Question

I have a problem with writing it in bash… I know how it works in C++, but I have trouble implementing it in bash. Here’s what I got:

sum() 
{
    let minusOne=$1-1
    let result=sum $minusOne +$1

}

Answer 1

You need an exit condition. In bash, $((...)) is arithmetic expansion, and $(...) is command substitution (see the man page).

sum() {
    if (( $1 == 1 )); then
        echo 1
        return
    fi
    local minusOne=$(( $1 - 1 ))
    echo $(( $1 + $(sum $minusOne) ))
}

A non-recursive way to write a sum function:

sum() {
  set -- $(seq 1 $1)
  local IFS=+
  echo "$*" | bc
}