Unix Training2

8/11/2019 Unix Training2

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UNIX Training

Unix is simple But it requires a genius to understand its

simplicity Dennis Ritchie

Compiled by

Ulagammal Paramasivam


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Unix Training

Basic Terminologies

Fundamentals of Unix OS

Basic Unix Commands (internaland external)

Filenames, Meta charactersUsing the vi Editor

Shell Scripting Overview (Typesof Shells)

Creating Shell ScriptsAdvanced Shell Scripting

Scheduling jobs in Unix


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Basic Terminologies

Unix WorkstationSingle user computer running Unix

MultitaskingCooperative MultitaskingProcesses voluntarily sharing theCPU

Preemptive MultitaskingOSforces the processes for the sharingof the CPU


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Basic Terminologies (contd)

KernelThe core of the Unix OS

Responsibilities of the KernelAddress space mapping

Current status of the process

Owner of the process

Execution priority of the process

Resource usage of the process


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Basic Terminologies (contd)

ShellUser interface to the kernel. It is thecommand processor

ProcessA running instance of any program

Process ID (PID)

Any process under Unix containsan address space and set of data.PID is a unique number thatidentifies a process in the Kernel


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Fundamentals of Unix

The different flavors of UnixSolaris - Sun Microsystems, HIXHPUnix, AIXAT & T Bell Laboratories

The four main blocks inUnix File System

Boot Block

Super Block

I-Node ListData Block


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Fundamentals of Unix (contd)

Super BlockKeeps track of the entire file system

Boot Block

Contains the code to bootstrapthe OS

I(nformation)-NodeList of Inodes and the info aboutdata blocks

Data BlockActual data


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File System


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Built-in Variables$HOMEThe Home directory of anuser

$PATHThe path can be

accessed using this$PS1Primary prompt

$PS2Secondary prompt

$SHELLType of shell being used

$$ - Current shells Process ID

$PPIDCurrent shells parentprocess ID

$PWDPrint current workingdirectory


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Home DirectoryThe default directory which isavailable when a user logs in.

To access the home use the$HOME built-in variable

Types of ShellscshC Shell

bshBourne ShellkshKorne Shell


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Using PathsAbsolute Path

Relative Path

Relationship of Kernel,Shells and Applications


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Filenames, Meta characters

These are special characters inUnix which are "wild card"characters; they can representother characters.

* - Represents zero or morecharacters? - Represents zero or onecharacterExamples:

ls f* - List all files starting with "f"

ls *.txt - List all files with ".txt" extension

grep word *.txt - Grep for "word" in allfiles having ".txt" extension


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Unix Commands

The shell does not start a new process toexecute the Internal Commandscd, pwd, read, exit, shift, set

The shell starts a new process to executeExternal Commandsls, cat, grep, find, cut, tr, uniq, sort,

diff, cal, more, tar, kill, wc, who, which,

sleep, touch, chmod, date, head, tail, tac,

id, hostname, passwd, stty, nohup, man, compress


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Unix Commands (contd)

cd - Change Directorycd # Takes to $HOME dircd

pwd - Print the current WorkingDirectory

read - Read an input from userread var1

exit - Exit from the current shellexit 0Indicates successNon-ZeroIndicates Failure


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shift - Shift one positional parameter in

command line

shift [n]

set - Set environmental variables

set -ax

ls - List the contents of a directory

Options:

-x - Widthwise

-l - Long listing-t - Time-wise

-r - Reverse Listing


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cat - Concatenate filecontents

cat []

grep - Search for patterns in afile

-i - Ignore case-l - Display filename-c - Count of occurrence-v - Negate match-n - Display with preceding line#

tr - Translate characterstr [option] pattern1 [pattern2]-s - Trim multiple spaces to singlespace-dDelete occurrence of pattern


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find - Find files in the current

directory and sub-directories

find name filename [options] [type ] {-ls |[-exec } {}\;]

options with -[ac]time:

+nMore than N days

-n - Less than N days

n - Exactly N days


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cut - Cut a portion of a file

cut [options] filename

Options:-c - Cut columns in file based on position

-d Extract fields using the

delimiter

-fCut fields based on the delimiterspecified. Default delimiter is


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sort - Sort the contents of a file

sort [options]

Options:

-uSort and write unique records

-fFold-case (Case insensitive)

-rReverse Sorting

-bIgnore leading blanks

-o - Create output file with the sorted

content


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uniq - Filter/ report uniq lines ofa file

uniq [options] filename

Displays the unique records in a file

Options:

-cCount of duplicate entries

-dDisplay distinct records [which are

duplicated]-uDisplay non-duplicate records

Pre-requisite: Input file must be sorted to

use uniq command


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diff - Find differencebetween two text files

diff cal - Display the calendarof an year

cal [[month] year]

more - Displays the filepage-wisemore


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tar - Tape Archive

tar [options] tar_filename

Options:

-cCreate tar file

-vVerbose

-fFile [Use the tar filename]

-xExtract

-tToC of tar file


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kill - Kill a Unix Processkill [-9] -9It is the sure kill command

wc - count the number ofwords, characters and lines in afile

wc [options] Options:-lReturn the number of lines in a

file-wReturn the number of words

in a file-c - Return the number of

characters in a file


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who - List the users currentlylogged in

who [am i]

am iThe current users infois displayed

which - Locate a commandwhich

sleep - Suspend execution for

n secondssleep


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touch - touch/ create a file

touch

chmod - Change the access

permissions on a filechmod

chmod [-R]

Permissions: 4Read, 2Write,

1Execute

ugoUser, Group and Others

+/- r, w, xRead, Write, Execute


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tacReverse the contents ofthe file

tac filename

date - Display the System

date, Time and Zonedate +%m/%d/%y

head - Display the first 10 linesof a file

head [-n] tail - Display the last 10 lines ofa file

tail [+/-n]


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id - Display the current users

IDentification

hostname - Display the hostname ofthe Unix system

passwd - Change the password for

the current user

stty - Set Terminal Type

stty erase ^H kill ^U


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nohup - No hang up

nohup

man - Manual pages for Unixcommands

man

compress - Compress the file

contents

compress


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Pipes, Redirection and Filters

Accomplish complex tasks bycombining Unix commands

RedirectionTransfer the output of acommand or content of a file toanother file or a command

Pipes - A form of redirection used inUnix that sends the output of one

program to another program forfurther processing. The symbol | isused for this


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Pipes, Redirection and Filters (contd)

Input and OutputRedirection:

Input RedirectionContents of a command arereceived as input to a file

Output RedirectionContents of a command are sentas output to a file


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Filtersawk and sed

awk - Aho, Weinberger and Kernighan

General purpose programming

language for text processing

sedStream Editor

Both the filters does not impact the

input files


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AWK ProgrammingStructure of AWK programs

pattern { action }

Examples:

print $1Displays the first field of the currentline

print $1, $3

Displays the first and third fields ofthe current line, separated by a

predefined string called the outputfield separator (OFS) whose defaultvalue is a single space character


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sedStream editor is used to perform basic texttransformations on an input stream. An e.g.:

$ cat pear.txt

jewel wormjewerly wormy worm jewelhay jewel jewel

kitten

$ cat pear.txt | sed -e "s/jewel/rock/"rock wormjewerly wormy worm rockhay rock jewelkitten

$ cat pear.txt | sed -e "s/e/WWW/g"jWWWwWWWl wormjWWWwWWWrly wormy worm jWWWwWWWlhay jWWWwWWWl jWWWwWWWlkittWWWn$


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The visual Editor

Using the "vi"sual EditorTwo modes of vi

Command ModeInsert Mode

Starting vivi filename edit a file named "filename"

Entering texti insert text left of cursorI insert text in line beginninga append text right of cursorA append text at end of line

Moving the cursorh left one spacej down one line

k up one linel right one space


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Using the "vi"sual Editor (contd)

