If Command Extensions are enabled SET changes as follows: SET command invoked with just a variable name, no equal sign or ...

If Command Extensions are enabled SET changes as follows:    SET command invoked with just a variable name, no equal sign or value  will display the value of all variables whose prefix matches the name  given to the SET command.  For example:        SET P    would display all variables that begin with the letter 'P'    SET command will set the ERRORLEVEL to 1 if the variable name is not  found in the current environment.    SET command will not allow an equal sign to be part of the name of  a variable.    Two new switches have been added to the SET command:        SET /A expression      SET /P variable=[promptString]    The /A switch specifies that the string to the right of the equal sign  is a numerical expression that is evaluated.  The expression evaluator  is pretty simple and supports the following operations, in decreasing  order of precedence:        ()                  - grouping      ! ~ -               - unary operators      * / %%               - arithmetic operators      + -                 - arithmetic operators      << >>               - logical shift                         - bitwise and      ^                   - bitwise exclusive or      |                   - bitwise or      = *= /= %%= += -=    - assignment        &&= ^= |= <<= >>=      ,                   - expression separator    If you use any of the logical or modulus operators, you will need to  enclose the expression string in quotes.  Any non-numeric strings in the  expression are treated as environment variable names whose values are  converted to numbers before using them.  If an environment variable name  is specified but is not defined in the current environment, then a value  of zero is used.  This allows you to do arithmetic with environment  variable values without having to type all those %% signs to get their  values.  If SET /A is executed from the command line outside of a  command script, then it displays the final value of the expression.  The  assignment operator requires an environment variable name to the left of  the assignment operator.  Numeric values are decimal numbers, unless  prefixed by 0x for hexadecimal numbers, and 0 for octal numbers.  So 0x12 is the same as 18 is the same as 022. Please note that the octal  notation can be confusing: 08 and 09 are not valid numbers because 8 and  9 are not valid octal digits.