How To Using IF Command Syntax For Batch Files

The IF command in batch scripting is very similar to the IF statement in other programming languages. The IF command allows you to take a batch file in one of two ways. The basic scheme of a batch file is:

IF command syntax:

• IF {Statement} {If statement is TRUE, perform this action}

If the statement being tested is TRUE perform the action on that line. If the statement is FALSE continue to the next line. The TRUE action statement is then, essentially, ignored. A GOTO statement could perhaps be present on this line to send processing of the batch file to another location in the script. The IF command is great for testing three types of conditions including replaceable parameters, system ERRORLEVEL, and it can compare two strings.

Remember that several IF commands can be issued to overcome a more complex problem and create a more detailed algorithm. An algorithm is simply your solution to the problem at hand.

Here is an example that tests replaceable parameters (Note that on some versions of Windows or a different configuration of your command prompt might change how this example is run. Play around with it and your DOS settings.):

:: LOOP.BAT
:: Compares Replaceable parameters.
@ECHO OFF
:TOP
   IF (%1)==() GOTO END
   ECHO Value is "%1" and still running...
   SHIFT
GOTO TOP
:END

The first two lines are remark statements indicating the name of the program as well as a brief description of what the program does. The third line brings command echoing to a standstill. Line four marks off the sub program that a GOTO command could hop to. Line 5 tests for a blank replaceable parameter. When %1 contains any information then that information gets placed in the first set of parentheses (parameter)==() and evaluates to FALSE. This is what we want. A common mistake is to omit the parentheses, however we need them so we do not create an infinite loop.

When replaceable parameter %1 is empty, the test becomes ()==() and appropriately evaluates to TRUE. This line is the core code of this program. When the expression evaluates to TRUE the GOTO END command is implemented. This ends the program. When the expression (condition) is FALSE, the next line of code is executed. The sixth line displays the value of parameter combined in message, Value is "something" and still running... using the ECHO command. That next line of code contains the SHIFT command. We know that the SHIFT command shifts the values of replaceable parameters over. The last line is the END sub-program that has nothing contained within signifying the end of the program.

Note that the indents do not change your code and are not necessary. It is easier to read this if we indent everything inside of the :TOP sub-program as shown.

The IF command is a great command by itself however it yields great possibilities when combined with other commands. Such as the EXIST command. The EXIST command is used to test the existence of a file. This can be done using the following syntax scheme:

IF EXIST command syntax:

• IF EXIST {filename} {If filename exist, perform this action}

In order for this command to work you are to place the file name where the filename in its respective location as shown above followed by the action to take. An example showing a possible use:

:: ExistFile.BAT
:: Example of IF EXIST command sequence.
@ECHO OFF
IF EXIST %1 ECHO File %1 exists!
IF EXIST %2 ECHO File %2 exists!
IF EXIST %3 ECHO File %3 exists!

Lines 1 and 2 are remark statements indicating the name of the batch file and a brief description of what the batch file does. Line 3 turns off command echoing. Lines 4 through line 6 tests the existence of whatever values are in the replaceable parameters 1, 2, and 3 respectively. This program is rather trivial in that in its current state there are no actual contents filling each replaceable parameter.