source: vendor/bash/3.1/examples/functions/inpath

inpath()
{
        local PROG
        path=$(echo $PATH | sed 's/^:/.:/
                                s/::/:.:/g
                                s/:$/:./
                                s/:/ /g')

        for x in $path
        do
                [ -x $x/$1 ] && { PROG=$x/$1; break; }
        done
        [ -n "$PROG" ]
}