Batch file set variable to null

Privacy policy. Displays, sets, or removes cmd. If used without parameters, set displays the current environment variable settings. The set command can also run from the Windows Recovery Console, using different parameters.

If command extensions are enabled the default and you run set with a value, it displays all of the variables that begin with that value. If you use quotation marks to enclose a string that contains one of the special characters, the quotation marks are set as part of the environment variable value.

Use environment variables to control the behavior of some batch files and programs and to control the way Windows and the MS-DOS subsystem appears and works. The set command is often used in the Autoexec. If you use the set command without any parameters, the current environment settings are displayed. The "script" in this context being a line - or block - of code, surrounded by round brackets:. In the above example, the ECHO command is evaluated as Hello when the script is read into memory, so the script will echo Hello forever, however many passes are made through the script.

The way to achieve the more "traditional" variable behaviour of the variable being expanded whilst the script is running is to enable "delayed expansion". This involves adding that command into the script prior to the loop instruction usually a FOR loop, in a batch script , and using an exclamation mark!

Now, an advanced technique. Using the CALL command allows the batch command processor to expand a variable located on the same line of the script. This can deliver multilevel expansion, by repeated CALL and modifier use. This is useful in, for example, a FOR loop. As in the following example, where we have a numbered list of variables:.

Note that the variable! This is double expansion of the variable i. Thus it increases to 2 on the 2nd pass through the loop, and to 3 on the 3rd pass. If you have variables that would be used across batch files, then it is always preferable to use environment variables. Following is an example of an output. Batch Script - Variables Advertisements.

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