In DOS, there are several types of commands. They are internal and external commands. Internal commands have not varied much since DOS 2X. External ones have. We can see the evolution of commands by their extensions and scope. External commands tend to be more powerful than internal commands but at a cost of being stored on disk.
Internal commands are DOS commands embedded into cmd.exe shell. They are always available to the user and tend to focus on file and folder commands. An example of a internal command would be “CLS” to clear the screen.
External commands are not located in the shell but are in program files stored on disk. They are a combination of .exe and .com files mostly found in the \windows\system32 folder. An example of a external command would be “MORE.COM” to pause the output of a command. .com files are limited to 64K memory mapping. .exe files are more extensive and can also include header information and icons too. Most executable files today are .exe files. (See links for more detailed information on these file types.)
DOS commands for which the specifications are available in Shell (Command.com) are calledinternal commands. These are frequently used commands, and are called resident commands.
DOS Commands for which specifications are not internally available in command.com are called External Commands. They reside in the disk in the form of executable program files. They will be loaded into primary memory only at the time of execution.
Directory Structure of DOS: One thing is to be kept in mind is that a directory can have as many child (sub) directories, but the child directory can have only one parent directory.
1. CLS: this command is used to clean the screen.
2. DIR: this command allows the user to see all files and sub-directory in the current directory. DIR Command lists file information in five columns; (first) column gives primary name of the file (second) column gives extension of the file (third) column gives the file size – number of bytes used; (fourth) column gives the last updated date; (fifth) column gives the last updated time.
Dir/p – page by page display of file name and directory names;
Dir/w – width-wise display;
Dir/s – displays all sub directory and files in the sub-directory of current directory.
3. Copy con this command copies whatever typed on keyboard to the file; the file can be closed by giving the command A2 or F6 key: eg: Copy con test …..A2.
4. Date it displays two system date and allows the user to change it if desired ; it is displayed in the form of mm – dd – yy; eg:c:\> date – enter.
5. Time it displays the system type and enables the user to change it; eg: C:\> Time – enter.
6. md(mkdir) it creates a new directory in sub directory in the current directory; eg: C:\> md <New directory name>
7. rd(rmdir) this command is used to remove a directory from the disk; it can’t remove a directory which contains sub directory or files, ie, the child should be removed from the parent; similarly this command can’t remove the current directory and root directory. Syntax: c:\> RD<Dir name>.
8. Type it displays the content of saved file; eg: C:\> Type> file name.
9. Ren this command changes the name of existing file or directory: Syntax: C:\> ren <old name> new name>
10. Delete delete a file from current directory; Syntax: C;\> del<file name>
11. Ver it displays the version of DOS currently being used in the system; Syntax: C:> ver
12. Copy it copies the given file or files from the source directory to the largest directory; Syntax:C:\> copy<source file name> <target file name>.
13. Prompt allows the user to set a new DOS prompt instead of usual C:\> or A:\>; eg C:\> prompt pcc; Prompt$p$g – this allows you to reset default prompt; Prompt $d (current date); Prompt $t (current time);
1. Attrib this command is used for protecting the files from accidental changes or modification. It can also be used for making a hidden file, archive files, read only files; Syntax: Attrib +R/-R/+H/-H/+A/-A <file name> +FR protects the file by making it read only, -R removes the read only protection; eg: Attrib + r <file name >
2. Scandisk/ Chkdisk this command checks the status of the disk; it shows a graphical display, information about the user file.
3. Tree this command graphically displays the path of each directory and sub directory in given drive; Syntax: C:\> tree<
4. More it displays one screen of data at a time and is used with another command when one screen is full; if you press any key on the next screen is displayed: Syntax C:\> type abc.doc| more.
5. Edit the command loads the MSDOS editor, where we can edit files, create new files, open existing files; Syntax: C:\> edit < file name>
6. Label a label is a name given to a disk which refers to collection of filers and directories on disk; Syntax: C:\>label A.
7. Sort this command is used for sorting data and displaying the result on the screen: Syntax:C:\>dir/sort/r (reverse order)
8. Format; this command prepares a disk by arranging random magnetic impulses in to a series of track and sectors so that it is addressable by a DOS version; Syntax : C:\> format A:/s
9. Sys this command transfers MSDOS System files to specified areas to make the disk boo table; Syntax: C:\>Sys A:<
10 Pipes (|) it connects two files ie the standard output of one filter command becomes standard input of another filter; eg Dir/Sort/ more ||
11. Batchfiles all batch files on DOS must have the file extn on bat to execute the batch file, the user has just type the file name and press enter key, in addition to usual DOS command.
12. Echo this command can be used to display a message on the screen
13. Pause when this command is obeyed, the system waits for the user to press a key by displaying a line “strike a key when ready”
14. Rem a command or remark can be used on batch file by the rem command; to symbol @ can be put in a REM command to prevent DOS from displaying the commend during the execution of batch files.