SET

Displays, sets, or removes environment variables (of CMD.EXE).

SET [variable[=[value]]]

SET [letter]

SET [/A [variable=]"expression"]

SET [/P variable=[promptstring]]

Where:

variable - Specifies the environment variable to give a value to (defines the specified variable). If neither = nor value is specified, it will display the value of the environment variable (if defined). If = is specified but not value, it will remove the specified environment variable (if defined).
value - Specifies the value to give to the variable specified by defining it (the value is a word, phrase, number, or other).
letter - Displays the value of environment variables whose names begin with the specified letters.
/A - Specifies that an arithmetic expression must be calculated. If variable is specified, the specified environment variable will be defined with the result of the expression.
"expression" - Specifies the expression whose result will be displayed. If variable is specified, the specified environment variable will be defined with the result of the expression.
/P - Specifies that the environment variable must be user-defined (i.e., anyone opening the batch file containing this command will have the option to write any string).
promptstring - Displays the specified character string which can be a question or a request.

What is the purpose of defining variables?

As explained above, enclosing the environment variable in percentage symbols % % will expand its value (if defined, of course).

The following operators can be used in arithmetic expressions:

( ) - Grouping (brackets).
! ~ - Logical and bitwise NOT operators (respectively).
+ - Plus symbol (arithmetic addition).
- - Minus symbol (arithmetic subtraction).
* - Times symbol (arithmetic multiplication).
/ - Divided-by symbol (arithmetic division).
<< >> - Bitwise shift.
& - Bitwise AND.
^ - Bitwise XOR (exclusive or).
| - Bitwise OR.
c=n - Assignment (where c is any character other than a number or symbol among those specified and n is a number or expression).
, - Expression separator (NB: if this character is specified one or more times, the last result will be used to set the environment variable).

Note that if no arguments are added to the SET command, the complete list of defined environment variables will be displayed.

Examples:

1. Assign the FOO value to the hugh environment variable:

set hugh=FOO

2. Assign the value of the expression 15+18 (33) to the environment variable HOWMUCH:

set /a HOWMUCH="15+18"

3. Return the value of the user's response to the CHOICE environment variable by displaying Hi Foo, what is 1+1? (see Batch files Batch files):

set /p CHOICE=Hi Foo, what is 1+1?

Further information:

To expand an environment variable you need to put it between percentages % %, for example %CHOICE%, but for custom expansions there are different syntaxes:

%CHOICE:word1=word2%

This line expands the CHOICE environment variable by replacing the words word1 with the words word2. word2 may be left unspecified to remove the words word1.

%CHOICE:~2,4%

Expands the first 4 characters starting from the third character (skipping the first 2 characters) of the CHOICE environment variable. If 4 is not specified, it extracts the first 2 characters of the CHOICE environment variable. If 0 is specified in the first number, it extracts all characters except the first 4.

%CHOICE:~-4%

Expands the last 4 characters of the CHOICE environment variable.

%CHOICE:~0,-4%

Expands all characters except the last 4 of the CHOICE environment variable.

by Alessandro

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