1. Mostly MS Dos with some UNIX/LINUX
The Command Line
Mostly MS Dos with some UNIX/LINUX
Copyright © Curt Hill

2. Introduction
The command line interface is a modified time-sharing command interface
Predates GUIs
Still important for sophisticated professionals such as Software Engineers
Microsoft has been trying to remove it from Windows since before XP
Much of what you have seen hides the command line stuff
Copyright © Curt Hill

3. Brief History First time sharing systems are in 1960s
Enter a command from a printing terminal
Central CPU executes
UNIX developed in early 1970s
Command format is the name of any program followed by parameters
DOS 1 adopts this approach
Single user
Syntax modifications
Copyright © Curt Hill

4. Contrast
Current Windows believes in two different styles of executables
A GUI oriented one and a console oriented one
The GUI executable registers its controls and event handlers as its first order of business
By default it does not have a console
A console executable does have a console
It immediately starts to do the work involved
Copyright © Curt Hill

5. Shells
The notion of a shell dates back to early versions of UNIX or before
A shell is a command interpreter
It gave an interactive means for a user to use the system
UNIX allowed anyone to create their own shell, while Windows was less forthcoming in this respect
On most previous versions of Windows this is the DOS command prompt – now it is PowerShell
Copyright © Curt Hill

6. Shell Scripts
If the shell can accept commands from a file instead of the console this is called a shell script
UNIX has a command redirection feature that enabled this
The > and < on the prompt
A shell script is a full but simple programming language with variables, flow of control and other features we expect in programming languages
Copyright © Curt Hill

7. The Console Often called the DOS box
Only interface DOS had
Recently PowerShell became the default console
Paradigm is that of a printing terminal or glass teletype
Sequence of lines produced by program and user
Minimal editing of the line
Recall previous typed line and backspace
Copyright © Curt Hill

8. Command sequence Machine gives a prompt
Usually a C:...> with blinking cursor
You answer with Command and <CR>
If the command is valid it is executed
When command is done go back to prompt
Copyright © Curt Hill

9. Command format A command has this format
CMD parameters and files
A command must be properly spelled
A parameter is some extra info to the command
DOS standard starts with a slash (/)
UNIX standard starts with a dash (-)
Most are optional
In Windows it is the program itself that determines the format of the parameter
Copyright © Curt Hill

10. Programs The DOS box is actually cmd.exe in the Windows directory
PowerShell is powershell.exe
UNIX/LINUX calls this thing a shell
It has a variety of shells
Consistent with the UNIX philosophy
Whether a DOS box or UNIX shell they are all command interpreters
In early versions they were only command interpreter
Now the GUI part interprets some commands
Copyright © Curt Hill

11. File specification How do we specify a file? In DOS In UNIX
Files have several pieces for their name
In DOS
File name
File extension
File directory
In UNIX
The extension is just part of the name
A dot is an ordinary character
Copyright © Curt Hill

12. File name Originally 1-8 characters Name is composed of
Now they may be much larger
Name is composed of
Letters
Digits
Specials
Only characters that have special meaning in DOS may not be used
Name should identify the particular project
UNIX is a little more restrictive
Copyright © Curt Hill

13. File type or extension Originally 0-3 characters
Now may be more
Separated by a dot from name
Used to describe the kind of stuff in the file
Predefined extensions
.exe - program
.bmp – bitmap picture
.bat - DOS batch file
A batch file will be discussed later
.ps1 – PowerShell script
Copyright © Curt Hill

14. File Directory Combination of the disk letter and subdirectory
In Windows/DOS disk is a letter followed by a colon
In UNIX disk are represented by load points that are named not lettered
Directories and subdirectories are delimited by \ in DOS and / in UNIX
These may be discussed in a subsequent presentation
Copyright © Curt Hill

15. Defaults
By default if subdirectory is not specified the current disk and directory are used
These may be shown in the prompt
The form of the prompt may be set by the user
Extension
Certain programs require certain extensions
Each program may assume an extension or not
Copyright © Curt Hill

16. Wildcards
Wildcards are ways to specify a whole group of files at once because of similarity of name
* - matches as many characters as possible
No characters need follow it until a .
? - matches one and only one character
Wildcards are often interpreted by the program so usage varies
Copyright © Curt Hill

17. The C/C++ main function
The standard main function looks like this: int main(int argc, char *argv[])
The initial int is the return value
Argc is a count of command line parameters
Argv is an array of character strings
The actual command line parameters
The program needs to interpret these as it sees fit
Copyright © Curt Hill

18. Parsing the command
Def: to parse is to understand the form and meaning of communication or describe the form, function and relationships of a sentence
How does DOS determine what to do with the command?
Lets look
Copyright © Curt Hill

19. Executable Location
Where can an executable be and be found in the command prompt?
You would think that executables must be the Windows directory or one of the Program Files directories
This is partially, but not fully true
Executables must be on the Path
The Path is an environment variable
Copyright © Curt Hill

20. Environment Variables
A set of name value pairs that affect how things operate
Both Windows and UNIX have the concept
Both systems have a TEMP variable which identifies a directory where a program may create temporary files
Both also have the PATH variable
Copyright © Curt Hill

