Q41246: How to Use Environment Variable Substitution in Batch Files

Article: Q41246
Product(s): Microsoft Disk Operating System
Version(s): MS-DOS:3.x,4.x,5.x,6.0,6.2,6.21,6.22
Operating System(s): 
Keyword(s): 
Last Modified: 17-DEC-2000

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The information in this article applies to:

- Microsoft MS-DOS operating system versions 3.1, 3.2, 3.21, 3.3, 3.3a, 4.0, 4.01, 5.0, 5.0a, 6.0, 6.2, 6.21, 6.22 
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SUMMARY
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A feature new to the Microsoft MS-DOS packaged product is the ability to use
environment variables in batch files.

These variables can be referenced by surrounding the variable with percent
symbols (%). This procedure is known as environment variable substitution.
However, this ability is not present at the COMMAND.COM command line, only
within a batch file.

MORE INFORMATION
================

A batch file might have the following line:

  SET PATH=c:\dos\bin;c:\dos\etc;%PATH%.

%PATH% is an environment variable whose value is taken from the current
environment and appended to the new PATH definition. If this is done at the
command line by typing the following line, the PATH environment variable's value
is not substituted, so the existing PATH will not get appended to the new PATH
("%PATH%" would be appended instead).

   SET PATH=c:\dos\binp;c:\os2\binp;%PATH%

The ability to use environment variable substitution is not restricted to
existing MS-DOS environment variable names. Any variable that is defined in the
environment can be extended using the method above.

If the variable specified by the SET command is not defined in the environment,
the variable stays the same if used at the prompt, and is replaced by a null
expression if used in a batch file.

For example, type the following command in which XYZZY is an undefined
environment variable:

  " SET ONE=%XYZZY%;TWO
  SET" (without the quotation marks)

The commands result in the following if used at the command-line prompt:

  one=%XYZZY%;TWO

The commands result in the following if used in a batch file:

  ONE=;TWO

Additional query words: 6.22 3.30 3.30a 4.00 4.01 5.00 5.00a 6.00 6.20

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Keywords          :  
Technology        : kbMSDOSSearch kbMSDOS321 kbMSDOS400 kbMSDOS320 kbMSDOS330a kbMSDOS621 kbMSDOS622 kbMSDOS620 kbMSDOS600 kbMSDOS310 kbMSDOS500 kbMSDOS330 kbMSDOS401 kbMSDOS500a
Version           : MS-DOS:3.x,4.x,5.x,6.0,6.2,6.21,6.22

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