Loops

Bash loops come in the general format for / do / done. They also support break and continue statements, which break out of the loop and skip to the next iteration, respectively.

C-style loops

Bash supports C-style loops, with an initializer expression, a conditional expression, and a counting expression:

for (( i=0; i<=9; i++ ))
do  
  echo "Loop var i is currently $i"
done

for…in

Let’s talk about iteration with for...in loops. Try running the following in your shell:

for i in 1 2 3 4 5
do
  echo $i
done

Here’s a loop with some control flow inside:

for os in FreeBSD Linux NetBSD "macOS" DragonflyBSD
do
  echo "Checking out ${os}..."
  if [[ "$os" == 'NetBSD' ]]; then
    echo "(I'm pretty sure this would run on my toaster, actually)"
  fi
  sleep 1
done

While

Another common control structure you might be familiar with from other programming languages...