21. The Path The Path environment variable is a string of directory names
When a command needs an executable the Path directories are searched
If there are multiple files of the same name, the first one found is used
Windows has two paths
A global one for all users
A local one for each user
The two are merged
Copyright © Curt Hill

22. Finding the Path
Like all good Windows options there are multiple ways to examine or set
Control Panel / System
Advanced System Settings
Copyright © Curt Hill

23. Advanced
Copyright © Curt Hill

24. Environment Variables
Copyright © Curt Hill

25. Command Interpretation
Suppose that at the prompt the command: XYZ /z abc.def is entered – what happens?
The first word is the command name
This may be prefixed by the disk, subdirectory etc.
xyz is assumed to be name of command and /z and abc.def is passed to the command for inspection
Copyright © Curt Hill

26. Search for command 1
First the internal commands are searched for this command
The internal commands are in the command processor
They do not have file representations
They include dir, type, ren, del, copy, etc
If it is found then it is executed, otherwise the search continues
Copyright © Curt Hill

27. Search 2 Next we look in the current directory
There are two extensions that can be executed:
.EXE
.BAT
They will be searched in that order: first xyz.exe and finally xyz.bat
There used to be a .com format as well
If they are not found there, then the path is checked
The order of the directories in the path command is then the order they will be searched
Copyright © Curt Hill

28. Path searches
Like in the current directory, the first directory on the path is searched for xyz.exe and then xyz.bat
Only if it is not found do we go to the second and subsequent directories
If all the directories are searched and the command is not found, then we declare that this is an unknown file or command
Copyright © Curt Hill

29. Advantages
The OS does not distinguish between its own external commands and foreign commands
Internal commands have an advantage over other commands
However external commands are just files like any other
If we want to redefine we can
If we want to write a new kind of command that makes life easier all we have to do is put it on the path
Copyright © Curt Hill

30. Commands We next want to consider various commands that may be useful
These are typically file manipulation command
Any executable can be used
If it generates a window it may still be started from the command line
Windows distinguishes between GUI and non-GUI executables
Copyright © Curt Hill

31. DIR Short for directory Displays the files present in the local
Command alone shows all files in current directory
You may also use file names and wild cards
DIR is an internal command
UNIX used ls with different options
Copyright © Curt Hill

32. Parameters The typical parameter of a command is a file
Certain commands may take wildcards
The internal commands usually have options started with /
The option /? will give a page showing the format and options
Non MS programs may have /h or /help instead
Next screen shows this for dir
Copyright © Curt Hill

33. Dir options
Copyright © Curt Hill

34. COPY Make an identical copy of a file COPY source destination
COPY a.dat b.dat
Make a copy of a.dat
Same disk, directory, etc
Retains same date as the a.dat
UNIX uses cp with different options
Copyright © Curt Hill

35. Copy Again
Accepts wildcards in source file and matching in destination
COPY must give it a new name or copy it elsewhere, since a directory can only have 1 identically named item
Concatenation of files is allowed using + between file specs for source
COPY b.dat+c.dat all.dat
Copyright © Curt Hill

36. DEL (ERASE) Removes the file from the disk Accepts wildcards DEL *.bak
UNIX uses rm with different options
Copyright © Curt Hill

37. RENAME Gives a new name May abbreviate to REN May use wildcards
UNIX uses mv which moves rather than renames
A rename is move to same location with different name
Copyright © Curt Hill

38. The Screen
The DOS screen emulates the printing terminal or glass teletype
It displays the lines you typed in as well as the responses that the commands provided
Since it is in its own window we can use the scrollbar and see that which happened before
The CLS command will clear it
Copyright © Curt Hill

39. Cursor Keys We may use the cursor keys to modify the current command
The left and right keys allows moving in the current command
The delete and backspace change
Insert toggles whether characters are inserted or overwritten
Using the up and down key moves us through the list of commands we have used
Makes it easier to reuse the typing of a previous command
Copyright © Curt Hill

40. Help command
DOS still retains the HELP command which will show the commands that exist
Following the HELP you may also specify the command that you wish to know more about, such as:
HELP COPY
Copyright © Curt Hill

41. Directory Commands Cd or chdir changes the current directory
Md or mkdir creates a new directory
Rd or rmdir destroys
The directory name follows the command
Two specials
Single dot refers to the current directory
Two dots refers the ancestral
Copyright © Curt Hill

42. Addendum: Long file names
The original FAT file system believed only in the 8.3 name
Later, long file names were allowed
These also allowed blanks as a valid character
There was an algorithm that would convert that long name into an 8.3 name
This produced two versions of the name that co-existed
The 8.3 name always had a tilde ~ in it
Copyright © Curt Hill

43. Blanks
The command processor has been modified to handle the blanks in a name
A long file name may be enclosed in double quotes
Then even if it has blanks it can be processed
Another trick that helped is for the CD command
A tab will fill in one of the available directories
Copyright © Curt Hill

44. Conclusion We now have the basics
Next we learn about redirection, pipes and standard files
Then batch files briefly
We restart with PowerShell
Copyright © Curt Hill