unix presentation 6 (24 jan 08)

8/7/2019 Unix Presentation 6 (24 Jan 08)

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In the todays session well read :-

What is command

Option Arguments File Arguments

Internal and External commands

The Basic commands of UNIX

date

clear and tput banner who cal ls

cat Conti.


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wc Feeding output of one command to another type path man uname tty

passwd lock echo cup smso and rmso bc Conti.

Conti.


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What is a Command

The UNIX system is heavily command-based i.e. you have to

type in a few characters to frame a command and then press the

enter key for it to work.

UNIX commands are executable files and built-in utility

programs.

All UNIX commands are case sensitive. Most commands are in

lower case.

Commands typically have the syntax:

command option(s) argument(s)Conti.


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Options :-

Modify the way that a command works.

Usually consist of a hyphen (-) followed by a single letter.

Some commands accept multiple options which can usuallybe grouped together after a single hyphen

A small number of commands require each option to begiven separately.

Should be separated from the command name by a space.

Conti.


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Arguments :-

Most commands are used together with one or morearguments.

Some commands assume a default argument if none issupplied.

Arguments are optional for some commands and required byothers.

In most cases, multiple arguments should be separated fromeach other by a space. They should be separated from the

command name and/or options by a space also.

Conti.


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FilenameArguments :- Many UNIX commands use a

filename as an argument so that the command can take input

from the file.

It is very general feature of the UNIX that some commandswork with more then one filename. For Ex.

$ ls -l chap01 chap02 chap03

The command with its arguments is entered in one line thatis referred to as the Command Line.

Conti.


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Internal and External Commands

Files or programs that have independent existence in the /bin

directory (or /usr/bin) are branded as an External command.

Ex. ls (external command)

Most commands are external in nature, but there are some

which are not really found anywhere and some which are

normally not executed even if they are in one of the directories

specified by PATH. For Ex. echo command.

$ type echo

o/p : echo is a shell built-in.

Cont.


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echo is not a external command in the sense that, when you

type echo the system wont look in its PATH to locate it.

Rather, it will execute it from its own set of built-in

These built-in commands, of which echo is a member are

known as Internal commands.

The shell, which itself is a command, processes its own set of

commands and even if theres a command of the same name in

/bin or /usr/bin, the shell will record top priority to its own

internal command of the same name.


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The BasicCommands of UNIX

date (Display The System Date):- date command that

combines the functions of the DATE and TIME commands of

DOS.

The command does not prompt you to change eitherthe date or the time. This facility is only available tothe administrator and the strange thing is that he uses

the same command.

For Ex.

$ date

The command can also be used with suitable formatspecifiers as arguments.

Conti.


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Conti.

There are other format specifier :

d day of the month (1 to 31)y last two digits of the year

H,M and S hour, minute and second respectively


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clear and tput (Clear your Screen):- There are two

commands available in most UNIX systems to clear your

screen.

For Ex.$clear

If you get the message clear : not found on your

screen, try the other command tput which is the original

agent of the UNIX system

For Ex.

$ tput

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tput requires some additional material to work properly. Toclear the screen, follow tput with the word clear

For Ex.

$ tput clear

Conti.


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banner (Display a Blown-Up Message) :- You can create

fancy objects on your screen with the banner command

For Ex.$ banner John lee

who (Login Details) :- The who command is there to tell you

who you are, so you should use it with two arguments am

and i :

$ who am I

If you want to see all user working on various terminalsthen simply write command.

For Ex. $ whoConti.

Conti.


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For printing column headers write command

$ who Hu

-u option provides more detailed list

who is regularly used by the system administrator tomonitor weathers terminals are being properly utilized.

Conti.

Conti.


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Conti.

cal :- cal is a handy tool that you can invoke any time to see

the calendar of any specific month or a complete year.

If you wish to see the calendar for the month of Decemberyou can provide this as an argument to cal :

$cal dec

$cal 1998 will print whole year moths. In this commandfor stop scrolling you have to use and

to resume it.

Instead of using for stop scrolling and toresume it we can also use this command :-


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For Ex.

$cal 1998 | more

ls :- This command is used to list out the names of the files

available in current directory.

$ ls

If this command is showing 6 file with 3 file starting letterchap then we can also sort out these file by followingcommand :-

$ ls chap*

Conti.

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Conti.

For knowing some information about the list of files wecan use option with argument.

For ex.$ ls l chap*

Here (hyphen) is option

l is argument

cat (Displaying and createing files):- For showing contents

of any particular file

For Ex.

$cat filename Conti.


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Unix has simple symbols (called operator) for creating andstoring information in file.

Instead of viewing the output of ls command on theterminal, we can save the information in the file list (file

name) using a

special symbol >

For Ex.

$ ls > filename(say list)

This mechanism is called redirecting any output normallycoming to the terminal to a disk file.

Conti.


