Bash Loops

For Loops

For loops allow you to iterate over a list of items or a range of numbers. They are useful for repeating tasks a specific number of times.

The for keyword is followed by a variable name, a range of values, and a do keyword, which marks the start of the loop block.

# For loop example
for i in {1..5}; do
  echo "Iteration $i"
done

While Loops

While loops execute a block of code as long as a specified condition is true.

They are useful for tasks that need to repeat until a certain condition changes.

The condition is enclosed in square brackets [ ], and the loop ends with done.

# While loop example
count=1
while [ $count -le 5 ]; do
  echo "Count is $count"
  ((count++))
done

Until Loops

Until loops are similar to while loops, but they execute until a specified condition becomes true.

The condition is enclosed in square brackets [ ], and the loop ends with done.

# Until loop example
count=1
until [ $count -gt 5 ]; do
  echo "Count is $count"
  ((count++))
done

Break and Continue

Break and continue statements are used to control loop execution. break exits the loop, while continue skips to the next iteration.

These statements are typically used inside conditional blocks to alter the flow of the loop.

# Break and continue example
for i in {1..5}; do
  if [ $i -eq 3 ]; then
    continue
  fi
  echo "Number $i"
  if [ $i -eq 4 ]; then
    break
  fi
done

Nested Loops

Nested loops allow you to place one loop inside another, enabling more complex iteration patterns.

Each loop must be closed with its own done.

# Nested loops example
for i in {1..3}; do
  for j in {1..2}; do
    echo "Outer loop $i, Inner loop $j"
  done
done