convert pcregrep command in awk or sed - awk

Question

I have a multiline matching pcregrep command that I'd like to convert into an awk or sed command, because I need it on a machine where pcregrep is not available (OS X).
Original command:
ifconfig -a | pcregrep -M '^[a-z].*\n(\t[^\n]+\n)+\t[^\n]+baseTX' | grep -oE "^([a-z]+[^:]+)"
It output the name of the interface that contains the string “baseTX” (only method I found to reliably find out the name of the ethernet interface on a MacBook). In my case, “en4”.
The input text look like this:
lo0: flags=8049<UP,LOOPBACK,RUNNING,MULTICAST> mtu 16384
options=3<RXCSUM,TXCSUM>
inet6 ::1 prefixlen 128
inet 127.0.0.1 netmask 0xff000000
inet6 fe80::1%lo0 prefixlen 64 scopeid 0x1
nd6 options=1<PERFORMNUD>
gif0: flags=8010<POINTOPOINT,MULTICAST> mtu 1280
stf0: flags=0<> mtu 1280
en0: flags=8863<UP,BROADCAST,SMART,RUNNING,SIMPLEX,MULTICAST> mtu 1500
ether xx:xx:xx:xx:xx:xx
inet6 xxxx::xxxx:xxxx:xxxx:xxx%en0 prefixlen 64 scopeid 0x4
inet 10.xxx.xxx.xx netmask 0xffffff00 broadcast 10.xxx.xxx.255
inet6 xxxx:xxx:xxxx:xxxx:xxxx:xxxx:xxxx:xxxx prefixlen 128
nd6 options=1<PERFORMNUD>
media: autoselect
status: active
en5: flags=8963<UP,BROADCAST,SMART,RUNNING,PROMISC,SIMPLEX,MULTICAST> mtu 1500
options=60<TSO4,TSO6>
ether xx:xx:xx:xx:xx:xx
media: autoselect <full-duplex>
status: inactive
en6: flags=8963<UP,BROADCAST,SMART,RUNNING,PROMISC,SIMPLEX,MULTICAST> mtu 1500
options=60<TSO4,TSO6>
ether xx:xx:xx:xx:xx:xx
media: autoselect <full-duplex>
status: inactive
en4: flags=8863<UP,BROADCAST,SMART,RUNNING,SIMPLEX,MULTICAST> mtu 1500
options=4<VLAN_MTU>
ether xx:xx:xx:xx:xx:xx
inet6 xxxx::xxxx:xxxx:xxxx:xxxx%en4 prefixlen 64 scopeid 0x7
inet XX.XXX.XXX.XX netmask 0xffffff00 broadcast XX.XXX.XXX.XXX
inet6 xxxx:xxx:xxxx:xxxx:xxxx:xxxx:xxxx:xxxx prefixlen 128
nd6 options=1<PERFORMNUD>
media: autoselect (100baseTX <full-duplex>)
status: active
bridge0: flags=8863<UP,BROADCAST,SMART,RUNNING,SIMPLEX,MULTICAST> mtu 1500
options=63<RXCSUM,TXCSUM,TSO4,TSO6>
ether xx:xx:xx:xx:xx:xx
Configuration:
id 0:0:0:0:0:0 priority 0 hellotime 0 fwddelay 0
maxage 0 holdcnt 0 proto stp maxaddr 100 timeout 1200
root id 0:0:0:0:0:0 priority 0 ifcost 0 port 0
ipfilter disabled flags 0x2
member: en5 flags=3<LEARNING,DISCOVER>
ifmaxaddr 0 port 5 priority 0 path cost 0
member: en6 flags=3<LEARNING,DISCOVER>
ifmaxaddr 0 port 6 priority 0 path cost 0
nd6 options=1<PERFORMNUD>
media: <unknown type>
status: inactive
p2p0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 2304
ether xx:xx:xx:xx:xx:xx
media: autoselect
status: inactive
How can I grap “en4” with awk or sed? I tried for one hour, but I am just bad at sed and awk.

Answer 1

Assuming that spacing is consistent (leading spaces are only on non-header lines) this should work:
awk -F: '/^[[:alpha:]]/ {iface=$1; next} /baseTX/ {print iface; exit}'

Answer 2

perl:
perl -0777 -nE 'say map {/^\w+/ && $&} grep {/baseTX/} split /^(?=\w+:)/m'