Monday, September 27, 2010

Counting Regex Matches on Catalyst Switches

As an old-time Unix/Linux guy, I’ve been wanting the IOS equivalent of the “wc -l” command for oh, about a million years now. Juniper has had this in JunOS for quite some time, via their “count” command. In Unix/Linux shell environments, “wc -l” counts the number of lines in the input. This is very useful for things like counting the number of unused ports on a switch. Until recently, I was stuck with using SSH one-liners to pipe IOS commands through a shell filter, like this:

$ ssh 'sh int status | i not|disa' | wc -l

In English: this executes the command “show interface status | include not|disa” via SSH on the remote device, which returns all the lines that are in either the “notconnected” or “disabled” status. Then it feeds those lines to the “wc -l” command, which counts the lines.

A couple of months ago, however, I noticed that recent versions of IOS for the Catalyst access switches (3560/3750, and probably the 2960--I haven’t tested the latter) have a “count” filter:

Switch#sh int status | count ?
LINE Regular Expression

Switch#sh int status | count not|disa
Number of lines which match regexp = 19

Anyway, nothing particularly groundbreaking here, just a nice feature that’s long overdue--I hope it gets ported into other IOS images as well.