How do I store network information in variables in BASH?

Question

I am writing a bash script and need to store some primitive network information in separate variables. For example, mac address and IP address in separate variables, for example

IPADDRESS=$(some_command)
MACADDRESS=$(some_other_command)
echo "$IPADDRESS has mac address $MACADDRESS"

This is a simplified example, since I AM NOT going to be reading this directly, but rather passing to a proprietary program as /bin/proprietary_program $IPADDRESS $MACADDRESS.

How do I get just the MAC address as a string and the IP address as a string in Linux? I prefer to use the ip command where possible.

Thanks for the link. The systems this runs on should only have the one interface, but in the event that there's more than one I will ask the user to enter the interface name they want to use — Anon Ymous, Nov 30 '20 at 16:41
Which IP address? IPv4? IPv6? Both? Local network? External network? Presumably you don't want the `127.0.0.1` IP, right? Can you post the output of `ip addr` and tell us what you want to capture from it? That is, assuming you are using a Linux variant. What OS does this need to work on? — terdon, Nov 30 '20 at 18:02
I had wanted to capture the output from `ip addr` for link/ether, although I seem to have managed this by some weird combination of grep and cut via `MACADDR=$(ip -4 -o link list $IFACE | grep -o -E 'link/ether.*' | cut -d ' ' -f 2)`; I can do similar for ip address and add a `cut -d '/' -f 1` to cut off the /16 after the IP. — Anon Ymous, Dec 02 '20 at 02:33

score 0 · Answer 1 · answered Nov 30 '20 at 17:57

Since I didn't see any examples using nmcli (NetworkManager), I'll add them here:

nmcli -f IP4.ADDRESS device show your_nic (returns all IPv4 addresses)
nmcli -f IP6.ADDRESS device show your_nic (returns all IPv6 addresses)
nmcli -f GENERAL.HWADDR device show your_nic (returns MAC address)

Stewart · Answer 2 · 2020-11-30T18:22:32.487

You could parse the output of ip address: Mine looks like this (I've added extra IP addresses to show it can be done):

$ ip address
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host 
       valid_lft forever preferred_lft forever
2: enp10s0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc mq state DOWN group default qlen 1000
    link/ether f0:79:59:dc:c4:bf brd ff:ff:ff:ff:ff:ff
3: eno1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
    link/ether f0:79:59:dc:c3:75 brd ff:ff:ff:ff:ff:ff
    altname enp0s25
    inet 192.168.1.100/24 brd 192.168.1.255 scope global noprefixroute eno1
       valid_lft forever preferred_lft forever
    inet 129.168.1.101/24 scope global eno1
       valid_lft forever preferred_lft forever
    inet6 fe80::f279:59ff:fedc:c375/64 scope link noprefixroute 
       valid_lft forever preferred_lft forever

If we grep a regex for the address we could end up with a list of IPv4 addresses.

$ IPV4=$(ip address | grep -oE '[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\/[0-9]{1,2}' )

$ echo $IPV4
127.0.0.1/8 192.168.1.100/24 129.168.1.101/24

$ for i in $IPV4; do echo $i; done
127.0.0.1/8
192.168.1.100/24
129.168.1.101/24

You'd just need to write a regex for IPv6 (if desired) and MAC to round it out.

How do I store network information in variables in BASH?

2 Answers2