shell实现netmask掩码和cidr掩码位转换

#!/bin/bash
mask2cdr ()
{
    # Assumes there's no "255." after a non-255 byte in the mask
    local x=${1##*255.}
    set -- 0^^^128^192^224^240^248^252^254^ $(( (${#1} - ${#x})*2 )) ${x%%.*}
    x=${1%%$3*}
    echo $(( $2 + (${#x}/4) ))
}
cdr2mask ()
{
    # Number of args to shift, 255..255, first non-255 byte, zeroes
    set -- $(( 5 - ($1 / 8) )) 255 255 255 255 $(( (255 << (8 - ($1 % 8))) & 255 )) 0 0 0
    [ $1 -gt 1 ] && shift $1 || shift
    echo ${1-0}.${2-0}.${3-0}.${4-0}
}
 # examples:
mask2cdr 255.255.255.0
cdr2mask 24