Linux Shell Script Programs and Examples
Brief:
A simple script to print Hello World on terminal using echo command
Source Code:
#!/bin/bash
#
# Author : Emertxe (https://www.emertxe.com)
# Date : Tue 16 Feb 2016 16:27:07 IST
# File : ls_001_ch6_hello_world.sh
# Title : Hello World
# Description : A simple script to print Hello World on terminal using echo command
#
echo "Hello World"
Example output:
Brief:
A simple script to print the calender month by default.
Source Code:
#!/bin/bash
#
# Author : Emertxe (https://www.emertxe.com)
# Date : Tue 16 Feb 2016 16:27:07 IST
# File : ls_002_ch6_calender.sh
# Title : Calender
# Description : A simple script to print the calender month by default
#
echo "The Month is"
cal # cal command displays current month by default
echo "An alternate view of calender"
ncal # An alternale layout for calender
Example output:
Brief:
A simple script to read user input and perform operations with them.
Source Code:
#!/bin/bash
#
# Author : Emertxe (https://www.emertxe.com)
# Date : Tue 16 Feb 2016 16:27:07 IST
# File : ls_003_ch6_variables_and_expressions.sh
# Title : Variables and Expressions
# Description : A simple script to read user input and perform operations with them
#
echo -n "Enter number 1 : " # -n option supresses newline
read NUM1 # Read the user input from Standard Input and store in Variable NUM1
echo -n "Enter number 2 : "
read NUM2
SUM=$(($NUM1 + $NUM2)) # Arithmetic expansion using double parentheses
echo "The sum is $SUM"
SUM=`expr $NUM1 + $NUM2` # Arithmetic expansion using backticks.
#Usage of expr command to evaluate the expression
echo "The sum is $SUM"
Example output:
Brief:
A script to show usage of if condition
Source Code:
#!/bin/bash
#
# Author : Emertxe (https://www.emertxe.com)
# Date : Tue 16 Feb 2016 16:27:07 IST
# File : ls_004_ch6_if.sh
# Title : Test construct - if
# Description : A script to show usage of if condition
#
NUM1=5 # variabe assignment
NUM2=2
if [ $NUM1 -gt $NUM2 ] # -gt is to test intiger numbers
then
echo "NUM1 > NUM2"
fi
Example output:
Brief:
A script to show usage of if else condition
Source Code:
#!/bin/bash
#
# Author : Emertxe (https://www.emertxe.com)
# Date : Tue 16 Feb 2016 16:27:07 IST
# File : ls_005_ch6_if_else.sh
# Title : Test construct - if else
# Description : A script to show usage of if else condition
#
NUM1=2 # Variabe assignment
NUM2=5
if [ $NUM1 -lt $NUM2 ] # -lt is to test intiger numbers
then
echo "NUM1 < NUM2"
else
echo "NUM1 > NUM2"
fi
Example output:
Brief:
A script to show usage of else if condition
Source Code:
#!/bin/bash
#
# Author : Emertxe (https://www.emertxe.com)
# Date : Tue 16 Feb 2016 16:27:07 IST
# File : ls_006_ch6_elif.sh
# Title : Test construct - elif (else if)
# Description : A script to show usage of else if condition
#
echo -n "Enter a number: "
read NUM
if [ $NUM -gt 0 ]
then
echo "$NUM is +ve"
elif [ $NUM -lt 0 ]
then
echo "$NUM is -ve"
else
echo "$NUM is 0"
fi
echo "done"
Example output:
Brief:
A script to demonstrate case statement
Source Code:
#!/bin/bash
#
# Author : Emertxe (https://www.emertxe.com)
# Date : Tue 16 Feb 2016 16:27:07 IST
# File : ls_007_01_ch6_switch_case.sh
# Title : Test and Branch constuct - Case
# Description : A script to demonstrate case statement
#
echo -n "Enter a character: "
read CHAR
case $CHAR in
a) echo "You entered $CHAR which is a vowel";; # ;; Terminates each option
e) echo "You entered $CHAR which is a vowel";;
i) echo "You entered $CHAR which is a vowel";;
o) echo "You entered $CHAR which is a vowel";;
u) echo "You entered $CHAR which is a vowel";;
*) echo "You entered $CHAR which is not a vowel";; # Defaults to everything else
esac
echo "What if you enter upper case letters!!?, Check the next example"
Example output:
Brief:
A script to demonstrate case statement
Source Code:
#!/bin/bash
