unix commands in a nutshell 2

8/6/2019 Unix Commands in a Nutshell 2

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Training Material


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Unix Commands in a Nutshell

Practical Usage of Commands

(Please open this PPT in openOffice.org)

DC/ SC/ Geo/Practice: Hi-Tech

Name of the project/support fn: Numonyx

Name of the author: Rohit ChopraDate Created:16-Jul-2009


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Objectives

Introduction

Unix Shell

Unix commands

Vi Editor

String Manipulation

Unix Utilities Monitoring Tools

Scheduling Jobs


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Flavors of UNIX

Mac OSXDarwin

Red HatLinux

SUNSolaris

HPHP-UX

DECDEC Ultrix

Zilog ComputersZeus

IBMIBM AIX

Microsofts UNIX operating system

to run on microcomputers

Xenix

Company

Product Name


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UNIXFeatures

Easier to modify the UNIX system code for installation on a new

computer rather than write from scratch a new operating system

Portability

Several users can use the same computer simultaneously

i.e. , more than one keyboard and terminal can be connectedto one computer

Highly cost-effective

Multi-user

Performing tasks simultaneously rather than sequentially

e.g., While printing a document , start editing another document

Each task is considered to be a process

Multitasking

DescriptionFeature


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File ManagementAnd SecurityNetworking

Services

Date and TimeServices

Input / Output

Services

SignalHandling

ProcessScheduling

SystemAdministrationand Accounting

MemoryManagement

UNIXUNIX

SYSTEMSYSTEM

KERNELKERNEL

UNIX Kernel


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Bourne Shell (sh)

C Shell (csh)

TC Shell (tcsh)

Korn Shell (ksh)

Bourne Again Shell (bash)

Different types of unix Shell


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Bourne Shell (sh)

This is the original UNIX shell

This shell doesnt have any interactive features.

C Shell (csh)

This shell provides C-like language for shell scripts.

All features of modern shell like command line history, alias are included in this shell

TC Shell (tcsh)

Similar to C shell but have emacs style editing

All features of modern shell are available.

Unix Shell


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Korn Shell (ksh)

This shell is now standard shell on UNIX systems

This shell provides all the features of C shell along with scripting similar to original Bourne shell (sh)

All features of modern shell are available.

Unix Shells

Bourne Again Shell (bash)

This is the first public domain shell

This shell is full implementation of IEEE Posix shell and tool specifications.

All features of modern shell like command line history, alias, command line editing etc are included in this shell.

Unix Shell


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- Ordinary Files

- Directory Files

- Special Files

- Standard Files

Classification of files in Unix


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A file can be addressed as container of data.

Directory is a container of files.

Every file is assigned to a Directory

$ls -ld /usr/bin

drwxr-xr-x 4 bin bin 17408 May 25 03:51 /usr/bin

$ls -ld /etc/passwd-rw-r--r-- 1 root security 6374 May 09 07:56 /etc/passwd$

Files and Directories


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* Used to reference Physical devices such as terminals and disks

* Read and written like ordinary files

Device Drivers associated with each file

$ls -ld /dev/nullcrw-rw-rw- 1 root system 2, 2 Aug 14 18:30 /dev/null$ls -ld /dev/cd0br--r--r-- 1 root system 14, 0 Oct 28 2005 /dev/cd0$ls -ld /dev/ttycrw-rw-rw- 1 root system 1, 0 Aug 14 18:29 /dev/tty$

Concept of Special Files


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Helps display information on the screen* Special Names for Communication channels

* Keyboard input channel is called Standard input

(stdin) - file id is 0

* Terminal Screen output is called Standard output

(stdout) - file id is 1

Diagnostic error messages (generated by a program) are sent to

Standard error

(stderr) - file id is 2 ( shown on terminal screen )

* All three files are open by default at the time oflogin

Concept of Standard Files


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* Hierarchical

* Ownership on each file

- User / Owner- Group- Others

* Separate security for permissions

- read- write and- execute

* Removable

* File Independence

* Time stamp on each file

- Modification time

- Access time

Features


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* Three levels of access

User/Owner, group, others

* Three types of access on Files and Directories

Read, Write, Execute

AccessM

ode Ordinary Directory

Read Examination of Listing ofFile Contents files within

Directory

Write Allows changing Creating new

of filecontents files withinDirectory

Execute Executing file as Searching thea command Directory allowed

allowed

Security and Access Methods


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Useful Commands

mkdir creates a new directory

rm removes a file

rmdir removes a directory

du displays disk usage

df displays number of free block

touch updates the time of last modification

find locates files that match certain area

file displays the type of file

pwd displays f ull pathname ofcurrent directory


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cat Concatenate & Print on screen or printer

