#basic unix commands

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What is Unix ?

The Unix system is a multi-user, multi tasking operating system which means that it allows a single or multiprocessor computer to simultaneously execute several programs by one or several users. It has one or several command interpreters (shell) as well as a great number of commands and many utilities (assembler, compilers for many languages, text processing, email, etc.). Furthermore, it is highly portable, which means that it is possible to implement a Unix system on almost all hardware platforms.

Check out Unix Tutorial for more

The history of UNIX systems

The first "Unix" system was developed by Ken Thompson in the Bell AT&T laboratories at Murray Hill in New Jersey in the United States from 1965. Ken Thompson's aim was to develop a simple interactive operating system, called "Multics" (Multiplexed Information and Computing System) in order to run a game which he had created (space travel, a simulation of the solar system).

A consortium made up of MIT (Massachesetts Institute of Technology), General Electric Co. and Bell Lab was then formed around Multics.

In April 1969 the AT&T laboratories decided to use the GECOS (General Electric Comprehensive Operating System ) instead of Multics. However, Ken Thompson and Dennis Ritchie who joined the team needed to make the space travel game work on a smaller machine (a DEC PDP-7, Programmed Data Processor which only had 4K of memory to make user programs run), this is why they recreated the system in order to create a limited version of Multics called UNICS (UNiplexed Information and Computing Service), quickly shortened to Unix.

The date of 1st January 1970 is considered as the birth date of the UNIX system, which explains why all system clocks for Unix operating systems start from this date.

Alongside these activities, D.Ritchie played a large part in the definition of the C language (since he is considered as one of its creators with B.W.Kernighan), so the whole system was entirely rewritten in C in 1973 and called Unix Time-Sharing System (TSS).

Basic UNIX Commands

Use the following commands to help you manage your UNIX account.

IMPORTANT:

The UNIX (Ultrix) operating system is case se

nsitive. All commands must be typed in lower-case

letters unless noted otherwise.

Displaying a Directory

ls

-- Lists the names of files in a particular

UNIX directory. If you type the ls command

with no parameters or qualifiers, the co

mmand

displays the files listed in your current working directory. When you give the ls command, you can add one or more modifiers to

get

additional information.

Example:

ls

Result: Lists the names of files in your de

fault directory, in alphabetical order.

Example:

ls -l

Result: Gives a "long listing" of the files in

your directory. In addition to the f

ile name, the long listing shows protection

information,

file owner, number of characters

in file, and the date and time of the last change to the file.

Example:

ls -a

Result: Causes all your files to be listed, including thos

e files that begin with a period (i.e., hidden files).

For more information, type

man ls

at the UNIX system prompt.

Displaying and Concaten

ating (Combining) Files

more

-- Enables examination of a continuous text one screenful at

a time on a terminal. It normally

pauses after each screenful,

printing -- More -- at the bottom of the screen. Press

<RETURN>

to display one more line. Press the

<SPACE BAR>

to display

another screenful. Press the letter Q to stop displaying the file.

Example:

more newfile

Result: Displays the contents of “newf

ile” one screen ("page") at a time.

For more information about this command, type

man more

at the UNIX system prompt.

cat

-- Displays the contents of a file on your terminal.

Example:

cat newfile

Result: Displays the contents of th

e file “newfile” on your terminal.

Example:

cat newfile oldfile

Result: Displays the contents of two files -- “newfile” and

“oldfile” -- on your terminal as one continuous display.

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Unix Commands

Unix commands have the general format:

command [options] [item]

Items in brackets are optional, and words in italics are generic identifiers (i.e. options must be replaced by a particular option, e.g. -a).

Note that:

Unix Commands are case sensitive. The command ls is different from LS. In fact LS is not recognised as a valid command.

Command options consist of a single character. The command to list all the files in a directory is ls -a and could not be ls -all (the latter would have to mean a combination of options.)

Unix command options can usually be combined or listed separately. For example:

ls -al or ls -a -l

The command item is given last. This is very often a file name. For example:

ls -a file1.f not ls file1.f -a

The echo command

The echo command 'echoes' its argument to the standard output. This means that in its simplest form it prints something out on screen. For example:

% echo Hello - you type Hello - response from the shell%

Who is logged on?

