Bash script match ipv4 addresses with regex variable - bash

Question

Trying to get only the lines with ipv4 addresses in the $networks variable.
#!/bin/bash
ivp4_pattern='/^([0-9]{1,3}\.){3}[0-9]{1,3}(\/([0-9]|[1-2][0-9]|3[0-2]))?$/igm'
networks=$(ip addr | grep "inet" | awk '{print $2}')
while read -r line;
do
echo "$line"
done <<< "$networks"
echo "$ivp4_pattern"
echo "$networks" | grep "$ivp4_pattern"
Output:
[jonathan#localhost ~]$ ./script.sh
127.0.0.1/8
::1/128
172.16.155.128/24
fe80::da84:977a:d654:7716/64
/^([0-9]{1,3}\.){3}[0-9]{1,3}(\/([0-9]|[1-2][0-9]|3[0-2]))?$/igm
Tried removing the / and with -E...
#!/bin/bash
ivp4_pattern="'^([0-9]{1,3}\.){3}[0-9]{1,3}(\/([0-9]|[1-2][0-9]|3[0-2]))?$'"
networks=$(ip addr | grep "inet" | awk '{print $2}')
while read -r line;
do
echo "$line"
done <<< "$networks"
echo $ivp4_pattern
echo $networks | grep -E $ivp4_pattern
Also tried loop through networks line by line and taking the regex out of the variable...
#!/bin/bash
networks=$(ip addr | grep "inet" | awk '{print $2}')
while read -r line;
do
echo "$line"
done <<< "$networks"
while read -r line;
do
echo $line
echo $line | grep '^([0-9]{1,3}\.){3}[0-9]{1,3}(\/([0-9]|[1-2][0-9]|3[0-2]))?$'
done <<< "$networks"
I got it working adding -E to grep without regex in variable...but why is it working? It doesn't like the regex being in a variable?
#!/bin/bash
networks=$(ip addr | grep "inet" | awk '{print $2}')
while read -r line;
do
echo "$line"
done <<< "$networks"
while read -r line;
do
# echo $line
echo $line | grep -E '^([0-9]{1,3}\.){3}[0-9]{1,3}(\/([0-9]|[1-2][0-9]|3[0-2]))?$'
done <<< "$networks"
~

Answer 1

As a bash solution, how about:
ipv4_pattern="([0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3})"
ip addr | while read -r line; do
if [[ $line =~ inet\ $ipv4_pattern ]]; then
echo "${BASH_REMATCH[1]}"
fi
done
Note that the while loop above is invoked in the child process and
variables assigned here are inaccessible from the parent.
In such a case, please make use of a process substitution as;
ipv4_pattern="([0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3})"
while read -r line; do
if [[ $line =~ inet\ $ipv4_pattern ]]; then
echo "${BASH_REMATCH[1]}"
# do some assignments here as ip_list+=("${BASH_REMATCH[1]}")
fi
done < <(ip addr)
Hope this helps.

Answer 2

If you want to list only IPv4 addresses, how about this?
The first ...
#!/bin/bash
#
# ip addr : list IP info.
# grep "inet " : Only for IPv4. IPv6 addresses are listed up with "inet6".
# awk '{print $2}': Extract IPv4 adress
ipaddrs=$(ip addr | grep "inet " | awk '{print $2}')
while read -r ipaddr
do
echo $(cut -d"/" -f1 <<< ${ipaddr})
done <<< "${ipaddrs}"
exit 0
The Second is ...
#!/bin/bash
#
# ip addr : list IP info.
# grep "inet " : Only for IPv4. IPv6 addresses are listed up with "inet6".
ipaddrs=$(ip addr | grep "inet ")
while read -r ipaddr
do
# sample: inet 100.52.62.173/24 brd 100.52.62.255 scope global bond1
ipv4_cidr=$(cut -d" " -f2 <<< ${ipaddr})
ipv4=$(cut -d"/" -f1 <<< ${ipv4_cidr})
netmask=$(cut -d"/" -f2 <<< ${ipv4_cidr})
brdcast=$(cut -d" " -f4 <<< ${ipaddr})
echo "----------------------------"
echo "============================"
echo "ip addr : ${ipaddr}"
echo "----------------------------"
echo "IP Address: ${ipv4}"
echo "Netmask : ${netmask}"
echo "Broadcast : ${brdcast}"
done <<< "${ipaddrs}"
exit 0
The third is ...
#!/bin/bash
#
# ip addr : list IP info.
# grep "inet " : Only for IPv4. IPv6 addresses are listed up with "inet6".
ipaddrs=$(ip addr | grep "inet ")
while IFS=" " read -ra ipaddr
do
# If a first line is "inet 100.52.62.173/24 brd 100.52.62.255 scope global bond1"
# 1. ipadddr is (inet 100.52.62.173/24 brd 100.52.62.255 scope global bond1)
# A second is cidr.
IFS="/" read -ra ipv4_cidr <<< "${ipaddr[1]}"
# 2. ipv4_cidr is ("100.52.62.173" "24")
ipv4="${ipv4_cidr[0]}"
netmask="${ipv4_cidr[1]}"
# A fourth is 'broadcast'.
brdcast="${ipaddr[3]}"
echo "----------------------------"
echo "============================"
echo "ip addr : ${ipaddr[#]}"
echo "----------------------------"
echo "IP Address: ${ipv4}"
echo "Netmask : ${netmask}"
echo "Broadcast : ${brdcast}"
done <<< "${ipaddrs}"
exit 0