$cat [Options] [Arguments]

Options - take input from stdin

-n no. of output lines

-s squeeze adj. blank lines

-v enable display of non-printing

characters-b used with -n to avoid numbering

blank lines

e.g.,

$cat try.c Display the contents of try.c on the screen

$cat Takes input from stdin i.e. keyboard and

displays on screen

File Contents


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Usages of cat command

$ cat f1 > f2 Takes input from file f1 & puts iton file f2

$ cat f2 > f3 f3 contains the contents off1

$ cat f4 >> f3 Appends the contents off4 to file f3

$ cat try[0-3] > final The file final contains contentsof try0, try1, try2 try3

$ cat test* > report The file report contains all filesbeginning with test


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UNIX Commands

$ Is -IList the files along with the protection bits and the user

$ Is -1 symtab.csymtab.otreegentest

$ Is -I-rw-rr 1 smj proj1 30766 Mar 3 15:08 symtab.c-rw-rr 1 smj proj1 8759 Mar 3 15:12 symtab.o

-rwxr-xr-x 4 smj proj1 40743 Mar 3 15:23 treegendrwxrwxr-x 1 smj proj1 53 Mar 1 09:15 test

$ Is -a List the files starting with .and ..also / hidden files....profile.cshrcsymtab.c

...

$ Is -iI 10936-rw-rrI smj proj1 3076 Mar 3 15:08 test.c10936 - inode number of file test.c


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Unix Command Continues...

wc WordCount$wc [Options] filename

Options - Display no. of lines, words, characters-I Display no. of lines-w Display no. of words

-c Display no. ofcharacterse.g., $ wc test.c

20 200 5678

20 - lines

200 - words

5678- characters


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cp copy a file

-i - user interactive mode

e.g.,$cp test.c test.c.baktest.c and test.c.bak contain the same contents

Extra disk storage

In Create link

e.g.,

$ ln first.c second.cThe file is referenced by two different namesNo Extra disk storage


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mv Moves or renames files and directories

-i interactive modee.g.,

$ mv old.c new.cRenames the file old.c as new.c

rm Deletes the indicated file(s) files

rm removes files and directories

-i remove interactively-f forcible remove

-r remove recursively Dangerous

used in conjunction with -i

touch Updates access, modification or change times of a file

-a update access time-m update modification time-c prevents creating the file

e.g., $ touch f1* The current system date & time stamp is put on the file f1* Iff1 does not exist then it is created with 0 bytes


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cmp Compare two files

If files are same no output is sent to the terminal, or else The line numberand the byte at which the first difference occurs is reported

-s Outputs nothing Registers return code

Return code

0 if files are identical1 if files are different2 on error

e.g.,

$ cmp test1 test2test1 and test2 differ in char 36 line 3$ cmp -s test1 test2$ echo $?

outputs 1 indicating that the files are different

File Comparison


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File Comparison continues..

diff - Reports more than one differences

$diff [Options] file1 file2

-b Ignores trailing blanks

-e Gives a list ofed commands so as to convert

file1 into file2.

e.g., $ diff test1 test2

Outputs: n1 a n3,n4

n1,n2 d n3

n1,n1 c n3,n4

where * n1 ,n2, n3 ,n4 are line numbers* a ,d, c means append, delete ,change respectively


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File Comparison continues..

commD

isplay common lines

$comm -[123] f1 f2Prints a three column output:

