For Loop in Bash Script (Shell Scripting)

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For Loop in Bash Script 

(Shell Script)

Shell Scripting Tutorial

For Loop

• It is an example of looping statement and alternative for while loop

• It is used to execute group of statements based on the looping condition

• Bash supports several examples of for-loops. Some of them below

• Simple for loop

• Range based for loop

• C Style based for loop

• Infinite for loop.

1. Simple for loop (Data based for loop)

• Here the loop is based on the data or collection. The data can be the same type or different type.

Syntax

for variable in data

do

# code

done

Where,

variable is an user defined variable.

Example 1 - Data based for loop

Source Code

echo "--------------------------------"

echo -e "\t Data based For Loop"

echo "--------------------------------"

for i in 12 true "Hello" 34.55

do

    echo " $i"

done

Output

2. Range Based for loop

• Here the loop is based on the three attributes like start, stop and interval.

• These attributes should be enclosed by curly braces such as {start..stop..interval }

• Where,

• Start is an inclusive which is the starting range of number

• Stop is an inclusive which is the ending range of number

• Interval is an optional frequency gap, usually it is 1 by default.

Syntax

for variable in {start..stop..interval}

do

# code

done

Where,

variable is an user defined variable.

NOTE

• Interval is an optional in for loop. 

• By default, it is 1.

Drawback

• Dynamic value ca’t be permitted for attributes like start, stop and interval in the range based for loop

Example 2 - Range based for loop

3. C Style Based For Loop (Three Expression For Loop)

• This is similar to c programming for loop

• It takes three expressions like exp1, exp2, exp3

• Where,

• exp1 is an initial condition

• exp2 is an condition

• exp3 is the either increment or decrement value

Syntax

for ((exp1; exp2; exp3))

do

# code

done

Example 3 - C Style based for loop

Source Code

echo "---------------------------------------"

echo -e "\t C Style Based For loop"

echo "---------------------------------------"

echo "Enter the number: "

read n

f=1

for ((i=1;i<=n;i++))

do

    f=$((f*i))

done

echo "Fact is : $f”

Output

4. Infinite For Loop

• If you don’t mention the start, stop and interval in c style loop, it will be considered as infinite for loop

• Like c programming, just specify two semicolons ;; to display the infinite For loop

• We need to press ctrl+c to terminate / stop the loop.

Syntax

for ((;;))

do

# code

done

Example 4 - Infinite For Loop

Source Code

echo "-----------------------------------"

echo -e "\t Infinite For Loop"

echo "-----------------------------------"

# infinite for loop

for ((;;))

do

    echo "Good Morning"

done

Output