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1- What is a variable?
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Variable is a basic concept in computer science. It is a value that can change. Like other languages,
Batch also has the concept of variable.
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Basically,
Batch has 2 kinds of variables:
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- Variables are declared in a file through the set command.
- Argument variables are passed from outside when the file is called for execution.
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2- Common variables
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Batch language does not have a clear concept of data type. Normally, a variable has the value that is a string, including characters after the
= sign to the end of the line. (Including whilte spaces if applicable).
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In case you want to declare a variable which is a number, you need to use the
set /A statement
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To access value of a variable, you must enclose it in % signs.
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Example:
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variableExample1.bat
@echo off
set name=Tran
set /A age= 37
echo %name%
echo %age%
set info=My Name is: %name%, Age: %age%
echo %info%
pause
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variableExample2.bat
@echo off
set /A a = 100
set /A b = 200
echo a = %a%
echo b = %b%
set /A sum = a + b
echo Sum = %sum%
pause
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3- Argument variables
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When calling to execute a
batch file, you can pass values to the file. You can access these values through the variables such as
%1,
%2,
%3,... in the file. These variables are also called argument variables.
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argumentVariables.bat
@echo off
@echo First argument is: %1
@echo Second argument is: %2
pause
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We test the above example by opening the
CMD window and
CD to go to the folder containing the
argumentVariables.bat file
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Execute the
argumentVariables.bat file with parameters.
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Results:
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4- Scope of variable
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When a Command Window is opened, it will start a session. Such session will finish upon closing the Command Window. During a session you can execute one or more
batch files. The variables created in the previous file can be visited in the following file. Such variables are called global variables. However, you can create a local variable. The local variable only exists within the file of defining it or in a section of that file.
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Example of Local Variables
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Local variables are declared in a block, starting with
setlocal and ending with
endlocal.
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localVariable.bat
@echo off
set global1=I am a global variable 1
setlocal
set local1=I am a local variable 1
set local2=I am a local variable 2
echo ----- In Local Block! -----
echo local1= %local1%
echo local2= %local2%
endlocal
echo ..
echo ----- Out of Local Block! -----
echo global1= %global1%
echo local1= %local1%
echo local2= %local2%
pause
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Example of Global Variables:
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Variables, declared in the
Batch file, and not located in the
setlocal .. endlocal block, will be global variables. They can be used in other files in the same session.
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In this example, we have two files such as
batchFile1.bat and
batchFile2.bat. The
MY_ENVIRONMENT variable is defined in file 1, and which is used in file 2.
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batchFile1.bat
@echo off
set MY_ENVIRONMENT=C:/Programs/Abc;C:/Test/Abc
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batchFile2.bat
@echo off
echo In batchFile2.bat
echo MY_ENVIRONMENT=%MY_ENVIRONMENT%
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Open CMD, and CD to the folder containing the
batchFile1.bat,
batchFile2.bat files and run these files respectively.
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5- The environment variables of Windows
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Windows allow you to create
environment variables. These variables will be global variables which can be used in any
batch file.
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On the
Windows, select:
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- Start Menu/Control Panel/System
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- Advanced (Tab) > Environment Variables..
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Here, you can create an environment variable for current
user, or a system environment variable that can be used by any user.
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For example, I create a environment variable with the name of
MY_ENVIRONMENT_VARIABLE and its value of
"My Environment Variable Value!".
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And you can use the environment variable created in a
batch file.
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testEnvVariable.bat
@echo off
echo %MY_ENVIRONMENT_VARIABLE%
pause
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