- lines that occur only in f1

- lines that occur only in f2

- lines that occur in both

comm -12 - prints lines common to the two filescomm -23 - prints only lines in the first file but not in the

second

comm -123 - prints nothing

e.g.,

$ comm test1 test2 Reports the common lines between

files test1, test2 and reports thelines differing

$ comm -12 test1 test2 Prints line common to both


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pack Compress the file

$ pack

e.g., $ pack try- Creates a file try.z which is packed

- Normally the hu

ge logs are packed- The size is reduced by 25 - 40 %

unpack Uncompress packed fileor

pcat

e.g., $ unpack try.zunpacks the file try.zor

$ pcat try.zread the contents of try.z

File Compression


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passwd To change the password or yourshell

chown To change the ownership of the file

$ chown owner filename

e.g., $ chown trg2 test.c* Initially the owner is trg1

* Only the owner or the superusercanchange the ownership of the file

File Security


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File Security Continues...

umask Set file creation mode mask$ umask nnn(nnn set file creation mode)umask can also be set as a shell variable

e.g.,

umask 022- Files normally created with 666 mode is assigned

644 permission

The value of each digit is subtracted from the corresponding "digit" specified bythe system for the creation of a file.


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tail Displays the last lines of fileoptions : -n (n= no. of lines)e.g., $ tail -30 test.cDisplays the last 30 lines of file test. c

head Displays the top lines of filee.g., $ head -10 test.c Displays the first 10 lines oftest.c

split S plits the file into different files as specified by the number of linese.g., $ split -20 test.c

Splits the file test.cin blocks of 20 lines and creates filesxaa,xaband so on, such that

xaa has first 20 lines oftest.cxab has the next 20 lines oftest.c

...

The file test.c is unaffected

$ split-20 test.c try Generates files as tryaa , tryab , tryac

paste Joins the two or more files horizontallye.g., $ paste xaa xabFile xaa and xab are joined horizontally and output to the terminal

File Operation


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The editor* Powerful full screen editor

* vi v/s ed, ex

* Mostly single key stroke commands

* Interface with ex

* Macro facility

* Ability to process text

Invoking $ vi filename

e.g., $ vi pgm.c

Modes :

* Command mode* Insert mode

* From Insert mode Pressing

remitts Command mode

The vi - Visual Editor


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Types of commands

* vi-commands (invisible)

Command mode

Commands can be categorised as :

* Cursor movement

* Text manipulations

- insert, delete, copy, change

* Marking/Selecting, Positioning* Search

Objects of interest recognized by vi:* characters

* words

* lines

* block


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Format of commands

[count] command [operand]

Use . to repeat last commandUse u to undo last command

CursorMovementLine Oriented :

^ or (zero) beginning of line$ end of line

Character orientedh move left

l move right

j move downk move up


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Format of commands (contd.)

Word Oriented :

e move to end of next word

w move to beginning of word

b move to beginning of previous word

E move to end of next word

ignoring punctuation

W move to beginning of word ignoring

punctuation

B move to previous word ignoring

punctuation


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Text Manipulation

Searching for a string :

/string for searching forward

?string for searching backward

Use n to continue search in the same direction

Use N to continue search in the opposite direction

s/oldstr/newstr commands can be used in vi


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Common Set commands

set ai Causes automatic indentation

set noai Nullifies the effect of auto-indent

set nu Causes line numbers to be displayed

set wrapmargin = n Sets n column right margin

set bf The beautify option Removes allunimportant control characters

set Causes a displays ofcurrent set options


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Shell Utilities and Commands


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Shell Startup Dot files

Helps in customizing UNIX System

* Executes .profile forbsh, ksh and bash when user logs on

* Executes .login and .cshrc for C Shell when user logs on

* Executes .logout for C Shell when user logs out from C-Shell

* Keeps track of the history mechanism In C Shell through the .history


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Shell Variables

User definedassignment : name = value

e.g., (on Bourne shell)

$ x=Hello how are you$ echo $x

Hello how are you

$ PATH=$PATH:/usr/games$ export PATH

$ echo $PATH

:.:/usr/bin:/bin:/usr/games:


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Predefined Special Parameters

$# number of positional parameters

$? exit value of last command

$$ process number of a process

$* all the parameters

$! process id of last command started with

asynchronous execution i.e., &


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Variables Used by Shell in .profile

HOME login dir

PATH search path forcommands

PS1 primary system prompt

PS2 secondary system prompt (eg. With whilestatements)