The command who gives a list of logged on users:

% who root console Jan 4 10:34 men6matw ttyp1 Jan 6 09:45 (ecusun1) cbl6nd ttyp2 Jan 6 10:10 (cblslcd) cbl6ar ttyp3 Jan 6 16:03 (cblsuna) csc6ea ttyp4 Jan 6 14:15 (csuna1) root ttyp5 Jan 6 10:40 (sun032) ecl6rsh ttyp6 Jan 6 15:39 csc6ea ttyp8 Jan 6 14:15 (csuna1) lnp5mw ttyUf Jan 6 16:16 lnp5jb ttyp3 Jan 6 15:20 (sun051)

Also try the command finger. This command gives the full name of logged in users.

PRACTICE

Type finger to get information on yourself and other users.

Creating a directory

Themkdircommand is used to create directories. The format of this command is:

% mkdir directory_name

Jenny Brown stores her unix scripts in a directory called scripts beneath her home directory. In order to create this directory she uses the command:

% mkdir scripts

Deleting a directory

Thermdircommand is used to delete directories. The format of this command is:

% rmdir directory_name

Jenny Brown stores files for project work in a directory called proj. When the project has been completed she deletes the directory using the command:

% rmdir proj

Note that the directory must be empty before it can be deleted.

Listing contents of a directory

The commandlsis used to list the contents of a directory. For example:

% ls file1 scripts test.f test

Notice that directories are listed as well as files. To list all files, including hidden files, give the command:

% ls -a .cshrc file1 bin test.f test

Hidden files begin with . (a full stop). Hidden files are normally system files, and will normally include the following:

% ls -a .cshrc .forward .history .login .logout

.cshrc contains commands that are executed every time you start off a C-shell, including when you log in

.forward enables you to redirect your mail to another computer

.history contains a record of previously executed commands

.login contains commands that are executed at login time

.logout contains commands that are executed at logout time

The purpose of some hidden files.

To identify directories in a listing give the command:

% ls -F file1 bin/ test.f test

Notice how the directory is identified by the slash (/) character.

Deleting files

Files can be deleted using the rm command. For example:

% rm test.f

Displaying files

The command cat is used to display the contents of a file on the screen.

For example:

% cat file1

Creating files

The command cat can also be used to create a file. For example:

% cat > test.f When typing in a new file the input must be terminated by ^D

NOTE^D means press the <ctrl> and the d keys simultaneously. Be careful not to type ^D when you have the shell prompt, because this might log you out. Normally you would use an editor for creating files. This example is given since it illustrates how to create a small file without needing to learn the use of an editor.

Copying files

The command cp is used to copy a file. It takes the format:

% cp old_file new_file

For example:

% cp file1 file2

Renaming files

The command mv is used to rename a file.

For example:

% mv file2 temp

changes the name of file2 to temp.

More Linux Commands

Moving files

The command mv is also used to move a file to a new location in the filestore hierarchy. For example:

% mv file2 bin

moves the file file2 into the subdirectory bin.

Overwriting files

Commands such as rm and cp can be dangerous if not used with care. The command:

% cp file1 file2

will delete file2 if a file of that name already exists. If you have spelled the name of the new file incorrectly you may accidentally overwrite the contents of a file. Using the wildcard symbol * with the command rm can also be very dangerous. The command:

% rm test*

will delete all files starting with test. However if you inadvertently type an extra space (do not try this!):

% rm test * -do not try this!

the file test will be deleted if it exists. Then all other files in the directory will be deleted! Often no warning will be given.

To prevent accidental deletion of files you can use the -i option with commands such as rm. The format of the command is:

% rm -i file

You will be asked to confirm that files are to be deleted. You may find that this is set as the default on your system.

Wildcards

Wildcard characters can be used to identify directory and file names. The wildcard character * is used to refer to any combination of characters. For example:

% ls * - refers to all files % cat test* - refers to all files starting with 'test', e.g. 'test', 'testing', 'test.c', etc.