Using the Pipe in IOS

A lot of IOS commands give you a lot of information. Most of the time, though, it’s way too much information, and it sure would be nice to do some grep-like stuff on the output, right? Well, just like on Linux, you can use the pipe (|) to do such. That’s not a butt cheek, by the way.

The most useful function is the include directive. This is the equivalent of just plain grep on Linux, and will show you only lines that match a string that you give it. Say that you want to find what ports on your switch are down, but don’t want to grind through all the lines of a show ip interface brief. If you just pipe it to the include command followed by the word “down”, you’ll see something like this.

Switch#show ip interface brief | include down
GigabitEthernet0/4 unassigned YES unset down down
GigabitEthernet0/7 unassigned YES unset down down
GigabitEthernet0/17 unassigned YES unset down down
GigabitEthernet0/18 unassigned YES unset down down
GigabitEthernet0/19 unassigned YES unset down down
GigabitEthernet0/20 unassigned YES unset down down

You can also use the exclude directive, which is the same as a grep -v on Linux. I hope you figured out that this gives you all lines that don’t match the word, so, let’s use the exclude directive to found out what ports are down. How about we just ignore the lines that are up.

Switch#show ip interface brief | exclude up
Interface IP-Address OK? Method Status Protocol
GigabitEthernet0/4 unassigned YES unset down down
GigabitEthernet0/7 unassigned YES unset down down
GigabitEthernet0/17 unassigned YES unset down down
GigabitEthernet0/18 unassigned YES unset down down
GigabitEthernet0/19 unassigned YES unset down down
GigabitEthernet0/20 unassigned YES unset down down

Well, this won’t exactly give you all the ports that are down. What if the port is up/down?

What else can you use with the pipe? What if you want to look at the configurations of all the ports or interfaces on a box but don’t want to go through the config hitting the spacebar over and over. If you use the begin command, you’ll see the output beginning from the first match, so, using the string interface will show you the config starting at the first interface.

Switch#show running-config | begin interface
interface GigabitEthernet0/1
description Server
switchport access vlan 4
switchport mode access
spanning-tree portfast

Another good one is the section command. It’s usually used on the output of show running-config and shows you sections of the config that match your string. Huh? If you want to see the BGP section of the configuration, you can do something like thing just to see that part of the configuration.

Router#show running-config | section bgp
router bgp 1
neighbor 1.1.1.1 remote-as 65000
neighbor 1.1.1.1 version 4

There are a few other commands for use with the pipe, so explore on your own. You might also want to check out regular expressions on the Cisco IOS if you want to match more than just simple text.

Aaron Conaway

I shake my head around sometimes and see what falls out. That's what lands on these pages. If you have any questions, the best way to contact me is through Twitter at @aconaway.

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