Command-Line Length Limits

When you first enter a command at the prompt or in an alias or batch file, 
it can be up to 1,023 characters long. 

As CMD.EXE scans the command line and substitutes the contents of aliases 
and environment variables for their names, the line usually gets longer. 
 This expanded line is stored in an internal buffer which allows each 
individual command to grow to 1,023 characters during the expansion 
process.  In addition, if you have multiple commands on a single line, 
during expansion the entire line can grow to as much as 2,047 characters. 
 If your use of aliases or environment variables causes the command line 
to exceed either of these limits as it is expanded, you will see a 
"Command line too long" error and the remainder of the line will not be 
executed.