Batch File Programming Part-4

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.

In the next post we will see some more concepts of Batch File Programming.