01.for_while_until_loops.md

Loops in Linux

1. For Loop

The for loop in Bash is used to iterate over a sequence of values. It has the following syntax:

for variable in sequence
do
    # Commands to be executed for each iteration
done

• variable: Represents the loop variable that takes each value in the specified sequence.
• sequence: Can be a range of numbers, a list of items, or the output of a command.

Example:

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

This will print:

Iteration 1
Iteration 2
Iteration 3
Iteration 4
Iteration 5

2. While Loop

The while loop in Bash continues to execute a block of commands as long as a specified condition is true. Here is the basic syntax:

while [ condition ]
do
    # Commands to be executed as long as the condition is true
done

• condition: Represents the test that determines whether the loop continues or terminates.

Example:

counter=1
while [ $counter -le 5 ]
do
    echo "Iteration $counter"
    ((counter++))
done

This will print the same output as the previous for loop example.

3. Until Loop

The until loop is similar to the while loop, but it continues to execute a block of commands as long as a specified condition is false. The syntax is as follows:

until [ condition ]
do
    # Commands to be executed as long as the condition is false
done

Example:

counter=1
until [ $counter -gt 5 ]
do
    echo "Iteration $counter"
    ((counter++))
done

This will also produce the same output as the previous examples.

Conclusion

Understanding the for, while, and until loops in Bash is crucial for efficient scripting in Linux. These constructs provide flexibility in handling repetitive tasks and iterating over data, making them fundamental elements in shell scripting/Linux.

Next | Loop control statements (break, continue)