Shell scripting for beginners

gistfile1.txt

#! /bin/bash

#Created by following tutorials by https://www.youtube.com/channel/UCs6nmQViDpUw0nuIx9c_WvA Programming Knowledge

# echo "hello world"

# echo "Enter names: "
# read name1 name2 name3
# echo "Name : $name1 , $name2 , $name3"

# read -p 'username :' user_var  #-p to get input in the same line
# read -sp 'password' pass_var   #s for silent
# echo 							 #for blank line
# echo username $user_var
# echo password $pass_var


# echo "Enter names :"
# read -a names 					#a for array
# echo Names ${names[0]} , ${names[1]}

# echo "Enter name"
# read
# echo Name $REPLY		#reply is the default variable for input in case you don't specify any variable 

# echo  $0 $1 $2 $3 		#value of first argument(flag) goes to $1 second to $2 and so on
						#$0 contains the value of command executed i.e ./hello.sh in this case

# args=("$@")  			#to get the value of argum
# echo ${args[0]} ${args[1]} ${args[2]} 
# echo $@ 				#to print all the arguments
# echo $#					#to print the number og arguments


#	(( )) --> for inequality 
#	[] otherwise

# count=10
# if (( $count > 10 ))
# then
# 	echo "true"
# fi

# string=abc

# if [ $string = "abc" ]  
# then
# 	echo "true"
# fi


# echo -e "enter the file name \c" 		# \c to keep the cursor in the same line  but it won't interpret escape sequences without -e
# read file_name

# if [ -e $file_name ]					# -e flag to check if file exists
# then									# -f flag to check if file exists and it is regular file
# 	echo $file_name found				# -d for directory -b block special -c character special -s to check if file is empty
# else
# 	echo $file_name not found			#-w for write permission 
# fi


# > file will be overwritten
# >> data will be appended to the file

# echo -e "enter file_name \c"
# read file_name
# if [ -f $file_name ]
# 	then
# 	if [ -w $file_name ]
# 		then
# 		echo "enter the data you want to append to this file. Press ctrl+d to exit"
# 		cat >> $file_name
# 	else
# 		echo "write permission denied"
# 	fi
# else
# 	echo "file not found"
# fi


# age=25

# if (( $age > 20 )) && (( $age < 30 ))
# 	then 
# 	echo "valid age"
# else
# 	echo "invalid age"
# fi

#arithmetic operations
#num1=20
# num2=5
# echo $(( num1 + num2 ))
# echo $( expr $num1 + $num2 )  #for multiplication * won't work use \*

#for decimal numbers we will use bc(basic calculator) 
# whatever is written on the left side of | acts as input for the right side

# echo 5.2+7.3 | bc
# echo "scale=2;4.5/9" | bc   	#scale sets the number of digits after decimal
# echo "scale=2;sqrt($num1)" | bc -l  #-l to include the math library of bc which contains the function sqrt
# echo "scale=2;3^3" | bc -l

# vehicle=$1

# case $vehicle  										#switch case
# 	"car" )
# 		echo "rent of $vehicle is 100 dollar" ;;
# 	"van" )
# 		echo "Rent of $vehicle is 80 dollar" ;;
# 	* )
# 		echo "unknown";;
# esac 

# echo -e "Enter some character \c"
# read value

# case $value in 										
# 	[a-z] )		
# 		echo "user entered $value a to z ";;		#[a-z] pattern recog
# 	[A-Z] )
# 		echo "user entered $value A to Z";;  		#in case it doesn't work set LANG=c in terminal 
# 	[0-9] )
# 		echo "user entered $value 0-9";;
# 	? )
# 		echo "special character";;
# 	* )
# 		echo unknown;;
# esac

# os=('ubuntu' 'mac' 'windows')  #initiating array 
# os[6]='kali'					#adding elements----gaps are allowed in an array
# unset os[2]						#deleting an element
# echo "${os[@]}"					#print all the elements of array
# echo "${!os[@]}"				#print indices 
# echo "${#os[@]}"				#print length

#we can also acess strigs index wise

# n=1

# while (( $n < 10 ))
# do
# 	echo $n
# 	(( n++ ))				#n=$(( n+1 ))
# done

# sleep 1   #will sleep for 1 second
# gnome-terinal  #to open a new terminal

#reading file

# while read p 		#reading a file line by line
# do
# 	echo $p
# done < hello.sh  #this data is read by p

# cat hello.sh | while read p    #content read using cat command is used a input for while command
# do
# 	echo $p 
# done

# while IFS=' ' read -r p    #to read escape sequences -r pevents /escape to be interpreted  
# do
# 	echo $p 
# done < hello.sh

# num=1
# until (( num == 2 )) 	#commands in this loop are executed when the conditions are false
# do
# 	echo "$num"
# 	(( num++ ))
# done

#for loops
# for i in 1 2 3 4 5
# do 
# 	echo $i
# done 

# for i in {1..10..2}       #a..b..c a->starting value  b->ending value  c->value by which i is incremented
# do  						# we can skip c and it will be defaulted to 1
# 	echo $i
# done

# for (( i=0; i<5; i++))
# do
# 	echo $i
# done


# for command in ls pwd date 
# do
# 	echo "-----$command----------"   #to print the name of command
# 	$command 						#to execute the command
# done

# for item in *						# * would give all the items
# do
# 	if [ -d $item ]					#to check if item is directory
# 		then
# 		echo $item
# 	fi
# done

#select loop

# select name in mark john tom ben
# do
# 	echo "$name selected"
# done

# select name in mark john tom ben
# do
# 	case $name in
# 		mark )
# 			echo mark selected
# 			;;
# 		john )
# 			echo john selected
# 			;;
# 		ben )
# 			echo ben selected
# 			;;
# 		tom )
# 			echo tom selected
# 			;;
# 		* ) 
# 			echo "error";;
# 	esac
# done

#break and continue condition 

# for (( i=0; i<10; i++))
# do
# 	if [ $i == 0 ]
# 	then
# 		continue
# 	fi
# 	echo $i
# 	if (( $i > 5 ))
# 		then
# 		break
# 	fi
# done

#functions

# function Hello(){
# 	echo "hello"
# 	echo $1	
# }

# quit () {		#another way of declaring functions
# 	exit
# }

# Hello test     #test 1 the argument passed with function
# quit
# echo "he"

#function example 

# is_file_exist()
# {
# 	local file=$1  			#local is used to set the scope of variable local. By default it is global
# 							# $1 here is the argument passed to this function
# 							# and not the argument passed with command in terminal
# 	[[ -f "$file" ]] && return 0 || return 1
# }

# if(is_file_exist $1)
# 	then 

# 	echo "File found"
# else
# 	echo "File not found"
# fi