Nesting Loops
A loop statement can use any other type of command within the loop, including other loop commands. This is called a nested loop. Care should be taken when using nested loops, because you're performing an iteration within an iteration, which multiplies the number of times commands are being run. If you don't pay close attention to this, it can cause problems in your scripts.
Here's a simple example of nesting a for loop inside another for loop:
$ cat test14
#!/bin/bash
# nesting for loops
for (( a = 1; a <= 3; a++ ))
do
echo "Starting loop $a:"
for (( b = 1; b <= 3; b++ ))
do
echo " Inside loop: $b"
done
done
$ ./test14
Starting loop 1:
Inside loop: 1
Inside loop: 2
Inside loop: 3
Starting loop 2:
Inside loop: 1
Inside loop: 2
Inside loop: 3
Starting loop 3:
Inside loop: 1
Inside loop: 2
Inside loop: 3
$The nested loop (also called the inner loop) iterates through...