In Perl, the key is to keep a copy of the previous line: 
use strict;
use warnings;

my $prev;
while (<DATA>) {
    print $prev if $prev and /Northbound to/i or /Southbound to/i;
    $prev = $_;
}

__DATA__
interface POS2/1
 bandwidth 155520
 no ip address
 no ip directed-broadcast
 no ip proxy-arp
 load-interval 30
 shutdown
 crc 16
!
interface POS2/2
 description PL000000/00000000-O, NNI southbound To Somewhere fms 1111
+1111
 no ip address
 no ip directed-broadcast
 no ip proxy-arp
 encapsulation frame-relay IETF
 no ip mroute-cache
 crc 16
 frame-relay lmi-type cisco
!
interface POS2/2.30 point-to-point
 description POS2/2.30 fr dlci=30. By VPNSC: Job Id# = 9999
 ip vrf forwarding V1234:Customer
 ip address 192.168.254.2 255.255.255.252
 no ip directed-broadcast
 snmp trap link-status
 no cdp enable
 frame-relay interface-dlci 30 IETF

[download]
Prints: 
interface POS2/2

[download]

In reply to Re: Print line before match by toolic
in thread Print line before match by ddrew78

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