External commands are known as Disk residence commands. Because they can be store with DOS directory or any disk which is used for getting these commands. Theses commands help to perform some specific task. These are stored in a secondary storage device. Some important external commands are given below-

1. MORE:-Using TYPE command we can see the content of any file. But if length of file is greater than 25 lines then remaining lines will scroll up. To overcome through this problem we uses MORE command. Using this command we can pause the display after each 25 lines.

Syntax:- C:\> TYPE <File name> | MORE
C:\> TYPE ROSE.TXT | MORE
or
C:\> DIR | MORE

2. MEM:-This command displays free and used amount of  memory in the computer.

Syntax:- C:\> MEM
the computer will display the amount of memory.

3. SYS:- This command is used for copy system files to any disk. The disk having system files are known as Bootable Disk, which are used for booting the computer.

Syntax:- C:\> SYS [Drive name]
C:\> SYS A:
System files transferred
This command will transfer the three main system files COMMAND.COM, IO.SYS, MSDOS.SYS to the floppy disk.

4. XCOPY:- When we need to copy a directory instant of a file from one location to another the we uses xcopy command. This command is much faster than copy command.

Syntax:- C:\> XCOPY < Source dirname >  <Target dirname>
C:\> XCOPY  TC TURBOC

5. MOVE:- Move command is used for moving one file or multiple files from one location to another location or from one disk to another disk.

Syntax:- C:\> MOVE  <file name>  <path name>
C:\SONGS> MOVE   *.MP3   C:\ SONGS\OLD SONGS\

C:\>

6. FC:-(File Compare) This command is capable for comparing two set of files and display difference between two files.

Syntax:- C:\> FC <First set of file>  <Second set of file>
C:\> FC ROSE.TXT GULAB.TXT

7.CHKDSK:-(Check disk) - This command is used to check the status of a disk and show the report of result status.

Syntax:- C:\> CHKDSK

C:\>CHKDSK CHKDSK has NOT checked this drive for errors. You must use SCANDISK to detect and fix errors on this drive. Volume JAI created 10-19-2001 7:14p Volume Serial Number is 3E42-1907 4,203,073,536 bytes total disk space 381,988,864 bytes available on disk 4,096 bytes in each allocation unit 1,026,141 total allocation units on disk 93,259 available allocation units on disk 651,264 total bytes memory 610,784 bytes free Instead of using CHKDSK, try using SCANDISK. SCANDISK can reliably detect and fix a much wider range of disk problems.

8. SORT:- This command is useful when we want to sort a file. When we run this command the result can be get to display device or file.

Syntax:- C:\> SORT /R  < Input file name>  <output file name>
Suppose we have a file Player.txt which having the list of a cricket player team and we want to sort the list of players, then we uses this command
C:\> SORT  Player.txt

If we not specify the output file name then result will show to the screen.

/R- switch is used for sorting the file in descending order like from Z to A or from 9 to 0.

9. FIND:- The FIND command is used to search a file for a text string. 

Syntax:- C:\> FIND "String to search" <File name>
C:\TEST>find "office" gulab.txt

---------- gulab.txt
A clock in a office can never get stolen

10. DISKCOPY:- DISKCOPY copies the contents of a floppy disk to another.

Syntax:- C:\> DISKCOPY  <Drive1>  <Drive2>
C:\> DISKCOPY  A:   B:

This command will be copy all contents of A drive to B drive.

11. ATTRIB:- Sets the various type of attribute to a file. Like Read only, Archive, Hidden and System attribute.

Syntax:- C:\> ATTRIB [± r] [± a] [± h] [± s] <File name>
here r  -  for read only,  a-  for archive, h  -  for hidden, s -  for hidden attribute.
C:\> ATTRIB +r  Gulab.txt
This command will change the attribute of file gulab.txt to read only mode. To remove the read only attribute we will follow this command.
C:\> ATTRIB -r Gulab.txt

12. LABEL:- If you are not happy with the volume label of hard disk, you can change it.

Syntax:- C:\> LABEL
C:\>LABEL
Volume in drive C is JAI
Volume Serial Number is 3E42-1907
Volume label (11 characters, ENTER for none)? INFOWAY

13. DOSKEY:- Once we install doskey , our dos will star to memorize all commands we uses. We can recall those commands using up or down arrow keys. It also gives the facility to create macros, which creates a short key for long keyword or command. 

Key function for Doskey are given as-

UP,DOWN	arrows recall commands
Esc	clears current command
F7	displays command history
Alt+F7	clears command history
F9	selects a command by number
Alt+F10	clears macro definitions

Syntax:- C:\> DOSKEY
DOSKey installed

Creating Macros:-
C:\>doskey t=time

C:\>t
C:\>time
Current time is 3:39:05.97p
Enter new time:

To list out all macros defined just type DOSKEY/MACROS at dos prompt and press enter.
C:\>DOSKEY/MACROS
$D=date
T=time

14. FORMAT:- This command creates new Track & Sectors in a disk. Every

Syntax:- C:\> FORMAT  [drive name] [/S]
C:\> FORMAT A:
this command will create new track & sectors.
C:\> FORMAT A: /S
This command will transfer system files after formatting the disk.

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