A list of commands you can use to filter output on a Cisco router:

show run | include <word>
show run | interface <interface>
show run | begin <word>
show run | section include <word>

The "section" command is my newest discovery. For example, if I want to see the configuration of ALL FastEthernet interfaces on my lab router, I could type:

PE1-T1#sh run | section include FastEthernet
interface FastEthernet1/0
description connection to PE1 Internet Router
ip address 51.88.99.2 255.255.255.252
speed 100
full-duplex
interface FastEthernet1/1
no ip address
shutdown
duplex auto
speed auto
interface FastEthernet2/0
no ip address
shutdown
duplex auto
speed auto
interface FastEthernet2/1
ip address 10.7.255.100 255.255.0.0
ip nat outside
ip virtual-reassembly
duplex auto
speed auto
interface FastEthernet3/0
no ip address
shutdown
duplex auto
speed auto
interface FastEthernet3/1
no ip address
shutdown
duplex auto
speed auto

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