wecome to unix

8/11/2019 Wecome to UNIX

1/40


2/40

Course Outline Introduction Logging On and Off

Unix File System Structure

Dealing with Directories Handling Files

Shell Basics

Shell Programming

Customisation


3/40

Introduction Unix operating system first Version was developedin 1969 by Ken Thompson in assembly language. In1973 UNIX was written in C language.

Unix is more powerful, more reliable, can do muchmore work, much faster and you do not need toreboot your computer everyday.

Best part about UNIX in C was portability


4/40

Features of Unix

A multitasking and multiuser system Each user has his/her own usernameor id

Many users can log in simultaneously

Access to files and programs is based on username

Each user may run multiple tasks


5/40

Logging On Users must identify themselves to the system

this is called logging on

At the login:prompt enter your idthen pressEnter(or return)

Atthepassword:prompt enter your passwordnote that you cannot see what you are typing

Change your password with thepasswd

command


6/40

Logging Off Disconnecting from the system is called logging off

Varies from system to system

exit logout

^D


7/40

Unix File System Organised as an inverted treeof directories

Begins at theroot /

Directories contain files and other directories Every user is allocated a home directory


8/40

Paths and PathnamesApathname(orpath)is a route from the root to the

file or directory in question

Directory names are separated by /s

A path beginning with a / is an absolutepath

A path beginning with anything but a / is a relativepath


9/40

Working Directories and Pathnames Relative paths are based upon the current working

directory

Change the working directory with the cdcommand

Show the working directory with thepwdcommand

List the contents of the working directory with thelscommand


10/40


11/40

Inodes Data structure to store administrative information

about a regular file, directory, or other filesystem object

Permission

Time stamps last modified, last used & last changed(inode)

Disk location Represented by a number called I-Number(ls i)


12/40

Creating and Removing DirectoriesA new directory can be created with the mkdir

command

Note that this cannot be shortened to md

A directory can be removed using the rmdircommand

The directory must be empty (no files or subdirectories)

The name cannot be shortened to rd


13/40

Manipulating Files Files are usually created by editors, compilers etc. rmremoves files (and directories)

cpcopies files (and directories)

mvmoves (renames) files (and directories) lslists files (not the contents of files)

cat displays


14/40

Wildcard ExpressionsWe often wish to apply a command to a selection of

files or directories

The shell wildcardfeature allows this ls *.c

lists all files whose names end in .c


15/40

Wildcard ExpressionsWhen we type in a wildcard expression it isexpanded by the shellbefore the command runs

If we type is ls *.cand the working directory

containsprog1.c, abc.candxyz.c then the actualcommand is

ls abc.c prog1.c xyz.c

The wildcard expression has been expanded in place


16/40

Wildcard Characters ? matches any character

* matches any number of characters

[abc] matches any of the characters in the

brackets [!abc] matches anything exceptthe characters in

the brackets

[a-z] matches the range of characters in the

brackets


17/40

Wildcard Examples abc?def

matches abcXdef, abc.def, abc3def but notabcdef

abc*

matches abc. abcd, abcdef, abc.another.part *.*

matches any name with a .


18/40

Wildcard Examples *

matches any name (except a name beginning with a.)

[abc]def matches adef, bdef and cdef

[a-z]*

matches any name beginning with a lower-case letter


19/40

Wildcard Examples

[a-zA-Z]*

any name beginning with an alphabetic character

[!a-zA-Z]*

any name beginning with a non-alphabetic character

[a-z]*[!A-Z]

any name beginning with a lower-case letter andending with anything except an uppercase letter


20/40

Avoiding Wildcard Expansion

Sometimes it is necessary to enter a wildcardcharacter on a command line, but not have itexpanded

