Scripting Symphony: A Shell Script Cheat Sheet

In my previous post I had explained about Shell scripting —

Unleashing the Power of Shell Scripting

In this blog let’s learn how to create shell scripts.

01_basic.sh

echo "Hello Guys!"

Output:-

Hello Guys!

02_comments.sh 

echo "Checking Comments"

#This is a single line comment

#comment
#This
#is
#multi-line
#comment

Output:-

echo "Checking Comments"

#This is a single line comment

<<com
This
is
multi-line
com

03_vardemo.sh
 
#Script to show how to use variables

a=10
name="Dhanush"
age=22

echo "My name is $name and age is $age"

name="Dhanu"
echo "My name is $name"

#Variable to store the output of a command
HOSTNAME=$(hostname)
echo "Name of this machine is $HOSTNAME"

Output:-

My name is Dhanush and age is 22
My name is Dhanu
Name of this machine is modus

04_constant_var.sh

#Constant variable
readonly COLLEGE="VTU"

echo "My college name is $COLLEGE"

Output:-

My college name is VTU

05_ui.sh

read -p "What is your name? " name
echo "Your name is $name"

Output:-

What is your name? Dhanush
Your name is Dhanush

06_strings.sh 

myVar="Hey Buddy, how are you?"

myVarLength=${#myVar}
echo "Length of the myVar is $myVarLength"

echo "Upper case is ${myVar^^}"

echo "Lower case is ${myVar,,}"

#To replace a string
newVar=${myVar/Buddy/1421}
echo "New Var is ---- $newVar"

#To slice a string
echo "After slice ${myVar:4:5}"

Output:-

Length of the myVar is 23
Upper case is HEY BUDDY, HOW ARE YOU?
Lower case is hey buddy, how are you?
New Var is ---- Hey 1421, how are you?
After slice Buddy

07_arithmetic.ksh

#Maths Calculation
x=10
y=2

let sum=$x+$y
echo "$sum"

echo "Subtraction is $(($x-$y))"

echo "Multiplication is $(($x*$y))"

Output:-

12
Subtraction is 8
Multiplication is 20

08_array.sh

#Array

myArray=( 0 1 20.5 Hello "Hello Guys" )
echo "All the values in the array are ${myArray[*]}"

echo "Value of 3rd index is  ${myArray[3]}"

#How to find no. of values in an array
echo "Length of an array is ${#myArray[*]}"

#Updating our array with new values
myArray+=( New 30 40 )

echo "Values of new array are ${myArray[*]}"

Output:-

All the values in the array are 0 1 20.5 Hello
Value of 3rd index is  Hello Hello Guys
Length of an array is 4
Values of new array are 0 1 20.5 Hello New 30 40

09_if_else.sh

read -p "Enter your marks:" marks

if [ $marks -gt 40 ]
then
        echo "You have Passed"
else
        echo "You have Failed!"
fi

Output:-

Enter your marks:80
You have Passed

Enter your marks:30
You have Failed!

10_elif.sh

read -p "Enter your marks: " marks

if [ $marks -ge 80 ]
then
        echo "Distinction"
elif [ $marks -ge 60 ]
then
        echo "First Class"
elif [ $marks -ge 40 ]
then
        echo "Second Class"
else
        echo "You have Failed!"
fi

Output:-

Enter your marks: 80
Distinction

Enter your marks: 60
First Class

Enter your marks: 40
Second Class

Enter your marks: 20
You have Failed!

11_loops.sh

#Shorter and preferred version

for i in {2..20..2}
do 
  echo "Table of 2 : $i"
done

Output:-

Table of 2 : 2
Table of 2 : 4
Table of 2 : 6
Table of 2 : 8
Table of 2 : 10
Table of 2 : 12
Table of 2 : 14
Table of 2 : 16
Table of 2 : 18
Table of 2 : 20

#Lengthy version

for i in 1 2 3 4 5 6 7 8 9 10
do
        echo "Number is $i"
done

Output:-

Number is 1
Number is 2
Number is 3
Number is 4
Number is 5
Number is 6
Number is 7
Number is 8
Number is 9
Number is 10

#Shorter version

for i in {2..20..2}
do 
  echo "Table of 2 : $i"
done

Output:-

Table of 2 : 2
Table of 2 : 4
Table of 2 : 6
Table of 2 : 8
Table of 2 : 10
Table of 2 : 12
Table of 2 : 14
Table of 2 : 16
Table of 2 : 18
Table of 2 : 20