Basic Editing

nx delete n characters

nX delete n characters before cursor

ndw delete n words forward

ndb delete n words backward

ndd delete n lines

D delete characters from cursor to end of line

nr replace n characters under cursor

ncw replace n words

C change text from cursor to end of line

o insert blank line below cursor

(ready for insertion)

O insert blank line above cursor

(ready for insertion)

nJ join n succeeding lines to current cursor line

u undo last change

U restore current line


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Moving around in a filenw forward word by word

nb backward word by word

$ to end of line

0 (zero) to beginning of line

- Goto previous line

+/ enter Goto next line

H to top line of screenM to middle line of screen

L to last line of screen

nG to line "n" of file

f scroll forward one screen

b scroll backward one screen

d scroll down one-half screen

u scroll up one-half screen

/ Search forward

? Search backward

n repeat last search in same direction

N repeat last search in opposite direction


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Closing and saving a file

ZZ save and quit

:wq Same as ZZ

:w save and resume

edit

:q Quit

:q! Quit discarding

changes


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Shell Scripting Overview

Types of ShellsBourne Shell: This is the original Unixshell written by Steve Bourne of BellLabs

C Shell: This shell was written at theUniversity of California, Berkeley. Itprovides a C-like language withwhich to write shell scripts andhence its name

Korn Shell: This shell was written by

David Korn of Bell labs. It is nowprovided as the standard shell onUnix systems. It is the most efficientshell.


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Shell Scripting Overview (contd)

Creating a Simple Shell ScriptTo list the users currently logged in:

who | cut -c1-8 | sort -u

vi disp_loggedusers

#!/bin/ksh

who | cut -c1-8 | sortu

:wq

$ chmod 755 disp_loggedusers

$ disp_loggedusers


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Shell Scripting Overview (contd)

Shell VariablesCreating Shell Variables

=value

No specific data types by default

No space before and after = signTo access the value use$

Example:

var1=Hi

var2=Krishnaecho $var1, $var2

Output:

Hi, Krishna


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Shell Scripting

Declare an integer variabletypeseti a_number=5

Declare an unsigned integertypesetui a_number=18

Declare variable to store lowercase

typesetl str1=HELLOecho $str1Output:hello

Declare variable to store uppercasetypesetu str1=hello

echo $str1Output:HELLO


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Shell Scripting

Sample shell to display theProcess ID Details

#!/bin/ksh

echo This shells process id: $$

echo This shells parent id: $PPIDexit 0

Finding the exit status of a shell

echo $?

Reading Inputs from User

read ,


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Shell Scripting

Decision Making and Control Flow

ifelse condition checking

Logical and Relational Operators

while loop

for loop

case construct

until commandBreaking the loop


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Shell Scripting

Decision Making andControl Flow (contd)

ifelse condition checking

if [ ]

then< true statements>

elif [ ]

then

else

fi


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Shell Scripting

Decision Making andControl Flow (contd)Logical Operators

-aAnd

-oOr!Not

Relational Operators==/ -eqEqual!=/ -neNot equal=/ -geGreater than or equal to>/ -gtGreater than


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Shell Scripting

Decision Making and ControlFlow (contd)

Looping constructs

while loop

while [ ]do

done

for loopfor in do

done


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Shell Scripting

Decision Making and ControlFlow (contd)

Looping constructsuntil loopuntil [ ]do

done

E.g.:i=0until [ $i -gt 4 ]do

i=`expr $i + 1`echo $i

done

1

23

4

5


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Shell Scripting


case construct

case $var in

opt1) statements;;break;;

opt2) statements;;

break;;

# Default option

*) default_statements;;

esac


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Shell Scripting


case construct

case $var in

opt1) statements;;break;;

opt2) statements;;

break;;

# Default option

*) default_statements;;

esac


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Shell Scripting

Breaking from the loopE.g.:

i=0

until [ $i -gt 4 ]

do

i=`expr $i + 1`

echo $i

break

done

Will produce the following output:

1


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crontabs and cronjobs

Restrictions: cron.allow and cron.deny

Crontab commands:

crontabl, -e

Crontab

E.g.:

30 18 * * * /home/user/t.ksh

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