This article was previously published under Q41246
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A feature new to the Microsoft MS-DOS packaged product is the ability touse environment variables in batch files.
These variables can be referenced by surrounding the variable with percentsymbols (%). This procedure is known as environment variable substitution.However, this ability is not present at the COMMAND.COM command line, onlywithin a batch file.
A batch file might have the following line:
%PATH% is an environment variable whose value is taken from thecurrent environment and appended to the new PATH definition. If thisis done at the command line by typing the following line, the PATHenvironment variable's value is not substituted, so the existing PATHwill not get appended to the new PATH ("%PATH%" would be appendedinstead).
The ability to use environment variable substitution is not restrictedto existing MS-DOS environment variable names. Any variable that isdefined in the environment can be extended using the method above.
If the variable specified by the SET command is not defined in theenvironment, the variable stays the same if used at the prompt, and isreplaced by a null expression if used in a batch file.
For example, type the following command in which XYZZY is an undefinedenvironment variable:
SET ONE=%XYZZY%;TWO SET
The commands result in the following if used at the command-lineprompt:
The commands result in the following if used in a batch file:
Microsoft MS-DOS 3.1, Microsoft MS-DOS 3.2 Standard Edition, Microsoft MS-DOS 3.21 Standard Edition, Microsoft MS-DOS 3.3 Standard Edition, Microsoft MS-DOS 3.3a, Microsoft MS-DOS 4.0 Standard Edition, Microsoft MS-DOS 4.01 Standard Edition, Microsoft MS-DOS 5.0 Standard Edition, Microsoft MS-DOS 5.0a, Microsoft MS-DOS 6.0 Standard Edition, Microsoft MS-DOS 6.2 Standard Edition, Microsoft MS-DOS 6.21 Standard Edition, Microsoft MS-DOS 6.22 Standard Edition