Long Command Lines

Although in previous versions of MS-DOS the limit for environment variables and batch file lines is 128 characters, it is 1024 characters in Windows 95/98. The limit for the keyboard buffer, however, is still 128 characters. Although 1024 and 128 are the standard limits, users may configure their systems to lower these limits.

In previous versions of MS-DOS, command-line arguments are located in the command tail of the program segment prefix (PSP). The command tail in the PSP is limited to 128 characters, including the leading byte that specifies the length of the command line and the trailing carriage return character. In Windows 95/98, if the command line is less than or equal to 126 characters, it is set in the command tail of the PSP. For command lines that are greater than 126 characters, an application should follow these steps:

1. Set the count byte in the command tail to 7Fh.
2. Fill in 7Eh bytes of the command tail followed by the carriage return character (0Dh).
3. Place the rest of the command line in the CMDLINE environment variable.