#
# Author : Emertxe (https://www.emertxe.com)
# Date : Tue 16 Feb 2016 16:27:07 IST
# File : ls_007_02_ch6_switch_case.sh
# Title : Test and Branch constuct - Case
# Description : A script to demonstrate case statement
#
echo -n "Enter a character: "
read CHAR
case $CHAR in
a | A) # Test for both Lower or Upper case letter
# You may write commands in this fashion too!!, means multiline commands
echo "You entered $CHAR which is a vowel"
;; # Terminates each option
e | E)
echo "You entered $CHAR which is a vowel"
;;
i | I)
echo "You entered $CHAR which is a vowel"
;;
o | O)
echo "You entered $CHAR which is a vowel"
;;
u | U)
echo "You entered $CHAR which is a vowel"
;;
*) # Defaults to everything else
echo "You entered $CHAR which is not a vowel"
;;
esac
Example output:
Brief:
A script to demonstrate case statement
Source Code:
#!/bin/bash
#
# Author : Emertxe (https://www.emertxe.com)
# Date : Tue 16 Feb 2016 16:27:07 IST
# File : ls_007_03_ch6_switch_case.sh
# Title : Test and Branch constuct - Case
# Description : A script to demonstrate case statement with string inputs
#
echo -n "Oceans are larger than lakes (True or False) : "
read USER_INPUT
case $USER_INPUT in
"TRUE"| "True" | "true")
echo "Yes you are right"
;; # Terminates each option
"FALSE" | "Fasle" | "false")
echo "No your are wrong"
;;
*) # Defaults to everything else
echo "Please enter either True or False"
;;
esac
Example output:
Brief:
A simple script to show usage of string compare operator = and !=
Source Code:
#!/bin/bash
#
# Author : Emertxe (https://www.emertxe.com)
# Date : Tue 16 Feb 2016 16:27:07 IST
# File : ls_008_01_ch6_stings.sh
# Title : Operators - String Compare
# Description : A simple script to show usage of string compare operator = and !=
#
STR1="Hello"
STR2="Hello"
if [ ${STR1} = ${STR2} ]
then
echo "Strings match"
else
echo "Strings don't match"
fi
Example output:
Brief:
A simple script to show usage of string compare operator -z and -n
Source Code:
#!/bin/bash
#
# Author : Emertxe (https://www.emertxe.com)
# Date : Tue 16 Feb 2016 16:27:07 IST
# File : ls_008_02_ch6_stings.sh
# Title : Operators - String Compare
# Description : A simple script to show usage of string compare operator -z and -n
#
STR1="Hello"
STR2="Hello"
if [ -z "${STR1}" ]
then
echo "String1 is empty"
else
echo "String1 is NOT empty"
fi
echo ":$STR:"
if [ -n "${STR2}" ]
then
echo "String2 is NOT empty"
else
echo "String2 is empty"
fi
Example output:
Brief:
A simple script to show usage of logical operators
Source Code:
#!/bin/bash
#
# Author : Emertxe (https://www.emertxe.com)
# Date : Tue 16 Feb 2016 16:27:07 IST
# File : ls_009_ch6_logical_operators.sh
# Title : Operators - Logical
# Description : A simple script to show usage of logical operators
#
echo -n "Enter a NUM: "
read NUM
# Check whether a number is between 10 and 20 (Using AND -a operator)
if [ $NUM -ge 10 -a $NUM -le 20 ]
then
echo "$NUM is between 10 and 20"
else
echo "$NUM is NOT between 10 and 20"
fi
echo -n "Enter another NUM: "
read NUM
# Check whether a number is between 10 and 20 (Using OR -o operator)
if [ $NUM -lt 10 -o $NUM -gt 20 ]
then
echo "$NUM is NOT between 10 and 20"
else
echo "$NUM is between 10 and 20"
fi
Example output:
Brief:
A simple script to show usage while loop
Source Code:
#!/bin/bash
#
# Author : Emertxe (https://www.emertxe.com)
# Date : Tue 16 Feb 2016 16:27:07 IST
# File : ls_010_01_ch6_while_loop.sh
# Title : Loops - while
# Description : A simple script to show usage while loop
#
COUNT=0
while [ $COUNT -lt 5 ]
do
echo "Loop count is ${COUNT}"
COUNT=$((COUNT + 1))
done
echo "Done"
Example output:
Brief:
Sum of N natural numbers using while loop
Source Code:
#!/bin/bash
#
# Author : Emertxe (https://www.emertxe.com)
# Date : Tue 16 Feb 2016 16:27:07 IST
# File : ls_010_02_ch6_while_loop.sh
# Title : Loops - while
# Description : Sum of N natural numbers using while loop
#
echo -n "Enter a number: "
