fish-shell/share/functions/seq.fish

    # If seq is not installed, then define a function that invokes __fish_fallback_seq
# We can't call type here because that also calls seq

if not command -sq seq
    # No seq command
    function seq --description "Print sequences of numbers"
        __fish_fallback_seq $argv
    end

    function __fish_fallback_seq --description "Fallback implementation of the seq command"

        set -l from 1
        set -l step 1
        set -l to 1

        switch (count $argv)
            case 1
                set to $argv[1]

            case 2
                set from $argv[1]
                set to $argv[2]

            case 3
                set from $argv[1]
                set step $argv[2]
                set to $argv[3]

            case '*'
                printf (_ "%s: Expected 1, 2 or 3 arguments, got %d\n") seq (count $argv)
                return 1

        end

        for i in $from $step $to
            if not string match -rq '^-?[0-9]*([0-9]*|\.[0-9]+)$' $i
                printf (_ "%s: '%s' is not a number\n") seq $i
                return 1
            end
        end

        if [ $step -ge 0 ]
            echo "for( i=$from; i<=$to ; i+=$step ) i;" | bc
        else
            echo "for( i=$from; i>=$to ; i+=$step ) i;" | bc
        end
    end
end