+##converts subnet mask to prefix
+##params: subnet mask
+function prefix2mask {
+ # 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}
+}
+