Linux script
variables type
1)shell
2)system/environment
3) userdefine variable
Arithmetic calculation
Arithmetic Expansion ($((…)))
Using expr Command
Using let Command
!/bin/bash
echo “File Name: $0”
echo “First Parameter : $1”
echo “Second Parameter : $2”
echo “Quoted Values: $@”
echo “Quoted Values: $*”
echo “Total Number of Parameters : $#”
!/bin/sh
for TOKEN in $*
do
echo $TOKEN
done
echo $1
!/bin/bash
echo “Enter first number”
read x
echo “Enter second number”
read y
sum=$(( $x + $y ))
echo “The result of addition=$sum”
-eq Equality check
-ne Inequality check
-lt Less Than
-le Less Than or Equal
-gt Greater Than
-ge Greater Than or Equal
!/bin/sh
a=10
b=20
if [ $a == $b ]
then
echo “a is equal to b”
else
echo “a is not equal to b”
fi
!/bin/bash
echo “enter no”
read n
if [ $((n%2))==0 ]
then
echo “The number is even.”
else
echo “The number is odd.”
fi
!/bin/bash
if [ expr $a % 2 == 0 -a $a -gt 10 ]
then
echo “$a is even and greater than 10.”
else
echo “$a failed the test.”
fi
case EXPRESSION in
Pattern_Case_1)
STATEMENTS
;;
Pattern_Case_1)
STATEMENTS
;;
Pattern_Case_N)
STATEMENTS
;;
*)
STATEMENTS
;;
esac
filename:aa.sh
!/bin/bash
echo “enter your choice”
read mycase
case $mycase in
1) echo “You selected unix”;;
2) echo “You selected php”;;
3) echo “You selected java”;;
4) echo “You selected c++”;;
5) exit
esac
Save the script and make it executable.
$chmod +x aa.sh
$./aa.sh
!/bin/bash
echo “enter vowel”
read mycase
case $mycase in
‘a’) echo “vowel”;;
‘e’) echo “vowel”;;
‘i’) echo “vowel”;;
‘o’) echo “vowel”;;
‘u’) echo “vowel”;;
*) echo “consonent” ;;
esac
!/bin/bash
echo -n “Are you a student? [yes or no]: “
read response
case $response in
"Y" | "y" | "YES" | "Yes" | "yes")
echo -n "Yes, I am a student."
;;
"N" | "n" | "No" | "NO" | "no" | "nO")
echo -n "No, I am not a student.";
;;
*) echo -n "Invalid input"
;;esac
!/bin/bash
echo “Enter your lucky number”
read n
case $n in
101)
echo echo “You got 1stprize” ;;
510)
echo “You got 2nd prize” ;;
999)
echo “You got 3rd prize” ;;
*)
echo “Sorry,tryfor the next time” ;;
esac
!/bin/bash
for i in {1..5}
do
sleep $i &
done
echo “Background processes started…”
wait
echo “All processes have completed!”
~
test 5 -gt 2 && echo “Yes”
test 1 -lt 2 && echo “Yes”
for var in word1 word2 … wordN
do
Statement(s) to be executed for every word.
done
The C-style Bash for loop
for (( initializer; condition; step ))
do
shell_COMMANDS
done
/bin/bash
until
do
done
/bin/bash
while
do
done
display all the files starting with .bash and available in your home
!/bin/sh
for FILE in $HOME/.bash*
do
echo $FILE
done
!/bin/sh
for var in 0 1 2 3 4 5 6 7 8 9
do
echo $var
done
!/bin/bash
for (( i=1 ; i<=5 ; i++ ))
do
for (( j=1 ; j<=i ; j++ ))
do
echo -n “*”
done
echo ” “
done
!/bin/bash
for (( i=1 ; i<=5 ; i++ ))
do
for (( j=1 ; j<=i ; j++ ))
do
echo -n “$i”
done
echo ” “
done
!/bin/bash
for i in {1..5}
do
echo “Welcome $i times”
done
!/bin/bash
echo “Bash version ${BASH_VERSION}…”
for i in {0..10..2} #{START..END..INCREMENT}
do
echo “Welcome $i times”
done
Write a shell script that calculates the sum of integers from 1 to N using a loop.
!/bin/bash
echo “Enter a number (N):”
read N
sum=0
for (( i=1; i<=$N; i++ )); do
sum=$((sum + i))
done
echo “Sum of integers from 1 to $N is: $sum”
Create a script that searches for a specific word in a file and counts its occurrences.
!/bin/bash
echo “Enter the word to search for:”
read target_word
echo “Enter the filename:”
read filename
count=$(grep -o -w “$target_word” “$filename” | wc -l)
echo “The word ‘$target_word’ appears $count times in ‘$filename’.”
Create a script that checks for and removes duplicate lines in a text file.
!/bin/bash
input_file=”in.txt”
output_file=”output.txt”
sort “$input_file” | uniq > “$output_file”
echo “Duplicate lines removed successfully.”
Write a script that generates a secure random password.
!/bin/bash
Function to generate a random password
generate_password()
{
tr -dc ‘A-Za-z0-9!@#$%^&*()_+{}[]’ < /dev/urandom | fold -w 12 | head -n 1
}
Call the function and store the generated password
password=$(generate_password)
echo “Generated password: $password”
Create a shell script that finds and lists all empty files in a directory.
!/bin/bash
directory=”$1″
if [ -z “$directory” ]; then
echo “Usage: $0 “
exit 1
fi
if [ ! -d “$directory” ]; then
echo “Error: ‘$directory’ is not a valid directory.”
exit 1
fi
echo “Empty files in $directory:”
find “$directory” -type f -empty
Create a script that checks if a network host is reachable.
