mtcna, ccna in you signature and you do not know export command?
[jarda@RB2011UAS-2HnD] /interface ethernet> export
# mar/07/2015 12:33:19 by RouterOS 6.27
# software id = xxxx-xxxx
#
/interface ethernet
set [ find default-name=ether1 ] comment=WAN l2mtu=1600 name=ether1GW
Do you know print detail command?
[jarda@RB2011UAS-2HnD] /interface ethernet> print detail
Flags: X - disabled, R - running, S - slave
0 R ;;; WAN
name="ether1GW" default-name="ether1" mtu=1500 l2mtu=1600 mac-address=D4:CA:6D:8D:A3:08 orig-mac-address=D4:CA:6D:8D:A3:08 arp=enabled
auto-negotiation=yes advertise=10M-half,10M-full,100M-half,100M-full,1000M-half,1000M-full full-duplex=yes tx-flow-control=off
rx-flow-control=off speed=100Mbps master-port=none bandwidth=unlimited/unlimited switch=switch1