#Normal version

for (( i=10; i>=1; i-- ))
do
  echo "Number is $i"
done

Output:-

Number is 1
Number is 2
Number is 3
Number is 4
Number is 5
Number is 6
Number is 7
Number is 8
Number is 9
Number is 10

12_for_file.sh (read names for .txt file)

#Getting values from a file names.txt

FILE="/users/mod1421/1421/names.txt"

for name in $(cat $FILE)
do
        echo "Name is $name"
done

Output:-

Name is ChristopherNolan
Name is Yash
Name is DulquerSalmaan
Name is PrithvirajSukumaran
Name is ShahrukhKhan

13_while.sh

count=0
num=10

while [[ $count -le $num ]]
do
        echo "Value of count var is $count"
        let count++
done

Output:-

Value of count var is 0
Value of count var is 1
Value of count var is 2
Value of count var is 3
Value of count var is 4
Value of count var is 5
Value of count var is 6
Value of count var is 7
Value of count var is 8
Value of count var is 9
Value of count var is 10

14_for_with_array.sh

myArray=(1 2 3 HELLO Hi )

length=${#myArray[*]}

for(( i=0;i<length;i++ ))
do
        echo "Value of array is ${myArray[$i]}"
done

Output:-

Value of array is 1
Value of array is 2
Value of array is 3
Value of array is HELLO
Value of array is Hi

15_while_with_file.sh

while IFS="," read  id name age
do
        echo "Id is $id"
        echo "Name is $name"
        echo "Age is $age"
done < test.csv

Output:-

Id is id
Name is name
Age is age
Id is 01
Name is dhanush
Age is 22
Id is 02
Name is sonu
Age is 24
Id is 03
Name is bunty
Age is 24

16_case.sh

echo "Choose an option"
echo "a to print date"
echo "b to print list of scripts"
echo "c to check the current location"

read choice

case $choice in
        a)
                echo "Today's date is:"
                date
                echo "Ending..."
                ;;
        b)ls;;
        c)pwd;;
        *)echo "Please choose a valid option"
esac

Output:-

Choose an option
a to print date
b to print list of scripts
c to check the current location
a
Today's date is:
Fri Dec  8 18:35:29 GMT 2023
Ending...

Choose an option
a to print date
b to print list of scripts
c to check the current location
b
01_basic.ksh              06_array.ksh              11_case.ksh               16_while.ksh              21_function_demo.ksh      26_continue.sh
02_comments.ksh           07_strings.ksh            12_logical.ksh            17_until.ksh              22_function_with_arg.ksh  27_redirect.sh
03_vardemo.ksh            08_arithmetic.ksh         13_ternary.ksh            18_infinite.ksh           23_args.sh                names.txt
04_constant_var.ksh       09_if_else.ksh            14_loops.ksh              19_for_with_array.ksh     24_shift_args.sh          redirect.log
05_ui.ksh                 10_elif.ksh               15_for_file.ksh           20_while_with_file.ksh    25_break.sh               test.csv
Choose an option
a to print date
b to print list of scripts
c to check the current location
c

Choose an option
a to print date
b to print list of scripts
c to check the current location
d
Please choose a valid option

17_logical.sh

#AND OPERATOR

read -p "What is your age? " age
read -p "Your country: " country
if [[ $age -ge 18 ]] && [[ $country -eq "India" ]]
then
        echo "You can vote"
else
        echo "You can't vote"
fi

Output:-

What is your age? 22
Your country: India
You can vote

OR

What is your age? 16
Your country: USA
You can't vote

18_ternary.sh

#cond1 && cond2 || cond3

read -p "Enter your age:" age
[[ $age -ge 18 ]] && echo "Adult" || echo "Minor"

Output:-

Enter your age:22
Adult

OR

Enter your age:16
Minor

19_until.sh  

a=0

until [ $a -eq 9 ]
do
        echo "Value of a is $a"
        let a++
done

Output:-

Value of a is 0
Value of a is 1
Value of a is 2
Value of a is 3
Value of a is 4
Value of a is 5
Value of a is 6
Value of a is 7
Value of a is 8

20_infinite.sh (infinite loop with interval)

#Infinite loop

for (( ;; ))
do
        echo "Hi buddy"
        sleep 2
done

Output:-

Hi buddy
Hi buddy
Hi buddy
Hi buddy

21_break.sh

#Example of break in a loop
#We just have to confirm if a given no. is presnt or not

no=6

for i in 1 2 3 4 5 6 7 8 9 10
do
if [ $no -eq 6 ]
then
echo "$no is found!!!"
break
fi
echo "Number is $i"
done

Output:-

6 is found!!!

