#unix command

Top 10 tar command example in unix

In Unix, tar command is useful as it can combine several files into a single uncompressed file and save space in unix. Tar command, also called tape archiving, can combine several files together and can create an archive folder  and it can be zipped as well. Later on we can extract file from  archived file as well. In below unix tutorial , we will go through some of important tar command example…

vi command in unix with example

vi is a screen-oriented text editor originally created for the Unix operating system. In below article we will go through vi command in unix with example . We will learn different mode of vi editor and how we can use different option while using vi command to edit files in unix.

vi command in unix with Example Modes of VI command:

There are essentially three Modes in vi,

Insert Mode :To insert or…

find command in unix with example

Find command in unix with example : As name suggest , find command in unix give us option to search file based on certain parameter. By combining other command with find command , we can perform some action also on searched list of files. Here we will go through various type of Find command in unix with example .

find command in unix with example

find command in unix with example 1. Unix find…

The history of grep, the 40 years old Unix command

The history of grep, the 40 years old Unix command

  grep is a Unix command line utility (well most Unix utilities are command line) that searches the input files for pattern and prints lines that contain the pattern. If you are reading this you, you are probably no stranger to grep.

grep was written by Ken Thompson, the same guy who wrote Unix. grep first appeared in Unix v4with limited features…

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

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:

2.1 Copying Files

cp (copy)

cp file1 file2 is the command which makes a copy of file1 in the current working directory and calls it file2

First we need a file to work with. You can get a copy of the file. If you are using a three button mouse, right-click here and select 'Save Linked File As...'. If you don't have a three button mouse you will have to hold down [Ctrl] key while you click. Save the file into your unixstuff directory with the name science.txt.

Now we can make a backup copy of science.txt by copying it to a file called science.bak. First, cd to your unixstuff directory.

$ cd ~/unixstuff

Then at the UNIX prompt, type,

$ cp science.txt science.bak

2.2 Moving files

mv (move)

mv file1 file2 moves (or renames) file1 to file2

To move a file from one place to another, use the mv command. This has the effect of moving rather than copying the file, so you end up with only one file rather than two.

It can also be used to rename a file, by moving the file to the same directory, but giving it a different name.

We are now going to move the file science.bak to your backup directory.

First, change directories to your unixstuff directory (can you remember how?). Then, inside the unixstuff directory, type

$ mv science.bak backups/.

Type ls and ls backups to see if it has worked.

2.3 Removing files and directories

rm (remove), rmdir (remove directory)

To delete (remove) a file, use the rm command. As an example, we are going to create a copy of the science.txt file then delete it.

Inside your unixstuff directory, type

$ cp science.txt tempfile.txt $ ls (to check if it has created the file) $ rm tempfile.txt  $ ls (to check if it has deleted the file)

You can use the rmdir command to remove a directory (make sure it is empty first). Try to remove the backups directory. You will not be able to since UNIX will not let you remove a non-empty directory.

Exercise 2b

Create a directory called tempstuff using mkdir , then remove it using the rmdir command.

2.4 Displaying the contents of a file on the screen

clear (clear screen)

Before you start the next section, you may like to clear the terminal window of the previous commands so the output of the following commands can be clearly understood.

At the prompt, type

$ clear

This will clear all text and leave you with the $ prompt at the top of the window.

cat (concatenate)

The command cat can be used to display the contents of a file on the screen. Type:

$ cat science.txt

As you can see, the file is longer than than the size of the window, so it scrolls past making it unreadable.

less

The command less writes the contents of a file onto the screen a page at a time. Type

$ less science.txt

Press the [space-bar] if you want to see another page, type [q] if you want to quit reading. As you can see, less is used in preference to cat for long files.

head

The head command writes the first ten lines of a file to the screen.

First clear the screen then type

$ head science.txt

Then type

$ head -5 science.txt

What difference did the -5 do to the head command?

tail

The tail command writes the last ten lines of a file to the screen.

Clear the screen and type

$ tail science.txt

How can you view the last 15 lines of the file?

2.5 Searching the contents of a file

Simple searching using less

Using less, you can search though a text file for a keyword (pattern). For example, to search through science.txt for the word 'science', type

$ less science.txt

then, still in less (i.e. don't press [q] to quit), type a forward slash [/] followed by the word to search

/science

As you can see, less finds and highlights the keyword. Type [n] to search for the next occurrence of the word.

grep (don't ask why it is called grep)

grep is one of many standard UNIX utilities. It searches files for specified words or patterns. First clear the screen, then type

$ grep science science.txt

As you can see, grep has printed out each line containing the word science.

