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Calculating network addresses in tthe shell script
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#!/bin/sh | |
# converts IPv4 as "A.B.C.D" to integer | |
# ip4_to_int 192.168.0.1 | |
# => 3232235521 | |
ip4_to_int() { | |
IFS=. read -r i j k l <<EOF | |
$1 | |
EOF | |
echo $(( (i << 24) + (j << 16) + (k << 8) + l )) | |
} | |
# converts interger to IPv4 as "A.B.C.D" | |
# | |
# int_to_ip4 3232235521 | |
# => 192.168.0.1 | |
int_to_ip4() { | |
echo "$(( ($1 >> 24) % 256 )).$(( ($1 >> 16) % 256 )).$(( ($1 >> 8) % 256 )).$(( $1 % 256 ))" | |
} | |
# returns the ip part of an CIDR | |
# | |
# cidr_ip "172.16.0.10/22" | |
# => 172.16.0.10 | |
cidr_ip() { | |
IFS=/ read -r ip _ <<EOF | |
$1 | |
EOF | |
echo $ip | |
} | |
# returns the prefix part of an CIDR | |
# | |
# cidr_prefix "172.16.0.10/22" | |
# => 22 | |
cidr_prefix() { | |
IFS=/ read -r _ prefix <<EOF | |
$1 | |
EOF | |
echo $prefix | |
} | |
# returns net mask in numberic from prefix size | |
# | |
# netmask_of_prefix 8 | |
# => 4278190080 | |
netmask_of_prefix() { | |
echo $((4294967295 ^ (1 << (32 - $1)) - 1)) | |
} | |
# returns default gateway address (network address + 1) from CIDR | |
cidr_default_gw() { | |
ip=$(ip4_to_int $(cidr_ip $1)) | |
prefix=$(cidr_prefix $1) | |
netmask=$(netmask_of_prefix $prefix) | |
gw=$((ip & netmask + 1)) | |
int_to_ip4 $gw | |
} | |
# returns default gateway address (broadcast address - 1) from CIDR | |
cidr_default_gw_2() { | |
ip=$(ip4_to_int $(cidr_ip $1)) | |
prefix=$(cidr_prefix $1) | |
netmask=$(netmask_of_prefix $prefix) | |
broadcast=$(((4294967295 - netmask) | ip)) | |
int_to_ip4 $((broadcast - 1)) | |
} | |
cidr_default_gw 192.168.10.1/24 | |
# => 192.168.10.1 | |
cidr_default_gw 192.168.10.1/16 | |
# => 192.168.0.1 | |
cidr_default_gw 172.17.18.19/20 | |
# => 172.17.16.1 | |
cidr_default_gw_2 192.168.10.1/24 | |
# => 192.168.10.254 | |
cidr_default_gw_2 192.168.10.1/16 | |
# => 192.168.255.254 | |
cidr_default_gw_2 172.17.18.19/20 | |
# => 172.17.31.254 |
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Very nice 🌚