Quote the argument containing the character ls abc*def

ls the file whose name is abc*def (if the system allows sucha name)

ls abc*def the same


21/40

Avoiding Wildcard Expansion

Escape the character

ls abc\*def

again lists the file whose name is abc*def

These can be used in combination echo Im a * and \* matches *

* inside the double quotes is not expanded

* after the \ is not expanded

only the final asterisk is expanded


22/40

File Permissions

Unix provides three distinct permissions for files:

read permission to examine the contents of a file

write permission to alter the contents of a file

execute permission to run a file as a program or shellscript


23/40

Directory Permissions

The same permissions apply to directories, but withdifferent meanings:

read permission to look at the contents of

the directory, i.e. to see file names write permission to create or delete files

within the directory

execute permission to execute (permission to list)


24/40

Listing Permissions

the -l(long) argument to the lscommand listspermissions

-rw-rw-rw- a file with read and write for the owner, group and

world

drwxr-xr-x a directory with read/write/execute for the owner,

read/execute for group and world


25/40

Setting Permissionschmod

The chmod (change mode) command sets and unsetsfile and directory permissions

chmod mode filename(s)

wheremodecan be:

who op permission op2 permission2 ...

octalnumber


26/40

Permissions the Quick Way

chmodalso allows octal representation

chmod 755 directory

Set rwx for owner, rx for group and world

chmod 644 file

Set rw for owner, r for group and world

chmod 711 file

Set rwx for owner, x for group and world


27/40

Creating Files

Most human-readable files on Unix are created with atext editor

Unix has many, many different editors

ed a very old line-oriented editor

ex an enhanced version of ed

vi the most ``popular editor a

Visual Interface to ex


28/40

The vi Editor Created by Bill Joy at UCB

Holds file being edited as an internal buffer

Screen acts as a windowonto the buffer

Operates in two basic modes Command mode

Insert mode


29/40

Starting vi vi

Starts viwith an empty buffer

vi file

Starts vi opensfilefor editing vi +n file

Starts viopensfileat line n

vi +/pattern file

Starts viopensfileat the first line matchingpattern vialways starts in command mode


30/40

vicommand mode

In command mode every charactertyped is acommand

You can move about in the buffer

Characters/lines can be deleted or moved

To enter text shift to insert mode


31/40

viinsert mode

In insert modecharacters typed are entered into thebuffer

Shift from command to insert move using:

i insert textbefore cursor a append text after cursor

Shift from insert back to command mode by typingESCape


32/40

vimoving around the file

Only part of the buffer is usually visible onscreen

In command mode can navigate through the file

Can choose to move: to a position within the buffer

to a position on the screen

to a particular text string


33/40

vipositioning the cursor

Examples:

H Go to top line on screen

L Go to last line on screen

M Go to middle line on screen h Move cursor left

j Move cursor down

k Move cursor up

l Move cursor right

Or you could use the arrow keys....


34/40

vimore movement

n Go to line n

/textCR Find text(forward search)

?textCR Find text(backward search)

n Find next occurrence of text(same direction)

N Find next occurrence of text(opposite direction)


35/40

vicomplex commands

Typing the :character in command mode causes aprompt to appear at the bottom of the screen

excommands can be typed here

:q

quit vi

will complain if there are unsaved changes

:q!orZZ quit and lose any unsaved changes


36/40

vireading and writing files

:rfilename

read the named file into the buffer

:w filename write the buffer to named file

:w

rewrite the buffer to an already named file


37/40

Useful Commands

Among the many Unix commands a few stand outas being particularly essential

These include

grep


38/40

Searching Files with grep

Thegrepcommand is actually a family

grep

All search files for strings which match specifiedpatterns

grep Failure *


39/40

More on grep

greps behaviour is modifiable via command lineoptions

-c display only count of matching

lines-i ignore casewhenmatching

-l display only names of files withmatching lines

-n display line numbers-v display only non-matching lines


40/40

The find Command Thefindcommand walks down a subtree of the file

system looking for files which match certaincreteria, such as:

wildcards file type (e.g. file, directory, special, link)

files owner

access time

modification time

wecome to unix

Documents