#!/bin/bash
# A sample Bash script
echo Hello World!

#!/bin/bas
# the interpreter path is misspelled
echo Hello World!

$ ./badbang.sh
$ bash badbang.sh

$ ./badbang.sh
bash: ./badbang.sh: cannot execute: required file not found
$ bash badbang.sh
Hello World!

$ myvar = Hello
$ myvar=Hello
$ echo $myvar
$ echo $MYVAR

$ myvar = Hello
bash: myvar: command not found
$ myvar=Hello
$ echo $myvar
Hello
$ echo $MYVAR

#!/bin/bash
# A simple variable example
myvariable=Hello
anothervar=Linux
echo $myvariable $anothervar
echo
sampledir=/etc/apt
ls $sampledir

$ myvar=Hello World
$ myvar='Hello World'
$ echo $myvar
$ newvar="More $myvar"
$ echo $newvar
$ newvar='More $myvar'
$ echo $newvar

$ myvar=Hello World
bash: World: command not found
$ myvar='Hello World'
$ echo $myvar
Hello World
$ newvar="More $myvar"
$ echo $newvar
More Hello World
$ newvar='More $myvar'
$ echo $newvar
More $myvar

#!/bin/bash
# A simple copy script
cp $1 $2
# Let's verify the copy worked
echo Details for $2
ls -lh $2

$ ./mycopy.sh salesdata.txt backup.txt
Details for backup.txt
-rw-r--r-- 1 student student 123 Sep 25 12:11 backup.txt

#!/bin/bash
# special variables set by the system
echo "Script name: $0"
echo "Number of arguments: $#"
echo "All arguments: $@"
echo "Second argument: $2"
echo "User: $USER, host: $HOSTNAME"
echo "This is line $LINENO"

$ ./args.sh red green blue
Script name: ./args.sh
Number of arguments: 3
All arguments: red green blue
Second argument: green
User: student, host: ubuntu-lab
This is line 8

#!/bin/bash
# demonstrate variable scope 1.
var1=blah
var2=foo
# Let's verify their current value
echo $0 :: var1 : $var1, var2 : $var2
export var1
./script2.sh
# Let's see what they are now
echo $0 :: var1 : $var1, var2 : $var2

#!/bin/bash
# demonstrate variable scope 2
# Let's verify their current value
echo $0 :: var1 : $var1, var2 : $var2
# Let's change their values
var1=flop
var2=bleh

#!/bin/bash
# Ask the user for their city
echo Hello, which city are you from?
read varcity
echo It\'s nice to meet someone from $varcity

$ ./introduction.sh
Hello, which city are you from?
Mansoura
It's nice to meet someone from Mansoura

#!/bin/bash
# Ask the user for login details
read -p 'Username: ' uservar
read -sp 'Password: ' passvar
echo
echo Thank you $uservar, we now have your login details

$ ./login.sh
Username: student
Password: 
Thank you student, we now have your login details

#!/bin/bash
# A basic summary of my sales report
echo Here is a summary of the sales data:
echo ====================================
echo
cat /dev/stdin | cut -d' ' -f 2,3 | sort

$ cat salesdata.txt | ./summary.sh
Here is a summary of the sales data:
====================================

apples 20
oranges 5
peaches 7
watermelons 12

#!/bin/bash
# Basic arithmetic using let
let a=5+4
echo $a
let "a = 5 + 4"
echo $a
let a++
echo $a
let "a = 4 * 5"
echo $a
let "a = $1 + 30"
echo $a

$ ./let_example.sh 15
9
9
10
20
45

#!/bin/bash
# Basic arithmetic using expr
expr 5 + 4
expr "5 + 4"
expr 5+4
expr 5 \* $1
expr 11 % 2
a=$( expr 10 - 3 )
echo $a

$ ./expr_example.sh 12
9
5 + 4
5+4
60
1
7

#!/bin/bash
# Basic arithmetic using double parentheses
a=$(( 4 + 5 ));   echo $a
a=$((3+5));       echo $a
b=$(( a + 3 ));   echo $b
b=$(( $a + 4 ));  echo $b
(( b++ ));        echo $b
(( b += 3 ));     echo $b
a=$(( 4 * 5 ));   echo $a

$ ./expansion2.sh
9
8
11
12
13
16
20

$ echo $(( 7 / 2 )) $(( 7 % 2 ))
3 1
$ echo $(( 2 * 3 + 4 )) $(( 2 * (3 + 4) ))
10 14
$ a='Hello World'
$ echo ${#a}
11

#!/bin/bash
# Basic if statement
if [ $1 -gt 100 ]
then
    echo Hey that\'s a large number.
    pwd
fi
date

$ ./if_example.sh 15
Fri Sep 25 12:13:04 PM UTC 2026
$ ./if_example.sh 150
Hey that's a large number.
/home/student/lab11
Fri Sep 25 12:13:05 PM UTC 2026

$ test 001 = 1
$ echo $?
1
$ test 001 -eq 1
$ echo $?
0

$ touch myfile
$ test -s myfile
$ echo $?
1
$ ls /etc > myfile
$ test -s myfile
$ echo $?
0

#!/bin/bash
# elif statements
if [ $1 -ge 18 ]
then
    echo You may go to the party.
elif [ $2 == 'yes' ]
then
    echo You may go to the party but be back before midnight.
else
    echo You may not go to the party.
fi

$ ./if_elif.sh 20 no
$ ./if_elif.sh 16 yes
$ ./if_elif.sh 16 no

#!/bin/bash
# case example
case $1 in
    start) echo starting ;;
    stop) echo stopping ;;
    restart) echo restarting ;;
    *) echo don\'t know ;;
esac

$ ./case2.sh start
starting
$ ./case2.sh stop
stopping
$ ./case2.sh restart
restarting
$ ./case2.sh pause
don't know

#!/bin/bash
a=7
b=3
echo '$a + $b'
echo "$a + $b"
echo $(( a + b )) $(( a / b )) $(( a % b ))
expr $a \* $b
let "c = a * b - 1"
echo $c ${#c}

$ ./practice1.sh
$a + $b
7 + 3
10 2 1
21
20 2

$ test 5 -lt 12
$ echo $?
0
$ test abc = ABC
$ echo $?
1
$ test 010 -eq 10
$ echo $?
0

$ test 010 = 10
$ echo $?
1
$ test -z ""
$ echo $?
0
$ test -e nofile.txt
$ echo $?
1

#!/bin/bash
# print the larger of two numbers
if [ $1 -gt $2 ]
then
    echo "The larger number is $1"
elif [ $1 -lt $2 ]
then
    echo "The larger number is $2"
else
    echo "Both numbers are $1"
fi

$ ./larger.sh 17 42
The larger number is 42
$ ./larger.sh 42 17
The larger number is 42
$ ./larger.sh 9 9
Both numbers are 9

#!/bin/bash
# a shop bill with a discount
read -p "Price of one item: " price
read -p "Quantity: " qty
total=$(( price * qty ))
echo "Total: $total"
if [ $total -ge 500 ]
then
    discount=$(( total / 10 ))
    echo "Discount: $discount"
    echo "To pay: $(( total - discount ))"
else
    echo "No discount, to pay: $total"
fi

$ ./bill.sh
Price of one item: 120
Quantity: 3
Total: 360
No discount, to pay: 360
$ ./bill.sh
Price of one item: 200
Quantity: 3
Total: 600
Discount: 60
To pay: 540