Batch Files in DOS

Batch Files in DOS

What's a batch file?

A batch file is simply a text file that we can create by using unformatting text editor tools.

e.g. the EDIT command in MS-DOS.

A batch file must be named with an extension BAT.

e.g. autoexec.bat, menu. bat

A batch file is a program which contains MS-DOS commands. Each command used in the batch file must be started from a new line and written in a correct syntax. The syntax of a command is just the same as that you use it at the DOS prompt.

Batch Files in DOS   How does a batch file work?   Now, consider the following instructions md \newdir copy \dos\*.exe \newdir cd \newdir dir cd \     Executing commands at DOS prompt: Normally, we can execute only one MS-DOS command at one time (except we use a "trick"). We cannot give another instruction before DOS has done our current command.   If we manually instruct DOS to execute the above commands, we have to type each command at the DOS prompt one after another.     Executing commands in a batch file: However, if we put all of the commands in a text file in the same manner as in the above box, it becomes an executable program.   Let's name it anyname.bat Similar to a COM or EXE command, we can simply type the name of this batch file at the DOS prompt to start our instructions.   i.e. C:\>anyname or C:\>anyname.bat (note: the extension bat is optional here. It makes no difference, no matter we put it or not.)   DOS will then execute the commands automatically in the same order as written in the anyname.bat The followings are details of what DOS will do for us:- 1. Creates a new directory under the root called newdir 2. Copies all files under the DOS directory with an extension of EXE to the newly created newdir directory. 3. Changes the current directory to newdir directory 4. Display the directory listing of newdir directory 5. Changes the current directory to root directory         Batch Files in DOS   What commands can we used in a batch file?   All commands that we can use at the DOS prompt can be used in a batch file. We have to follow the same syntax of the commands as we use it at the DOS prompt.   For advanced application of batch programs, the following nine (9) special commands are commonly used. Some of them are used together with special characters.   CALL FOR PAUSE CHOICE * GOTO REM ECHO IF SHIFT CHOICE is an external DOS command.   Note:- Please ensure the current path statement contains C:\DOS when we need to run a batch program in which the CHOICE command is used.   Brief Description of MS-DOS Batch Commands CALL Calls one batch program from another.   CHOICE Waits for the user to choose one of a set of choices.   ECHO Displays messages, or turns command-echoing on or off.   FOR Runs a specified command for each file in a set of files.   GOTO Directs MS-DOS to a labelled line in a batch program.   IF Performs conditional processing in batch programs.   PAUSE Suspends processing of a batch program and displays the message "Press any key to continue...."   REM comments (remarks) in a batch file or CONFIG.SYS.   SHIFT Changes the position of replaceable parameters in a batch file.         Batch Files in DOS   What are the special characters commonly used in a batch file?     Batch display-suppression operator o @ can be applied to any command as the first character on the command line in a batch program. o It's used to prevent an individual command from being displayed when it is executed.     Batch file label operator o : is used to identify a location in a batch file. It is not a command but a prefix of a label.   o A label is a companion of the GOTO command. i.e. GOTO <label> :<label>   o A label is used to force MS-DOS to move to a specified location within the batch program.   o Normally, when MS-DOS runs a batch program, it executes commands in the order as they appear in the program. However, when MS-DOS comes across the GOTO command(e.g. GOTO option1), it will move to the position that is identified by :option1 within the batch program.     Batch replaceable parameter o Consider the following commands frequently used at the DOS prompt:-   ? copy autoexec.bat autoexec.bak This command line creates a backup file of the autoexec.bat file. copy is a command, autoexec.bat and autoexec.bak are parameters. These are required parameters. You must state both of them to make the command work.     ? dir /w This command line displays a directory entries of the current directory in wide screen format. dir is a command, /w is a parameter. It is an optional parameter for qualifying the output of the dir command.   o Similarly, we can make use of parameters to help us achieve the same capability in executing a batch program. This way, we can execute the same batch program with different data at different time. They are called replaceable parameters.   o %n and %%n are the special characters which represent the parameter in a batch program, where n is a single digit, from 1 through 9.   o The replaceable parameters are positional. The digit, n, of the special characters represents the position of the parameter we type with the batch command.   For example:         Batch Files in DOS   How can we create a batch file?   • EDIT command o Usage: EDIT filename.bat Where filename.bat is an optional parameter. We are recommended to give a name when we open the editor because it will simplify some steps in saving the file when it's done.   o Run EDIT command at the command prompt, we will go to an editor mode, normally in blue screen. Make sure we have saved the file upon completion.   o Remember to give an extension of .BAT in your batch file.     • COPY command o Usage: COPY con filename.bat Where filename.bat is a required parameter if we want to save the file. We must give a name when we run COPY command.   This method is useful when you are writing a short batch file. o "COPY con filename" 1. Similar to backup a file using COPY command, "COPY con filename" means copying from "con" (the source) to a file called filename.bat (the target).   2. CON is a reserved name for console. The keyboard is known to MS-DOS as console.   3. By running the command, we instruct MS-DOS to copy what we type from the keyboard to a file filename.bat . When MS-DOS display a blinking cursor instead of a command prompt, it means it's ready for we to type in any text.   4. Remember to use Ctrl-Z (i.e. hold down the ctrl key and hit Z) or press the function key F6 to end the file. MS-DOS will display ^Z on the screen. It is the end of file marker.   5. And then, press Enter to save the file. MS-DOS will signal back "1 file(s) copied" and return to the command prompt.     • DOSKEY command o Usage: DOSKEY /h > filename.bat   o This method is useful for a "write-and-test" approach. While we are writing a batch file, we are working on the command prompt directly. By the way, we can know the result of every command immediately.   o The DOSKEY program, once loaded into memory, keeps track of the commands we have typed through the keyboard.   o DOSKEY /h -- displays all commands stored in memory.   o By running the command, we instruct MS-DOS to redirect the history of commands to a batch file filename.bat .   o Steps in using this method: 1. Make sure DOSKEY program has been loaded into memory.   2. Press Alt-F7 to clear the memory buffer before we "write-and-test" our file.   3. Run the commands that we want to put in the batch file.   4. Upon completion, run DOSKEY /h > filename.bat   5. Run EDIT filename.bat to delete the last line "i.e. DOSKEY /h > filename.bat" and all other unnecessary lines, if necessary.