For a nested loop that uses two or more arrays, e.g.
A=(0.1 0.2)
B=(2 4 6)
AB=$((${#A[@]}*${#B[@]})) # total number of iterations (length of A * length of B)
for a in ${A[*]}; do
for b in ${B[*]}; do
$(($a+$b)) # task using each combination of A and B
echo ? # show number of the iteration (i.e. 1 to length of AB)
done
done
What is the best way to get the number of the iteration, as shown above using echo?
You could do this with a simple counter that is incremented inside the inner loop:
i=0
for a in "${A[@]}"; do
for b in "${B[@]}"; do
((i++))
printf "Iteration: $i\n"
: your code
done
done
This would make sense if all the logic is inside the inner-most loop and if we consider the execution of inner-most loop as one iteration.
Note that you need double quotes around array reference to prevent word splitting and globbing. Also, I think you need array[@] rather than array[*] as long as you want each element separately and not a concatenated version of all elements.
set -e (exit on error), then nothing is printed. While obviously not critical, is this indicating that there is an imperfection with this code?
set -e if you start at i=1 and use ((++i)). Why is not clear to me, though.Based on the example given and the method suggested by @codeforester, this is what worked for me (with set -e included near the start of the script).
i=1
for a in ${A[*]}; do
for b in ${B[*]}; do
I=$((i++))
echo "Iteration: $I"
echo "Combination: $a $b" # show combination of A and B elements
# task code
done
done
In this example, array[*] without the double quotes produced the desired result, using each element separately within the loop to produce unique combinations of A and B values, while finding each iteration number within the nested loop.