read NUM
let SUM=0;
let I=1
while [ $I -le $NUM ]
do
SUM=`expr $SUM + $I`
I=$((${I} + 1))
done
echo "The sum of the first $NUM numbers is: $SUM"
Example output:
Brief:
A simple script to demonstarte for loop [ Bash syntax ]
Source Code:
#!/bin/bash
#
# Author : Emertxe (https://www.emertxe.com)
# Date : Tue 16 Feb 2016 16:27:07 IST
# File : ls_011_01_ch6_for_loop.sh
# Title : Loops - for
# Description : A simple script to demonstarte for loop [ Bash syntax ]
#
COUNT=0
for i in 0 1 2 3 4
do
echo "Loop count is ${COUNT}"
COUNT=$((COUNT + 1))
done
Example output:
Brief:
A simple script to demonstarte for loop [ C syntax ]
Source Code:
#!/bin/bash
#
# Author : Emertxe (https://www.emertxe.com)
# Date : Tue 16 Feb 2016 16:27:07 IST
# File : ls_011_02_ch6_for_loop.sh
# Title : Loops - for
# Description : A simple script to demonstarte for loop [ C syntax ]
#
COUNT=0
for ((i = 0; i < 5; i++))
do
echo "Loop count is ${COUNT}"
COUNT=$((COUNT + 1))
done
Example output:
Brief:
Sum of N natural numbers using for loop
Source Code:
#!/bin/bash
#
# Author : Emertxe (https://www.emertxe.com)
# Date : Tue 16 Feb 2016 16:27:07 IST
# File : ls_011_03_ch6_for_loop.sh
# Title : Loops - for
# Description : Sum of N natural numbers using for loop
#
echo -n "Enter a number: "
read NUM
let SUM=0;
for I in `seq $NUM` # seq command provides a sequence of numbers from 0 to $NUM
do
SUM=`expr $SUM + $I`
I=$((${I} + 1))
done
echo "The sum of the first $NUM numbers is: $SUM"
Example output:
Brief:
A script to show the usage of command line arguments, Here we access positional arguments using $1, $2 …
Source Code:
#!/bin/bash
#
# Author : Emertxe (https://www.emertxe.com)
# Date : Tue 16 Feb 2016 16:27:07 IST
# File : ls_012_01_ch6_cmd_line_agrs.sh
# Title : Command line arguments
# Description : A script to show the usage of command line arguments,
# Here we access positional arguments using $1, $2 ...
echo "Total no. of argument: $#"
echo "Program name: $0"
echo "1st argument: $1"
echo "2nd argument: $2"
echo "3rd argument: $3"
Example output:
Brief:
A script to show the usage of command line arguments, Here we access arguments by iterating over $@
Source Code:
#!/bin/bash
#
# Author : Emertxe (https://www.emertxe.com)
# Date : Tue 16 Feb 2016 16:27:07 IST
# File : ls_012_02_ch6_cmd_line_agrs.sh
# Title : Command line arguments
# Description : A script to show the usage of command line arguments, Here we access arguments by iterating over $@
#
echo "Total no. of argument: $#"
echo "Argument list: $@" # Commonly used
echo "Argument list: $*"
# Iterate over arguments ($@)
for ARG in $@
do
echo $ARG
done
Example output:
Brief:
A script to show the usage of function
Source Code:
#!/bin/bash
#
# Author : Emertxe (https://www.emertxe.com)
# Date : Tue 16 Feb 2016 16:27:07 IST
# File : ls_013_01_ch6_function.sh
# Title : Functions
# Description : A script to show the usage of function
#
# Function definition
function print_hello()
{
echo "====="
echo "Hello"
echo "====="
}
# Call the function - print_hello
print_hello
#print_hello
Example output:
Brief:
A script to show the usage of function and how to pass arguments
Source Code:
#!/bin/bash
#
# Author : Emertxe (https://www.emertxe.com)
# Date : Tue 16 Feb 2016 16:27:07 IST
# File : ls_013_02_ch6_function.sh
# Title : Functions - Arguments
# Description : A script to show the usage of function and how to pass arguments
#
# Function definition
function find_sum()
{
SUM=`expr $1 + $2`
echo $SUM
}
# Pass arguments 10 and 20 to find_sum function
find_sum 10 20
# Save the output of function in a variable
RESULT=`find_sum 100 200`
echo $RESULT
Example output:
Brief:
A script to show the usage of function and how to pass arguments Inside function:
$# – Gives no. of arguments
$@ – Contains the arguments to function
