function valid_ipv4 --description "Validate IPv4 address" -a ipv4addr

if test -z "$ipv4addr"
  return 1
end

if not string match -rq '^([0-9]{1,3}\.){3}[0-9]{1,3}$' -- $ipv4addr
  return 1
end

for quadpart in (string split . -- $ipv4addr)
  if not string match -rq '^(0|[1-9][0-9]{0,2})$' -- $quadpart
    return 1
  end

  if test $quadpart -gt 255; or test $quadpart -lt 0
    return 1
  end
end

return 0

end

function reverse_ipv4 --description "Print reverse IPv4 address" -a ipv4addr

if test -z "$ipv4addr"
  return
end

set -l index '4'
set -l rquad '' '' '' ''

for item in (string split --right --max 3 . $ipv4addr)
 set rquad[$index] $item
 set index (math $index-1)
end

echo "$rquad[1].$rquad[2].$rquad[3].$rquad[4]"

end