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-l option counts the number of lines :$ wc -l infile

-w option counts the number of words :$ wc -w infile

-c option counts the number of characters :$ wc -c infile

We can also count number of lines, words and characters ofmultiple files :

For Ex.

$ wc infile1 infile2 infile3

Conti.


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Conti.

Feeding output ofOne command to another :- This concept is

done by special symbol | (pipe)

For Ex.

$ ls | wc

will simply connecting the output of ls to the input of wc

type :- The best and fastest way to know the location of any

command in the UNIX inbuilt file system is type.

For Ex.

$ type ls


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Path :- The sequence of directories that the system will search to

look for a command is specified in its own PATH variable. To

find a directory list separated by colons well write :

$ echo $PATH

man (On-line Help):- UNIX offers an on-line facility with the

man command.

For Ex. for help on the command wc you simply have to enter

$ man wc

Conti


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-k :- The -k option accepts the keyword and man then givesyou the name and short description from all manual sections

that contain the keyword.

For Ex. :

$ man -k inode

Linux also offers - -help command

Conti.


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uname (Know Your Machines Name):- This command is used

to see version of UNIX OS. For Ex. :

$ uname -r

If your machine is connected to a network, then it must havea name. If your network is connected to the Internet, then

name is required to frame your machines domain name. The

uname command with the -n option tells you the machine

name in a network

For Ex.

$ uname -n

Conti.


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tty (Knowing Your Terminal):- Since UNIX treats even

terminals as files, it is reasonable to expect a command, an

obvious that tells you the filename of the terminal you are using.

It is the tty (teletype) command which tell you this thing. Itrequires no argument.

For Ex.

$ tty/dev/tty01

The terminal filename is tty01 resident in the /dev directory.

If sumit logs in from another terminal next time his terminaldevice name will be different.

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Changing Your Password

passwd (Change your Password) :- Your password is

important; it stops other users from gaining access to your

account. Never give your password to anyone.

You should change your initial password very soon after yourfirst login.

To change your password: enter the command passwd and then

respond to the prompts by entering your old password followed

by your new one. You are then asked to retype your password

for confirmation. Note that what you type will not appear onthe screen for security reasons.For example: $ passwdOld password: - enter your current password

New password: - enter your new passwordRet e new assword: - re-enter our new assword


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Conti.

echo (Display Message) :- This command will print any

message given in its arguments

For Ex.

$ echo Sco Unix

O/P will be : Sco Unix

For Sco Unix output write command :$ echo Sco Unix

cup (Taming the Cursor) :- This command is used to position

the cursor at row number 10 and column 20

For Ex. : tput cup 10 20


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smso :- This command is used for bold face your text by using

the smso and rmso.

For Ex.

$ tput smso$ echo Come to the Web

$ tput rmso

bc (The Calculator) :- This command is used as a calculator

For Ex.$ bc

For each calculation you have to press enter key and for

quitting from calculator press

Conti.


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Conti.

calendar :- The calendar command provides an useful

reminder mechanism for a user.

For Ex.

$cat calendar

The format mm-dd-yy or dd/mm/yy isnt recognized bycalendar as a valid date. Only mm/dd/yy is acceptable.

spell (Check your spelling) :- This command takes the nameof the file as a argument and generates a list of all spelling that

the program recognizes as mistake.

For Ex. :

$ spell linux.txt Conti


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By default spelling are checked with reference to the USdictionary, but you can use the -b (British) option to use a

different one :

For Ex.

$ spell -b

Linux has ispell command.

Conti.


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Script (Record Your Session) :- All the commands, their

output and error messages are stored in the file for later

viewing. If you wish you stored all activities done by you then

you should write script command for recording.For Ex.

$ script

Script started, file is typescript

$_

For viewing contents of this file you have to exit from script

then type cat and typescript command on shell prompt.


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time (Timing Processes) :- When faced with several versions

of a program, it becomes necessary to find out drainage that the

command makes on the system resources. The time command

does this work.

It accepts the command to be timed as its argument and thennot only executes the program but displays the time usage in

the terminal as well.

This enables the programmer to tune their programs so thatCPU usage is kept at an optimum level.

For ex. You can find out the time taken to perform a sortingoperation by preceding the sort command. Conti


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$ time sort -o a1

o/p : real 0m1.18s

user 0m0.73ssys 0m0.38s

The real time shown is the clock elapsed time from theinvocation of the command till its termination. The time can

differ on multi-user systems where several programs may be

running concurrently.

The user time shows the time spent by the program in

executing itself. Conti

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Conti.

The sys time indicates the time used by the UNIX system indoing work on behalf of the user.

The sum of user time and system time actually represents theCPU time and its not necessary that this time be equal to the

real time or clock elapsed time (as you see in present case).

Since some time is consumed in doing other work in the

system. The more heavily loaded a system is the greater is the

difference.


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End ofChapter 1

unix presentation 6 (24 jan 08)

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