!/bin/bash
host=”$1″
if [ -z “$host” ]; then
echo “Usage: $0 “
exit 1
fi
ping -c 4 “$host”
if [ $? -eq 0 ]; then
echo “$host is reachable.”
else
echo “$host is not reachable.”
fi
/bin/bash
a=0
-gt is greater than operator
Iterate the loop until a is greater than 10
until [ $a -gt 10 ]
do
# Print the values
echo $a
# increment the value
a=`expr $a + 1`done
//was multiplication table
!/bin/bash
echo “Enter a Number”
read n
i=1
while [ $i -le 10 ]
do
echo ” $n x $i = $(( n * i ))”
i=$(( i + 1 ))
done
!/bin/bash
rows=5
for((i=rows; i>=1; i–))
do
for((j=1; j<=i; j++))
do
echo -n “* “
done
echo
done
!/bin/bash
clear
p=$1
r=$2
n=$3
let int=expr $p \* $r \* $n
int=expr $int / 100
echo “simple interest , $int”
!/bin/bash
echo “enter the year”
read a
year= $a
a=$(( $a %4 ))
if [ $a -eq 0 ];
then
echo “$year is leap”
else
echo “$year is not a leap year”
fi
!/bin/bash
echo “Enter any number”
read n
if [[ ( $n -eq 15 || $n -eq 45 ) ]]
then
echo “You won the game”
else
echo “You lost the game”
fi
!/bin/bash
echo “Enter your lucky number”
read n
if [ $n -eq 101 ];
then
echo “You got 1st prize”
elif [ $n -eq 510 ];
then
echo “You got 2nd prize”
elif [ $n -eq 999 ];
then
echo “You got 3rd prize”
else
echo “Sorry, try for the next time”
fi
========================================
!/bin/bash
echo “enter file name”
read fname
if [ -f $fname ]; then
echo “$fname file exist”
else
echo “sorry, $fname file does not exist”
fi
!/bin/bash
function F1()
{
echo ‘I like bash programming’
}
F1
!/bin/bash
echo “Enter directory name”
read ndir
if [ -d “$ndir” ]
then
echo “Directory exist”
elsemkdir $ndir
echo “Directory created”
fi
Creating Functions
function_name ()
{
list of commands
}
!/bin/sh
Define your function here
Hello ()
{
echo “Hello World”
}
Invoke your function
Hello
!/bin/sh
Define your function here
Hello ()
{
echo “Hello World $1 $2”
}
Invoke your function
Hello Zara Ali
!/bin/sh
Define your function here
Hello () {
echo “Hello World $1 $2”
return 10
}
Invoke your function
Hello Zara Ali
Capture value returnd by last command
ret=$?
echo “Return value is $ret”
!/bin/sh
Calling one function from another
number_one ()
{
echo “This is the first function speaking…”
number_two
}
number_two ()
{
echo “This is now the second function speaking…”
}
Calling function one.
number_one
!/bin/bash
echo -n “Enter Left-End: “
read le
echo -n “Enter Right-End: “
read ri
is_prime()
{
if [ $1 -lt 2 ]; then
return
fi
ctr=0
for((i=2;i<$1;i++))
{
if [ $(( $1 % i )) -eq 0 ]; then
ctr=$(( ctr +1 ))
fi
}
if [ $ctr -eq 0 ]; then
printf “%d ” “$1”
fi
}
printf “Prime Numbers between %d and %d are: ” “$le” “$ri”
for((i=le;i<=ri;i++))
{
is_prime $i
}
printf “\n”
!/bin/bash
is_odd()
{
x=$1
if [ $((x%2)) == 0 ]; then
echo “Invalid Input”
exit 1
else
echo “Number is Odd”
fi
}
is_odd 64
!/bin/bash
add()
{
return $(($1+$2))
}
multiply()
{
return $(($1*$2))
}
Call Addition for 3 and 4 == 7
add 3 4
Call multiplication for 3 and 4 == 12
multiply 3 4
Call Addition for 5 and 4 == 9
add 5 4
Store answer (always stores final function call returned value)
ans=$?
echo “$ans”
!/bin/bash
Name – math.sh
Purpose – Demo return value
————————————
user define function
math()
{
local a=$1
local b=$2
local sum=$(( a + b))
return $sum
}
call the math function with 5 and 10 as arguments
math 5 10
display back result (returned value) using $?
echo “5 + 10 = $?”
Test for empty arguments: Use the -z operator to check if an argument is empty
!/bin/bash
function check_empty()
{
if [ -z “$1” ]; then
echo “Error: Argument is empty!”
return 1
fi
echo “Argument: $1”
}
check_empty “apple”
check_empty “”
The following is one such function used to calculate the average of the given numbers.
!/bin/bash
find_avg()
{
len=$#
sum=0
for x in “$@”
do
sum=$((sum + x))
done
avg=$((sum/len))
return $avg
}
find_avg 30 40 50 60
printf “%f” “$?”
printf “\n”
Below function creates a simple digital clock on terminal
T Displays the 24-hour clock (00-23) in the format equivalent to HH:MM:SS
!/bin/bash
function digital_clock
{
clear
while [ 1 ]
do
date +’%T’
sleep 1
clear
done
}
digital_clock
This is the second function
!/bin/bash
compare()
{
file1 = $1
file2 = $2
cmp $file1 $file2
if [ $file1 -eq $file2 ]
then
echo “comparison is possible”
else
echo “compariosn is not possible”
fi
}
which nano
undo -> mu ->alt->u
clear alt->t
copy ctrl+shift+c
paste ctrl+shift+v