Lably
Skip to content

Batch file

Script file for Microsoft computer operating systems

  • 18 min read
  • 7 chapters

Related on Lably

Through DOS, Microsoft Windows and Command (computing)

Similar to Job Control Language (JCL), DCL and other systems on mainframe and minicomputer systems, batch files were added to ease the work required for certain regular tasks by allowing the user to set up a script to automate them. When a batch file is run, the shell program (usually COMMAND.COM or cmd.exe) reads the file and executes its commands, normally line-by-line. Unix-like operating systems, such as Linux, have a similar, but more flexible, type of file called a shell script.

The filename extension .bat is used in DOS and Windows. Windows NT and OS/2 also added .cmd. Batch files for other environments may have different extensions, e.g., .btm in 4DOS, 4OS2 and 4NT related shells.

The detailed handling of batch files has changed significantly between versions. Some of the detail in this article applies to all batch files, while other details apply only to certain versions.

Variants

DOS

In MS-DOS, a batch file can be started from the command-line interface by typing its name, followed by any required parameters and pressing the ↵ Enter key. When DOS loads, the file AUTOEXEC.BAT, when present, is automatically executed, so any commands that need to be run to set up the DOS environment may be placed in this file. Computer users would have the AUTOEXEC.BAT file set up the system date and time, initialize the DOS environment, load any resident programs or device drivers, or initialize network connections and assignments.

A .bat file name extension identifies a file containing commands that are executed by the command interpreter COMMAND.COM line by line, as if it were a list of commands entered manually, with some extra batch-file-specific commands for basic programming functionality, including a GOTO command for changing flow of line execution.

Early Windows

Microsoft Windows was introduced in 1985 as a graphical user interface-based (GUI) overlay on text-based operating systems and was designed to run on DOS. In order to start it, the WIN command was used, which could be added to the end of the AUTOEXEC.BAT file to allow automatic loading of Windows. In the earlier versions, one could run a .bat type file from Windows in the MS-DOS Prompt. Windows 3.1x and earlier, as well as Windows 9x invoked COMMAND.COM to run batch files.

OS/2

The IBM OS/2 operating system supported DOS-style batch files. It also included a version of REXX, a more advanced batch-file scripting language. IBM and Microsoft started developing this system, but during the construction of it broke up after a dispute; as a result of this, IBM referred to their DOS-like console shell without mention of Microsoft, naming it just DOS, although this seemingly made no difference with regard to the way batch files worked from COMMAND.COM.

OS/2's batch file interpreter also supports an EXTPROC command. This passes the batch file to the program named on the EXTPROC file as a data file. The named program can be a script file; this is similar to the #! mechanism used by Unix-like operating systems.

Windows NT

Unlike Windows 98 and earlier, the Windows NT family of operating systems does not depend on MS-DOS. Windows NT introduced an enhanced 32-bit command interpreter (cmd.exe) that could execute scripts with either the .CMD or .BAT extension. Cmd.exe added additional commands, and implemented existing ones in a slightly different way, so that the same batch file (with different extension) might work differently with cmd.exe and COMMAND.COM. In most cases, operation is identical if the few unsupported commands are not used. Cmd.exe's extensions to COMMAND.COM can be disabled for compatibility.

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.

Sign in to keep reading

6 more chapters are free with a Lably account.

More in Computing and communication