Batch Script Variables

Types of Variables

There are two types of variables in batch files. One is for parameters that can be passed when the batch file is called, and the other is done through the set command.

Command Line Arguments

Batch scripts support the concept of command-line arguments, in which arguments can be passed to the batch file when it is invoked.

The arguments can be called from the batch files through the variables %1, %2, %3, and so on.

For example, the batch script below accepts 3 command line arguments and echo’s them to the command line screen:

parameter-test.bat

@echo off
echo %1
echo %2
echo %3

If the above batch script is stored in a file called parameter-test.bat and we were to run the batch as:

C:\my\path>parameter-test.bat 1 2 3

And the above command produces the following output:

1
2
3

note

If more parameters are passed than are used, the extra ones will be ignored.

For example, here the fourth parameter is ignored but the output remains the same as above:

C:\my\path>parameter-test.bat 1 2 3 4

set Command

The other way to initialize variables is the set command. The syntax of the set command is as follows.

set /A variable_name=value

where:

• variable_name is the name of the variable you want to set.
• value is the value which needs to be set against the variable.
• /A is used if the value needs to be numeric.

For example, in this script a variable called message is defined and set with the value of "Hello World".

set-example.bat

@echo off
set message=Hello World
echo %message%

note

To display the value of the variable, the variable needs to be enclosed in the % sign.

And the above command produces the following output:

Hello World

Numeric Variables

It is possible to define a variable to hold a numeric value. This can be done by using the /A switch (also known as flag).

For example:

numeric-example.bat

@echo off
SET /A a = 5
SET /A b = 10
SET /A c = %a% + %b%
echo %c%

where:

• we assign the values 5 and 10 to two variables a and b respectively.
• we sum these values and store the result in the variable c.
• Finally, we display the value of the variable c.

The output of the above script is 15.

Arithmetic Operators

All the arithmetic operators work in batch files.

For example:

arithmetic-example.bat

@echo off
SET /A a = 5
SET /A b = 10
SET /A c = %a% + %b%
echo %c%
SET /A c = %a% - %b%
echo %c%
SET /A c = %b% / %a%
echo %c%
SET /A c = %b% * %a%
echo %c%

And the output is:

15
-5
2
50

note

You can learn more about operators in our Batch Script Operators Chapter

Local and Global Variables

In Batch Scripting there are variables with local and global scope.

By default, variables are global to your entire command prompt session.

Call the SETLOCAL command to make variables local to the scope of the script. After calling SETLOCAL, any variable assignment is cancelled when ENDLOCAL, EXIT or when execution reaches the end of file (EOF) in the script is called.

The difference between setting local and global variables is shown in the following script:

@echo off
set globalvar = 5
SETLOCAL
set var = 13145
set /A var = %var% + 5
echo %var%
echo %globalvar%
ENDLOCAL

note

• The globalvar is defined with a global scope and it is available throughout the entire script.
• The variable var is defined in a local scope because it is enclosed between a SETLOCAL and ENDLOCAL block. Therefore, this variable will be destroyed as soon as the ENDLOCAL instruction is executed.

Environment Variables

Environment Variables are preferable when there are variables that would be used across batch files.

note

Once the environment variable is defined, it can be accessed via the % sign (like any variable).

The following example shows how to see the JAVA_HOME defined on a system.

@echo off 
echo %JAVA_HOME%

C:\mypath\JAVA5.0\jre

note

The JAVA_HOME variable is a key component that is normally used by a wide variety of Java-based applications.