Or has it????

Try typing

$ grep Science science.txt

The grep command is case sensitive; it distinguishes between Science and science.

To ignore upper/lower case distinctions, use the -i option, i.e. type

$ grep -i science science.txt

To search for a phrase or pattern, you must enclose it in single quotes (the apostrophe symbol). For example to search for spinning top, type

$ grep -i 'spinning top' science.txt

Some of the other options of grep are:

-v display those lines that do NOT match  -n precede each matching line with the line number  -c print only the total count of matched lines 

Try some of them and see the different results. Don't forget, you can use more than one option at a time, for example, the number of lines without the words science or Science is

$ grep -ivc science science.txt

wc (word count)

A handy little utility is the wc command, short for word count. To do a word count on science.txt, type

$ wc -w science.txt

To find out how many lines the file has, type

1.1 Listing files and directories

ls (list)

When you first login, your current working directory is your home directory. Your home directory has the same name as your user-name, for example, j_burns, and it is where your personal files and subdirectories are saved.

To find out what is in your home directory, type

$ ls (short for list)

The ls command lists the contents of your current working directory.

There may be no files visible in your home directory, in which case, the UNIX prompt will be returned. Alternatively, there may already be some files inserted by the System Administrator when your account was created.

ls does not, in fact, cause all the files in your home directory to be listed, but only those ones whose name does not begin with a dot (.) Files beginning with a dot (.) are known as hidden files and usually contain important program configuration information. They are hidden because you should not change them unless you are very familiar with UNIX!!!

To list all files in your home directory including those whose names begin with a dot, type

$ ls -a

ls is an example of a command which can take options: -a is an example of an option. The options change the behavior of the command. There are online manual pages that tell you which options a particular command can take, and how each option modifies the behavior of the command. (See later in this tutorial)

1.2 Making Directories

mkdir (make directory)

We will now make a subdirectory in your home directory to hold the files you will be creating and using in the course of this tutorial. To make a subdirectory called unixstuff in your current working directory type

$ mkdir unixstuff

To see the directory you have just created, type

$ ls

1.3 Changing to a different directory 

cd (change directory)

The command cd directory means change the current working directory to 'directory'. The current working directory may be thought of as the directory you are in, i.e. your current position in the file-system tree.

To change to the directory you have just made, type

$ cd unixstuff

Type ls to see the contents (which should be empty)

Exercise 1a

Make another directory inside the unixstuff directory called backups

1.4 The directories . and ..

Still in the unixstuff directory, type

$ ls -a

As you can see, in the unixstuff directory (and in all other directories), there are two special directories called (.) and (..)

In UNIX, (.) means the current directory, so typing

$ cd .

NOTE: there is a space between cd and the dot

means stay where you are (the unixstuff directory).

This may not seem very useful at first, but using (.) as the name of the current directory will save a lot of typing, as we shall see later in the tutorial.

(..) means the parent of the current directory, so typing

$ cd ..

will take you one directory up the hierarchy (back to your home directory). Try it now.

Note: typing cd with no argument always returns you to your home directory. This is very useful if you are lost in the file system.

1.5 Pathnames

pwd (print working directory)

Pathnames enable you to work out where you are in relation to the whole file-system. For example, to find out the absolute pathname of your home-directory, type cd to get back to your home-directory and then type

$ pwd

The full pathname will look something like this -

/Users/j_burns

which means that j_burns (your home directory) is in the directory Users (the directory containing all user directories), which is located in the root directory (the root directory is indicated by the leading slash '/').

  Exercise 1b

Use the commands ls, pwd and cd to explore the file system.

(Remember, if you get lost, type cd by itself to return to your home-directory)

1.6 More about home directories and pathnames

Understanding pathnames

First type cd to get back to your home-directory, then type

$ ls unixstuff

to list the contents of your unixstuff directory.

Now type

$ ls backups

You will get a message like this -

backups: No such file or directory

The reason is, backups is not in your current working directory. To use a command on a file (or directory) not in the current working directory (the directory you are currently in), you must either cd to the correct directory, or specify its full pathname. To list the contents of your backups directory, you must type

$ ls unixstuff/backups

~ (your home directory)

Home directories can also be referred to by the tilde ~ character. It can be used to specify paths starting at your home directory. So typing

$ ls ~/unixstuff

will list the contents of your unixstuff directory, no matter where you currently are in the file system.

What do you think

$ ls ~

would list?

What do you think

$ ls ~/..