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.