myhome/.local/bin/mask2cidr

21 lines
798 B
Plaintext
Raw Permalink Normal View History

#!/bin/bash
mask2cidr() {
local mask=$1
# In RFC 4632 netmasks there's no "255." after a non-255 byte in the mask
local left_stripped_mask=${mask##*255.}
local len_mask=${#mask}
local len_left_stripped_mask=${#left_stripped_mask}
local conversion_table=0^^^128^192^224^240^248^252^254^
local number_of_bits_stripped=$(((len_mask - len_left_stripped_mask) * 2))
local signifacant_octet=${left_stripped_mask%%.*}
local right_stripped_conversion_table=${conversion_table%%$signifacant_octet*}
local len_right_stripped_conversion_table=${#right_stripped_conversion_table}
local number_of_bits_from_conversion_table=$((len_right_stripped_conversion_table / 4))
echo $((number_of_bits_stripped + number_of_bits_from_conversion_table))
}
mask2cidr "$@"