Lesson 4: Bash Control Structures – loops (for, while, until)

For Loop

The for loop is used to iterate over a list of items. It is particularly useful when you know the number of iterations in advance. Here’s the basic syntax:

Basic syntax

for item in list
do
    # Commands to execute
done

Example

for i in {1..5}
do
    echo "Iteration $i"
done

Output

Iteration 1
Iteration 2
Iteration 3
Iteration 4
Iteration 5

While Loop

The while loop continues to execute as long as a specified condition is true. It is useful when the number of iterations is not known beforehand.

Basic syntax

while [ condition ]
do
    # Commands to execute
done

Example

count=1
while [ $count -le 5 ]
do
    echo "Count is $count"
    ((count++))
done

This loop will print the count from 1 to 5.

Until Loop

The until loop is similar to the while loop, but it continues to execute as long as the specified condition is false.

Basic syntax

until [ condition ]
do
    # Commands to execute
done

Example

count=1
until [ $count -gt 5 ]
do
    echo "Count is $count"
    ((count++))
done

This loop will also print the count from 1 to 5.

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