22_continue.sh

#Example of continue in a loop
#To print odd numbers

for i in 1 2 3 4 5 6 7 8 9 10
do
r=$((i%2))
if [ $r -q 0 ]
then
continue
fi
echo "Odd numbers is $i"
done
 
Output:-

Odd numbers is 1
Odd numbers is 3
Odd numbers is 5
Odd numbers is 7
Odd numbers is 9

23_function_demo.sh

#To create function
welcomenote () {
echo "------------------------"
echo "Welcome"
echo "------------------------"
}

#To call function
welcomenote
welcomenote

Output:-
------------------------
Welcome
------------------------
------------------------
Welcome
------------------------

24_function_with_arg.sh

welcomenote () {
        echo "-----------"
        echo "Welcome $1"
        echo "Age is $2"
        echo "-----------"
}

welcomenote Dhanush 22
welcomenote Chandra 24
welcomenote Sonu 24

Output:-
-----------
Welcome Dhanush
Age is 22
-----------
-----------
Welcome Sonu
Age is 24
-----------
-----------
Welcome Bunty
Age is 24
-----------

25_args.sh 

#To access the arguments

if [ $# -eq 0 ]
then
   echo "Please enter an argument" 
        exit 1
fi

echo "First argument is $1"
echo "Second argument is $2"

echo "All the arguments are - $@"
echo "Number of arguments are - $#"

Output:-

./25_args.sh dhanush 1421 is empid 

Please enter an argument

OR

First argument is dhanush
Second argument is 1421
All the arguments are - dhanush 1421 is empid sample.txt
Number of arguments are - 4

26_shift_args.sh

#To create a user, provide username and description

echo "Creating user"
echo "Username is $1"

shift
echo "Description is $@"

Output:-

Creating user
Username is Dhanush
Description is 1421 is empid

27_redirect.sh

echo "List of all files in my directory-1421 are: $(ls -lt)" > redirect.log

Output:- (vi redirect.log)

List of all files in my directory-1421 are: total 240
-rw-r--r--    1 mod1421  dba            2176 Dec 08 15:37 redirect.log
-rwxrwxr-x    1 mod1421  dba              77 Dec 08 15:35 27_redirect.sh
-rw-rw-r--    1 mod1421  dba             160 Dec 08 14:59 26_continue.sh
-rw-rw-r--    1 mod1421  dba             204 Dec 08 14:56 25_break.sh
-rw-rw-r--    1 mod1421  dba             130 Dec 08 14:53 24_shift_args.sh
-rw-rw-r--    1 mod1421  dba             296 Dec 08 14:48 23_args.sh
-rwxrwxr-x    1 mod1421  dba             285 Dec 08 13:03 11_case.ksh
-rwxrwxr-x    1 mod1421  dba             131 Dec 08 12:22 09_if_else.ksh
-rwxrwxr-x    1 mod1421  dba             265 Dec 08 11:18 22_function_with_arg.ksh
-rwxrwxr-x    1 mod1421  dba             116 Dec 08 11:08 16_while.ksh
-rwxrwxr-x    1 mod1421  dba             162 Dec 08 11:05 21_function_demo.ksh
-rwxrwxr-x    1 mod1421  dba             125 Dec 08 10:48 20_while_with_file.ksh
-rw-rw-r--    1 mod1421  dba             103 Dec 08 10:45 test.csv
-rwxrwxr-x    1 mod1421  dba              76 Dec 07 19:02 18_infinite.ksh
-rwxrwxr-x    1 mod1421  dba             336 Dec 07 18:58 06_array.ksh
-rwxrwxr-x    1 mod1421  dba             138 Dec 07 18:34 19_for_with_array.ksh
-rwxrwxr-x    1 mod1421  dba              80 Dec 07 18:16 17_until.ksh
-rwxrwxr-x    1 mod1421  dba             145 Dec 07 17:23 15_for_file.ksh
-rw-rw-r--    1 mod1421  dba              71 Dec 07 13:22 names.txt
-rwxrwxr-x    1 mod1421  dba              74 Dec 07 13:15 14_loops.ksh
-rwxrwxr-x    1 mod1421  dba             120 Dec 07 12:58 13_ternary.ksh
-rwxrwxr-x    1 mod1421  dba             207 Dec 07 12:53 12_logical.ksh
-rwxrwxr-x    1 mod1421  dba             231 Dec 07 12:22 10_elif.ksh
-rwxrwxr-x    1 mod1421  dba             139 Dec 07 11:55 08_arithmetic.ksh
-rwxrwxr-x    1 mod1421  dba              74 Dec 07 11:45 05_ui.ksh
-rwxrwxr-x    1 mod1421  dba             309 Dec 07 11:37 07_strings.ksh
-rw-rw-r--    1 mod1421  dba             110 Dec 07 11:01 02_comments.ksh
-rwxrwxr-x    1 mod1421  dba              32 Dec 07 10:48 01_basic.ksh
-rw-rw-r--    1 mod1421  dba              91 Dec 06 12:10 04_constant_var.ksh
-rw-rw-r--    1 mod1421  dba             263 Dec 06 12:07 03_vardemo.ksh