Accessing function arguments is similar to accessing command line arguments
Source Code:
#!/bin/bash
#
# Author : Emertxe (https://www.emertxe.com)
# Date : Tue 16 Feb 2016 16:27:07 IST
# File : ls_013_03_ch6_function.sh
# Title : Functions - Arguments
# Description : A script to show the usage of function and how to pass arguments
# Inside function:
# $# - Gives no. of arguments
# $@ - Contains the arguments to function
# Accessing function arguments is similar to accessing command line arguments
#
# Function definition
function find_sum()
{
echo "Arg count: $#"
echo "Arg list: $@"
SUM=0
# Iterate over function arguments
for ARG in $@
do
SUM=`expr $ARG + $SUM`
done
echo $SUM
}
# Call find_sum with many arguments
find_sum 1 2 3 4 5
find_sum 10 20
Example output:
Brief:
A script to show how to declare an array and access its elements
Source Code:
#!/bin/bash
#
# Author : Emertxe (https://www.emertxe.com)
# Date : Tue 16 Feb 2016 16:27:07 IST
# File : ls_014_01_ch6_array.sh
# Title : Array
# Description : A script to show how to declare an array and access its elements
#
# Declare an array
FRUITS=(apple mango banana orange)
# Print value of each element
echo "element 0: ${FRUITS[0]}"
echo "element 1: ${FRUITS[1]}"
echo "element 2: ${FRUITS[2]}"
echo "element 3: ${FRUITS[3]}"
# Print size / length of array
echo "Length: ${#FRUITS[@]}"
echo "Whole array: ${FRUITS[@]}"
echo "Whole array: ${FRUITS[*]}"
echo "Looping over array elements"
# Iterate over array elements
for ITEM in ${FRUITS[@]}
do
echo $ITEM
done
Example output:
Brief:
A script to store all cmd line arguments to a array and prints
Source Code:
#!/bin/bash
#
# Author : Emertxe (https://www.emertxe.com)
# Date : Tue 16 Feb 2016 16:27:07 IST
# File : ls_014_02_ch6_array.sh
# Title : Array
# Description : A script to store all cmd line arguments to a array and prints
#
ARG=($*)
echo ${ARG[0]}
echo ${ARG[1]}
echo ${ARG[2]}
echo ${ARG[3]}
echo ${ARG[4]}
Example output:
Brief:
A script to demonstrate different types of array access
Source Code:
#!/bin/bash
#
# Author : Emertxe (https://www.emertxe.com)
# Date : Tue 16 Feb 2016 16:27:07 IST
# File : ls_014_03_ch6_array.sh
# Title : Array
# Description : A script to demonstrate different types of array access
#
array=(zero one two three four five)
# Element 0 1 2 3 4 5
echo ${array[0]} # zero
echo ${array:0} # zero, Parameter expansion of first element,+ starting at position # 0 (1st character).
echo ${array:1} # ero, Parameter expansion of first element, + starting at position # 1 (2nd character).
echo "--------------"
echo ${#array[0]} # 4, Length of first element of array.
echo ${#array} # 4, Length of first element of array. (Alternate notation)
echo ${#array[1]} # 3, Length of second element of array. Arrays in Bash have zero-based indexing.
echo ${#array[*]} # 6, Number of elements in array.
echo ${#array[@]} # 6, Number of elements in array.
echo "--------------"
# Quoting permits embedding whitespace within individual array elements.
array2=([0]="first element" [1]="second element" [3]="fourth element")
echo "The ${array2[0]}" # first element
echo "The ${array2[1]}" # second element
echo "The ${array2[2]}" # Skipped in initialization, and therefore null.
echo "The ${array2[3]}" # fourth element
echo "The lenght of ${array2[0]} ${#array2[0]}" # 13 (length of first element)
echo "The number of elements in the array ${#array2[*]}" # 3 (number of elements in array)
Example output:
Brief:
A script to demostrate usage of sed command
Source Code:
#!/bin/bash
#
# Author : Emertxe (https://www.emertxe.com)
# Date : Tue 16 Feb 2016 16:27:07 IST
# File : ls_015_ch6_sed.sh
# Title : Command - sed
# Description : A script to demostrate usage of sed command
#
# Uses printf to color the pattern
echo "I am in GREEN" | sed ''/GREEN/s//`printf " 33[32mGREEN 33[0m"`/''
Example output:
