http://web.theurbanpenguin.com/training/scripting/mastering-bash-shell-scripting/
http://web.theurbanpenguin.com/category/bash-scripting/
http://web.theurbanpenguin.com/category/bash-scripting/
if statements
//////////////////////////////
syntax
if [ expression ];
then
statements
fi
//////////////////////////////
example 1
read -p "Enter number:" number
if [ $number -gt 123 ];
then
echo "value is greater than 123"
fi
o/p:value is greater than 123
////////////////////////////////////
example 2
if [ "myfile" == "myfile" ];
then
echo "its true"
fi
o/p:its true
//////////////////////////////////
For using multiple conditions with AND operator:
''''''''''''''''''''''''''''''''''''''''''''''''''''''
if [ expression_1 ] && [ expression_2 ];
then
statements
fi
example 1
if [ 1 -lt 10 ] && [ 100 -gt 10 ];
then
echo "we won"
fi
o/p: we won
////////////////////////////
For using multiple conditions with OR operator:
if [ expression_1 ] || [ expression_2 ];
then
statements
fi
case statement example
echo "Enter the arithmetic operation you want to perform?"
echo "A for ADD, S for SUBTRACTION, M FOR MULTIPLY, D FOR DIVISION"
echo "Enter the operands "
read x
read y
read -p "A|S|M|D" val
case $val in
A|a)
sum=$((y+x))
echo $sum
;;
S|s)
((sub=$x-$y))
echo " Subtraction of $x - $y =$sub"
;;
M|m)
((mul=$x*$y))
echo " Multiplication of $x * $y =$mul"
;;
D|d)
((div=$x/$y))
echo "Division of $x/$y =$div"
;;
esac
forloop
**********************************
syntax
for (( expression1; expression2; expression3 ))
do
commands
done
///////////////////////////////////////
example 1
echo "FINDING SUM OF N NUMBERS"
read x
sum=0
for (( i=0; i<=x; i++ ))
do
((sum=sum+i))
done
echo "$sum"
o/p x=5
15
//////////////////////////////////////
syntax
for variable in list
do
commands
done
example
for num in {1..10}
do
echo $num
done
echo"series of numbers from 1 to 10"
o/p:
1
2
3
4
5
6
7
8
9
10
////////////////////////////////////////////////
For Loop to Read Array Variables
syntax
array=( "element1" "element 2" . . "elementN" )
for i in "${arr[@]}"
do
echo $i
done
example
arr=( "sun" "moon" "earth" "mars" "venus" "mercury" )
for i in "${arr[@]}"
do
echo $i
done
o/p
sun
moon
earth
mars
venus
mercury
/////////////////////////////////////////////////
For Loop with a Continue Statement
use the 'continue' statement inside the 'for' loop to skip any specific statement on a particular condition. It tells Bash to stop executing that particular iteration of the loop and process the next iteration.
example program to print Numbers from 1 to 20, ignoring from 6 to 15 using continue statement"
for ((i=1; i<=20; i++));
do
if [[ $i -gt 5 && $i -lt 16 ]];
then
continue
fi
echo $i
done
///////////////////////////////////////////////////////////////////
For Loop with a Break Statement
A 'break' statement can be used inside 'for' loop to terminate from the loop.
example
#!/bin/bash
#Table of 2
for table in {2..100..2}
do
echo $table
if [ $table == 20 ]; then
break
fi
done
o/p:
2
4
6
8
10
12
14
16
18
20
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
Infinite Bash For Loop
When there is no 'start, condition, and increment' in the bash three expressions for loop, it becomes an infinite loop. To terminate the infinite loop in Bash, we can press Ctrl+C.
example
i=1;
for (( ; ; ))
do
sleep 1s
echo "Current Number: $((i++))"
done
Bash While Loop
****************************
while [ condition ];
do
commands;
done
example
#!/bin/bash
#Script to get specified numbers
read -p "Enter starting number: " snum
read -p "Enter ending number: " enum
while [[ $snum -le $enum ]];
do
echo $snum
((snum++))
done
echo "This is the sequence that you wanted."
o/p
Enter starting number: 2
Enter ending number: 9
2
3
4
5
6
7
8
9
This is the sequence that you wanted.
////////////////////////////////////////////////////////////
Infinite While Loop
An infinite loop is a loop that has no ending or termination. If the condition always evaluates to true, it creates an infinite loop.
example
#!/bin/bash
#An infinite while loop
while :;
do
echo "YOU r in a loop.";
done
