As you may know, the famous factorial can be done in Recursion via:
where 
BASH supports function declaration and recursion – just like other modern programming language. See below the Recursive function to compute the factorial values.
#!/bin/bash
function f() {
local n=$1
if [[ $n -eq 0 ]]; then
echo 1
else
echo $((n*$(f $n-1)))
fi
}
for i in {1..10}; do
echo "$i!=$(f $i)"
done
This BASH script prints the first 10 factorial numbers:
1!=1
2!=2
3!=6
4!=24
5!=120
6!=720
7!=5040
8!=40320
9!=362880
10!=3628800
We use “local” to keep the variables at scope of function, and we can use $() to call a function recursively.
See also: Teaching Kids Programming – Recursion in Five Minutes
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