MAIL files containing mail messages

TERM terminal type


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To algebraically compare variable values

test $num1 -eq $num2

Other algebraic operators -ne, -gt -ge -lt, -le

File related

$ test -f file True if file exists and is an ordinary file

$ test -r file True if file exists and is readable file

$ test -w file True if file exists and is writable file

$ test -s file True if file exists and has size greater than zero


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grep get regular expressions only

fgrep fast, several simple strings at one time

egrep extended grep, can handle more powerfulexpressions like | - or operators

FILTERS :


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Searching Files with grep

e.g.,

$ grep -ni func1 *.c Prints all the lines and linenumbers in files *.c that match pattern func1

ignoring the case

$ grep * * Search for the pattern * in all the files

$ ls -l | grep ^d Searches for all subdirectories


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Cut

* Deletes columns from a file producing a new file with

shorter lines

* Cu

ts ou

t selected fields of ea

ch line in a file.

* Cuts columns from a table or fields from a file which can

be of type

- Fixed length fields or

- Delimited by some character

Processing Tabular Data


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Cut (contd.)

cut -c list { file1 file2 ...}e.g.,

cut -c 5-70 file1

cut would pass 5-70 characters from file1

cut -flist {-d char } {file1 file2....}

e.g.,

who | cut -d -f1

gives a list ofuser login names

cut -d: -f 1,5 /etc/passwd

gives a list ofuser ID and names


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PS, kill

$ somecommand &

5511 - pid

$ps

pid tty time command

3432 2 0 : 24 -sh5765 2 0 : 03 ps5511 2 0 : 51 somecommand

$ kill 5511$ ps

pid tty time command

3432 2 0 : 24 -sh5985 2 0 : 03 ps


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$ stubborn-cmd &

pid tty time command3432 2 0 : 24 -sh6004 2 0 : 03 ps5995 2 0 : 44 stubborn-cmd$ kill 5995

$ ps pid tty time command3432 2 0 : 24 -sh6004 2 0 : 03 ps5995 2 0 : 44 stubborn-cmd$ kill -9 5995

$ ps pid tty time command3432 2 0 : 24 -sh6103 2 0 : 03 ps


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1. Usercommunication commandsmailwritetalkpostnewsmesgwall

2. Networking commandsuucpuutorlogintelnet

ftprcpuuxsftpscp

Communication Features


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Practical Use of the Command (cat)

$cat /etc/passwd > temp

$sort < temp

$ rm temp

These statements first create a temporary file, Sort the file

and then delete the temporary file.This same result can be

achieved through a single unix statement.

$ cat /etc/passwd | sort

This requires No need ofcreation/deletion of a file and then sorts

the filepasswd as per the first entry in passwd.


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Practical Use of the Command (find)

find . -name text.xmlThis command will search a file text.xml from the

current path of the directory.

find / -atime -30 -print

This command will list all the files accessed less

30 days ago.

find / -atime +30 -print

This command will list all the files accessed after30 days


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find . -type f -print | xargs grep -il StringName

This is a very useful command which is a

combination of find and grep commands. This

command will find a file which contains a matching

StringName in it.

find /directory -mtime +30 -print -exec rm {} \;

This command will remove all the files in /directory that have

not been modified in 30 days.


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find $SEARCH_PATH -size +5000000c -print

To search for files greater than 5MB we can use the

above command where the + (plus sign) specifies greater than,

and the c denotes bytes

find $SEARCH_PATH -mtime 1 -print

This command will find all files that have been modified, or

created, in the last 24 hours

TS=$(date +%m%d%y%H%M%S)

This date command gives two digits for month, day, year,

hour, minute, and second:


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Practical Use of the Command (SED)

chsh username new_default_shell

The chsh command, short forchange shell, allows you to modifythe system environment for your login

SED is used to edit a large number ofconfiguration files .

for each in `ls *.cfg`; domv $each $each.bak #Safety First!sed '30,35s/^/\#/g' $each.bak > $eachdone

This will flow through all of the config files in a certain directory

and add a # sign at the beginning of lines 30 through 35,

commenting those lines out and if all goes

well, delete all of the .bak files created as backups by the script.


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Practical Use of the Command (AWK)

awk ' '{print $1}' file

This command is used to extract the first column from a file.AWK command allows the user to manipulate files that are

structured as columns of data and strings.

ls files_list| awk '{print "mv "$1" "$1".new"}' | shThis command will help in renaming the files (append .new

to "files_list"):

unix commands in a nutshell 2

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