Bash: Loops

For loops

The generic form of a for loop is:

for ELEM in LIST
do
    ...
done

However, the in LIST part is optional. When it’s not present, then it’s assumed to be in "$@". So the following for loops are equivalent:

for ELEM
do
    ...
done

for ELEM in "$@"
do
    ...
done

While loops

A basic while loop for a countdown is:

i=3
while (( $i >= 0 ))
do  
    printf "$i\n"
    i=$((i - 1))
done

3
2
1
0

and there is an until form that we can also use:

i=3
until (( $i == -1 ))
do
    printf "$i\n"
    i=$((i - 1))
done

3
2
1
0