CCIE or Null!

My journey to CCIE!

Using regular expressions to make troubleshooting easier.

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I’ve mentioned regular expressions throughout a few my articles over the last few years, usually as part of a configuration. However something I wanted to throw out there, is the fact you can use regular expressions with show commands. This can save quite a bit of time when bouncing between devices all day.

A few examples that I commonly use:

Let’s say you want to easily to pick out and view individual routes in the routing table or BGP table, here I used the underscore “_” regular expression to pick out only the route I wanted. This also works quite well to quickly see the default route.


Something I got tired of real quick, was checking interface errors since we all know issuing “show int” displays an awful lot of information, here I used the pipe “|” to look for multiple strings.


Let’s also say you need to quickly see the status of multiple interfaces on a chassis or stackable switch, we can use the brackets “[” “]” to look at a range of numbers, so you can easily view a particular interface across the stack or chassis, and/or even to see a range of interfaces across the stack/chassis. (I don’t have a functional stack in my lab yet but that RegEx would work across the first 2 stack members)


Now regular expressions are very powerful and there are quite a few I did not mention here. I highly recommend taking some time to go over them and see you can come up with. Feel free leave those findings in the comments below!

You can read more about the RegEx’s here.

Written by Stephen J. Occhiogrosso

February 19, 2014 at 11:22 AM

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