UNIX+Shell Scripting+Basics

8/6/2019 UNIX+Shell Scripting+Basics

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Shell

UNIX


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Agenda

Shell

bash

Shell Environment Shell Programming


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WhatWhat is a shell?WhatWhat is a shell?

Interactive UserInterface with anoperating system


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Types of Shell

The Bourne Shell ( /bin/sh)


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Types of Shell

The C Shell ( /bin/csh)


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Types of Shell

The Bourne Again Shell ( /bin/bash)


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How Shell Works?

INPUT

shell

OUTPUT ERROR


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So, Shell is any program that cantake input and interacts with OS


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Shell Basics

FilePathAbsolute Path (/etc/X11/xserver/SecurityPolicy)

Relative Path (../../file_name)


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Basics

Special Symbols ~ ( home Directory)

. ( current Directory) .. ( parent Directory)

` ( back tick )


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Basics

Redirections(,>>) Input Redirection

Output Redirection


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Basics

Input Redirection cat < /etc/resolv.conf

Input Piping echo I Love Unix | wc -w


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Basics

Error Redirection $ls -l /etc/not_existing_file

ls: /etc/reslo.conf: No such file or directory $ls -l /etc/not_existing_file 2> error.log

$cat error.log

ls: /etc/reslo.conf: No such file or directory


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Basics

Output & Error Redirection $ ls -ld /etc/resolv.conf /etc/noname &> output.txt

$echo output.txt ls: /etc/noname: No such file or directory

-rw-r--r-- 1 root root 50 2009-04-12 09:59/etc/resolv.conf


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Basics

The backtick (`)

allows to assign output of a shell

command to a variable.

$testing=`date`

$echo testing

Mon Apr 20 15:07:51 BDT 2009


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Environment Variables

Local Variable

Global Variable$ set | moreBASH=/bin/bashBASH_ARGC=()BASH_ARGV=()BASH_COMPLETION=/etc/bash_completionBASH_COMPLETION_DIR=/etc/bash_completion.dBASH_LINENO=()

BASH_SOURCE=()BASH_VERSINFO=([0]="3" [1]="2" [2]="13" [3]="1" [4]="release" [5]="i486-pc-linux-gnu")BASH_VERSION='3.2.13(1)-release'.......


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Setting & Unsetting EnvironmentVariables

$$test=testingtest=testing$$echo $testecho $testtestingtesting$$unset $testunset $test

$$echo $testecho $test


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Creating Global Variable

$test=it is not global variable$/bin/bash$echo $test

$test=it is global$export test$/bin/bash$echo $testit is global


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What is a Shell Script? A Text File

#hello.sh

echo hello, world

Running the Script

$chmod +x hello.sh$./hello.shhello, world


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Exit Status

$?

0 is True

% ls /does/not/exist

% echo $?

1

% echo $?

0


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Exit Status: exit

% cat > test.sh


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Logic: test

% test 1 -lt 10

% echo $?

0% test 1 == 10

% echo $?

1


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Logic: test

test

[ ]

[ 1 lt 10 ] [[ ]]

[[ thisstring =~ this ]]

(( )) (( 1 < 10 ))


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Logic: test

[ -f /etc/passwd ]

[ ! f /etc/passwd ]

[ -f /etc/passwd a f /etc/shadow ]

[ -f /etc/passwd o f /etc/shadow ]


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An aside: $(( )) for Math

% echo $(( 1 + 2 ))

3

% echo $(( 2 * 3 ))6

% echo $(( 1 / 3 ))

0


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Logic: if

if something

then

:

# elif a contraction of else if:

elif something-elsethen

:

else

then:

fi


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Logic: if

if [ $USER eq borwicjh ]

then

:

# elif a contraction of else if:elif ls /etc/oratab

then

:

else

then

:

fi


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Logic: if

# see if a file exists

if [ -e /etc/passwd ]

thenecho /etc/passwd exists

else

echo /etc/passwd not found!fi


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Logic: for

for i in 1 2 3

do

echo $idone


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Logic: for

for i in /*

do

echo Listing $i:ls -l $i

done


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Logic: for

for i in /*

do


done


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Logic: for

for i in /*

do


done


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Logic: C-style for

for (( expr1 ;

expr2 ;expr3 ))

do

listdone


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Logic: C-style for

LIMIT=10

for (( a=1 ;

a


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Logic: while

while something

do:

done


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Logic: while

a=0; LIMIT=10

while [ "$a" -lt "$LIMIT" ]

doecho -n "$a

a=$(( a + 1 ))

done


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Counters

COUNTER=0

while [ -e $FILE.COUNTER ]

doCOUNTER=$(( COUNTER + 1))

done


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Running Programs


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Searching: grep

% grep rayra /etc/passwd

% grep r rayra /etc

% grep r RAYRA /etc% grep ri RAYRA /etc

% grep rli rayra /etc


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Searching: find

% find /home/cention

-name *.lis

[all files matching *.lis]% find /home/cention

-mtime -1 name *.lis

[*.lis, if modified within 24h]% man find


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Searching: locate

% locate .lis

[files with .lis in path]

% locate log[also finds /var/log/messages]


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Make Your Life Easier

TAB completion

Control+R

history cd -

Study a UNIX Editor


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pushd/popd

% cd /tmp

% pushd /var/log

/var/log /tmp

% cd ..

% pwd

/var

% popd

/tmp


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Monitoring processes

ps

ps ef

ps u oracle ps Csshd

man ps


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Passing Arguments

% cat > test.sh


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Scheduling Jobs

% crontab -l

00 * * * daily-midnight-job.sh

0 * * * * hourly-job.sh* * * * * every-minute.sh

01 * * 01AM-on-sunday.sh

% EDITOR=vi crontab e% man 5 crontab


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UNIX+Shell Scripting+Basics

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