crontab -e

0 16 8 12 05  cd /users/mod1421/1421 && ./27_redirect.sh

Output:-

List of all files in my directory-1421 are: total 240
-rw-r--r--    1 mod1421  dba            2176 Dec 08 15:37 redirect.log
-rwxrwxr-x    1 mod1421  dba              77 Dec 08 15:35 27_redirect.sh
-rw-rw-r--    1 mod1421  dba             160 Dec 08 14:59 26_continue.sh
-rw-rw-r--    1 mod1421  dba             204 Dec 08 14:56 25_break.sh
-rw-rw-r--    1 mod1421  dba             130 Dec 08 14:53 24_shift_args.sh
-rw-rw-r--    1 mod1421  dba             296 Dec 08 14:48 23_args.sh
-rwxrwxr-x    1 mod1421  dba             285 Dec 08 13:03 11_case.ksh
-rwxrwxr-x    1 mod1421  dba             131 Dec 08 12:22 09_if_else.ksh
-rwxrwxr-x    1 mod1421  dba             265 Dec 08 11:18 22_function_with_arg.ksh
-rwxrwxr-x    1 mod1421  dba             116 Dec 08 11:08 16_while.ksh
-rwxrwxr-x    1 mod1421  dba             162 Dec 08 11:05 21_function_demo.ksh
-rwxrwxr-x    1 mod1421  dba             125 Dec 08 10:48 20_while_with_file.ksh
-rw-rw-r--    1 mod1421  dba             103 Dec 08 10:45 test.csv
-rwxrwxr-x    1 mod1421  dba              76 Dec 07 19:02 18_infinite.ksh
-rwxrwxr-x    1 mod1421  dba             336 Dec 07 18:58 06_array.ksh
-rwxrwxr-x    1 mod1421  dba             138 Dec 07 18:34 19_for_with_array.ksh
-rwxrwxr-x    1 mod1421  dba              80 Dec 07 18:16 17_until.ksh
-rwxrwxr-x    1 mod1421  dba             145 Dec 07 17:23 15_for_file.ksh
-rw-rw-r--    1 mod1421  dba              71 Dec 07 13:22 names.txt
-rwxrwxr-x    1 mod1421  dba              74 Dec 07 13:15 14_loops.ksh
-rwxrwxr-x    1 mod1421  dba             120 Dec 07 12:58 13_ternary.ksh
-rwxrwxr-x    1 mod1421  dba             207 Dec 07 12:53 12_logical.ksh
-rwxrwxr-x    1 mod1421  dba             231 Dec 07 12:22 10_elif.ksh
-rwxrwxr-x    1 mod1421  dba             139 Dec 07 11:55 08_arithmetic.ksh
-rwxrwxr-x    1 mod1421  dba              74 Dec 07 11:45 05_ui.ksh
-rwxrwxr-x    1 mod1421  dba             309 Dec 07 11:37 07_strings.ksh
-rw-rw-r--    1 mod1421  dba             110 Dec 07 11:01 02_comments.ksh
-rwxrwxr-x    1 mod1421  dba              32 Dec 07 10:48 01_basic.ksh
-rw-rw-r--    1 mod1421  dba              91 Dec 06 12:10 04_constant_var.ksh
-rw-rw-r--    1 mod1421  dba             263 Dec 06 12:07 03_vardemo.ksh