Batch files can use environment variables, internal variables, variable functions, or user-defined functions. You can use these variables and functions to determine system status (e.g., the CPU type), resource levels (e.g., the amount of free disk space), file information (e.g., the date and time a file was last modified), and other information (e.g., the current date and time). You can also perform arithmetic operations (including date and time arithmetic), manipulate strings and substrings, extract parts of a filename, and read and write files.
To create temporary variables for use inside a batch file, use the SET command to store the information you want in an environment variable. Pick a variable name that isn't likely to be in use by some other program (for example, PATH would be a bad choice), and use the UNSET command to remove these variables from the environment at the end of your batch file. You can use SETLOCAL and ENDLOCAL to create a "local" environment so that the original environment will be restored when your batch file is finished.
Environment variables used in a batch file may contain either numbers or text. It is up to you to keep track of what's in each variable and use it appropriately; if you don't (for example, if you use %@EVAL to add a number to a text string), you'll get an error message or a meaningless return value.