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IF Exist - Testing: Use the zero-byte (zero length) file as an "exit" ramp or for a "goto" statement within a batch-file or script. It provides a directory listing, but requires no disk space. IF EXIST C:\NOTHING.TXT EXIT IF NOT EXIST C:\NOTHING.TXT GOTO START : START REM Create the zero-length file C : \ >type null>nothing.txt : EXIT
If rd/rmdir gets executed without regard to case sensitivity and Windows chooses the legitimate folder to delete, the only folder left is the undesired one. Windows then uses this folder instead of the previously legitimate one to execute programs, and one may be led to believe it contains legitimate data.
The Call command in COMMAND.COM only supports calling external batch files. File name parser extensions to the Set command are comparable with C shell. [further explanation needed] The Set command can perform expression evaluation. An expansion of the For command supports parsing files and arbitrary sets in addition to file names.
IF is a conditional statement, that allows branching of the program execution. It evaluates the specified condition, and only if it is true, then it executes the remainder of the command line. Otherwise, it skips the remainder of the line and continues with next command line. Used in Batch files. The command is available in MS-DOS versions 2 ...
COMMAND.COM is the default command-line interpreter for MS-DOS, Windows 95, Windows 98 and Windows Me.In the case of DOS, it is the default user interface as well. [2] It has an additional role as the usual first program run after boot (init process), hence being responsible for setting up the system by running the AUTOEXEC.BAT configuration file, and being the ancestor of all processes.
Microsoft released a version of cmd.exe for Windows 9x and ME called WIN95CMD to allow users of older versions of Windows to use certain cmd.exe-style batch files. As of Windows 8, cmd.exe is the normal command interpreter for batch files; the older COMMAND.COM can be run as well in 32-bit versions of Windows able to run 16-bit programs.
Similarly, changing or removing a variable's value inside a DOS or Windows batch file will change the variable for the duration of COMMAND.COMor CMD.EXE's existence, respectively. In Unix, the environment variables are normally initialized during system startup by the system init startup scripts , and hence inherited by all other processes in ...
One can use these mechanisms to write specific command processors for dedicated uses, and process external data files which reside in batch files. Many graphical interfaces, such as the OS/2 Presentation Manager and early versions of Microsoft Windows use command lines to call helper programs to open documents and programs.