ip

ip addr show eth0 | grep 'inet ' | awk '{print $2}' | cut -f1 -d'/'
ip addr show

• ifconfig -a
• ip addr (ip a)
• hostname -I | awk '{print $1}'
• ip route get 1.2.3.4 | awk '{print $7}'
• (Fedora) Wifi-Settings→ click the setting icon next to the Wifi name that you are connected to → Ipv4 and Ipv6 both can be seen
• nmcli -p device show

• curl ifconfig.me
• curl -4/-6 icanhazip.com
• curl ipinfo.io/ip
• curl api.ipify.org
• curl checkip.dyndns.org
• dig +short myip.opendns.com @resolver1.opendns.com
• host myip.opendns.com resolver1.opendns.com
• curl ident.me
• curl bot.whatismyipaddress.com
• curl ipecho.net/plain

/etc/network/interfaces

allow-hotplug eth0
iface eth0 inet static
  address 192.168.1.4        # este es mi caso
  netmask 255.255.255.0
  network 192.168.1.0
  broadcast 192.168.1.255
  gateway 192.168.1.1
 
### static routing ###
# añade una ruta a la red 10.0.0.0/8 a través del Gateway 10.9.38.65
  post-up route add -net 10.0.0.0 netmask 255.0.0.0 gw 10.9.38.65
  pre-down route del -net 10.0.0.0 netmask 255.0.0.0 gw 10.9.38.65

Versiones posteriores:

/etc/dhcpdc.conf

interface eth0
static ip_address=192.168.1.141/24
static routers=192.168.1.1
static domain_name_servers=192.168.1.1

En RedHat está en /etc/sysconfig/network-scripts/ifcfg-eth?

para añadir un «IP Alias» (otra IP, vamos):

/etc/network/interfaces

auto eth0:0
iface eth0:0 inet static
  address 192.168.1.5        # este es mi caso
  netmask 255.255.255.0
  network 192.168.1.0
  broadcast 192.168.1.255
  gateway 192.168.1.1