Environment Variables and Functions

The environment is a collection of information about your computer that 
every program receives.  Each entry in the environment consists of a 
variable name, followed by an equal sign and a string of text.  You can 
automatically substitute the text for the variable name in any command. 
 To create the substitution, include a percent sign [%] and a variable 
name on the command line or in an alias or batch file. 

The following environment variables have special meanings in CMD.EXE: 

            CDPATH 
            CMDLINE 
            COLORDIR 
            COMSPEC 
            FILECOMPLETION 
            PATH 
            PATHEXT 
            PROMPT 
 
 CMD.EXE also supports two special types of variables.  Internal variables 
 are similar to environment variables, but are stored internally within 
 CMD.EXE, and are not visible in the environment.  They provide 
 information about your system for use in batch files and aliases. 
  Variable functions are referenced like environment variables, but 
 perform additional functions like file handling, string manipulation and 
 arithmetic calculations. 

 In CMD.EXE the size of the environment is set automatically, and 
 increased as needed when you add variables. 

 The SET command is used to create environment variables. For example, you 
 can create a variable named BACKUP like this: 

 
         [c:\] set BACKUP=*.bak;*.bk!;*.bk
 

 If you then type 

 
         [c:\] del %BACKUP
 

 it is equivalent to the following command: 

 
         del *.bak;*.bk!;*.bk
 

 Environment variable names may contain any alphabetic or numeric 
 characters, the underscore character [_], and the dollar sign [$].  You 
 can force acceptance of other characters by including the full variable 
 name in square brackets, like this: %[AB##2].  You can also "nest" 
 environment variables using square brackets.  For example %[%var1] means 
 "the contents of the variable whose name is stored in VAR1".  A variable 
 referenced with this technique cannot contain more than 255 characters of 
 information.  Nested variable expansion can be disabled with the SETDOS 
 /X command. 

 Environment variables may contain alias names.  The command processor 
 will substitute the variable value for the name, then check for any alias 
 name which may have been included within the variable's value.  For 
 example, the following commands would generate a 2-column directory of 
 the .TXT files: 

 
         [c:\] alias d2 dir /2
         [c:\] set cmd=d2
         [c:\] %cmd *.txt
 

 The trailing percent sign that was traditionally required for environment 
 variable names is not usually required in CMD.EXE, which accept any 
 character that cannot be part of a variable name (including a space) as 
 the terminator.  However, the trailing percent can be used to maintain 
 compatibility. 

 The trailing percent sign is needed if you want to join two variable 
 values.  The following examples show the possible interactions between 
 variables and literal strings.  First, create two environment variables 
 called ONE and TWO this way: 

 
         [c:\] set ONE=abcd
         [c:\] set TWO=efgh
 

 Now the following combinations produce the output text shown: 

 
         %ONE%TWO            abcdTWO   ("%ONE%" + "TWO")
         %ONE%TWO%           abcdTWO   ("%ONE%" + "TWO%")
         %ONE%%TWO           abcdefgh  ("%ONE%" + "%TWO")
         %ONE%%TWO%          abcdefgh  ("%ONE%" + "%TWO%")
         %ONE%[TWO]          abcd[TWO] ("%ONE%" + "[TWO]")
         %ONE%[TWO]%         abcd[TWO] ("%ONE%" + "[TWO]%")
         %[ONE]%TWO          abcdefgh  ("%[ONE]" + "%TWO")
         %[ONE]%TWO%         abcdefgh  ("%[ONE]" + "%TWO%")
 

 If you want to pass a percent sign to a command, or a string which 
 includes a percent sign, you must use two percent signs in a row. 
 Otherwise, the single percent sign will be seen as the beginning of a 
 variable name and will not be passed on to the command.  For example, to 
 display the string "We're with you 100%" you would use the command: 

 
         echo We're with you 100%%
 

 You can also use back quotes around the text, rather than a double 
 percent sign.  See Argument Quoting for details.