add a number in fish script

Question

I want to have a function that gets the number of lines of output from a command and adds one to it. So far I have this:

function add1
    set num (tmux list-sessions | wc -l)
    echo $num
end

Now how do I add 1 to $num ? (or while I'm assigning the variable)

Answer 1

请参阅用户文档中的math命令：

set num (math $num + 1)