look at the following example,
@ECHO OFF
CLS
FOR %%A IN (abc, def, xyz) DO ECHO %%A
Basically a FOR LOOP declares a variable (%%A) and assigns it different
values
as it goes through the predefined set of values(abc, def, xyz) and each
time
the variable is assigned a new value, the FOR loop performs a
command.(ECHO %%A)

The %%A is the variable which is assigned different values as the loop
goes
through the predefined set of values in the brackets. You can use any
single
letter character after the two % sign except 0 through 9.We use two
%'s as DOS
deletes each occurrence of a single % sign in a batch file program.
The IN(abc, def, xyz) is the list through which the FOR loop goes. The
variable
%%a is assigned the various values within the brackets, as the loop
moves. The
items in the set(The technical term for the set of values within the
brackets)
can be separated with commas, colons or simply spaces.
For each item in the set(The IN Thing) the FOR loop performs whatever
command is
given after the DO keyword.(In this example the loop will ECHO %%A)
So basically when we execute the above batch file, the output will be:
abc
def
xyz
The FOR loop becomes very powerful if used along with replaceable
parameters. Take
the following batch file, for example,
@ECHO OFF
ECHO.
ECHO I am going to delete the following files:
ECHO %1 %2
ECHO.
ECHO Press Ctrl+C to Abort process
PAUSE
FOR %%a IN (%1 %2 ) DO DEL %%a
ECHO Killed Files. Mission Accomplished.
At execution time, the process would be something like:
C:\WINDOWS>batchfilename *.tmp *.bak
I am going to delete the following files:
*.tmp *.bak
Press Ctrl+C to Abort process
Press any key to continue . . .
Killed Files. Mission Accomplished.

HACKING TRUTH

Say you want to execute a batch file and once the
procedure of
execution is complete, want to leave DOS and return to Windows, what
do you do? The EXIT command can be used in such situations. So simply end your
batch file
with the EXIT. 

Parameters: Giving Information to Batch Programs

To make batch programs really intelligent you need to be able to provide
them
with parameters which are nothing but additional valuable information
which is
needed to ensure that the bath program can work efficiently and
flexibly.
To understand how parameters work, look at the following script:
@ECHO OFF
ECHO First Parameter is %1
ECHO Second Parameter is %2
ECHO Third Parameter is %3
The script seems to be echoing(printing) messages on the screen, but
what do the
strange symbols %1 , % 2 etc stand for? To find out what the strange
symbols stand for save the above script and go to DOS and execute this script
by passing
the below parameters:
C:\windows>batch_file_name abc def ghi
This batch file produces the following result:
C:\windows>batch_file_name abc def ghi
First Parameter is abc
Second Parameter is def
Third Parameter is ghi
The first line in the output is produced by the code line:
ECHO First Parameter is %1
Basically what happens is that when DOS encounters the %1 symbol, it
examines
the original command used to execute the bath program and look for the
first
word (argument) after the batch filename and then assigns %1 the value
of that
word. So one can say that in the ECHO statement %1 is replaced with
the value of
the first argument. In the above example the first word after the
batch file name
is abc, therefore %1 is assigned the value of this word.
The %2 symbol too works in the similar way, the only difference being
that
instead of the first argument, DOS assigns it the value of the second
argument,
def. Now all these symbols, %1, %2 are called replaceable parameters.
Actually
what happens is that %1 is not assigned the value of the first argument,
but
in fact it is replaced by the value of the first argument.

If the batch file command has more parameters than what the batch
file is
looking for, then the extras are ignored. For example, if while executing
a batch
file program , we pass four arguments, but the batch file program
requires only
3 parameters, then the fourth parameter is ignored.
To understand the practical usage of parameters, let's take up a real
life
example. Now the following script requires the user to enter the name
of the
files to be deleted and the folder in which they are located.
@ECHO OFF
CD\
CD %1
DEL %2
This script can be called from the DOS prompt in the following way:
C:\windows>batch_file_name windows\temp *.tmp
In a single script we cannot use more that nine replaceable parameters.
This
means that a particular batch file will have replaceable parameters from
%1 to
%9.Infact there is a tenth replaceable parameter, the %0 parameter.
The %0
parameter contains the name of the batch file itself.

HACKING TRUTH

Say you have saved a batch file in the c:\name
directory. Now when
you launch command.com the default directory is c:\windows and in
order to
execute the batch file program stored in the c:\name directory you
need to
change the directory and go to c:\name.This can be very irritating and
time
consuming. It is a good practice to store all your batch programs in the
same folder. You can run a batch file stored in any folder(Say c:\name) from
anywhere(even c:\windows\history) if you include the folder in which the
batch
file is stored (c:\name)in the AUTOEXEC.BAT file, so that DOS knows
which folder
to look for the batch program.
So simply open c:\autoexec.bat in Notepad and append the Path
statement to the
following line[c:\name is the folder in which all your batch files are
stored.]:
SET PATH=C:\WINDOWS;C:\WINDOWS\COMMAND;C:\name
Autoexec.bat runs each time at startup and DOS knows each time, in
which
directory to look for the batch files.

ECHO OFF

This Batch File deletes all unwanted Temporary files from your system
Now we go to the Windows\temp directory.
Invalid directory
Deleting unwanted temporary files...
File not found
Your System is Now Clean
Hey pretty good! But it still shows the initial ECHO OFF command. You
can prevent a particular command from being shown but still be
executed by preceding the command with a @ sign. So to hide even the
ECHO OFF command, simple replace the
first line of the batch file with @ECHO OFF
You might think that to display a blank line in the output screen you can
simply type ECHO by itself, but that doesn't work. The ECHO command
return whether the ECHO is ON or OFF. Say you have started your
batch file with the command ECHO OFF and then in the later line give
the command ECHO, then it will display ' ECHO is off ' on the screen.
You can display a blank line by giving the command ECHO.(ECHO followed
by a dot)Simply leaving a blank line in the code too displays a blank line
in the output.
You can turn ON the ECHO anytime by simply giving the command ECHO
ON. After turning the echo on , if you give the command ECHO then it
will return ' ECHO is on '
The PAUSE Command: Freezing Time
Say you create a batch file which shows the Directory Listing of a
particular folder(DIR) before performing some other task. Or
sometimes before deleting all files of a folder, you need to give the
user time to react and change his mind. PAUSE, the name says it all, it
is used to time out actions of a script.
Consider the following scenario:
REM This Batch program deletes *.doc files in the current folder.
REM But it gives the user to react and abort this process.
@ECHO OFF
ECHO WARNING: Going to delete all Microsoft Word Document
ECHO Press CTRL+C to abort or simply press a key to continue.
PAUSE
DEL *.doc
Now when you execute this batch program, we get the following output:
C:\WINDOWS>a.bat
WARNING: Going to delete all Microsoft Word Document
Press CTRL+C to abort or simply press a key to continue.
Press any key to continue . . .
The batch file program actually asks the user if he wishes to continue
and gives the user the option to abort the process. Pressing CTRL+C
cancels the batch file program(CTRL+C and CTRL+Break bring about the
same results)
^C
Terminate batch job (Y/N)?y
After this you will get the DOS prompt back.
****************