# REGEX in CISCO iOS, iOS XE #

[benahmeddaho_MOURAD]

Hi,

REGULAR EXPRESSION, a filtring tool based on ::
Special characters, Characters classes, Sets, Groups, Flags.
are all these ASPECTS availible in cisco iOS, iOS XE ?
is there other unknown characters  like underscore "_" ?
Best Regards!

[Giuseppe Larosa]

Hello,

yes regular expressions are available in IOS, IOS XE and IOS XR and NX-OS.

There are  two main applications for regular expresssion in IOS:

a)  Filtering BGP advertisements using regular expressions applied to the AS path attribute seen as a sequence of characters

see

https://www.cisco.com/c/en/us/support/docs/ip/border-gateway-protocol-bgp/13754-26.html?dtid=osscdc000283

b) using regular expressions in show commands to filter show output.

https://learningnetwork.cisco.com/s/question/0D53i00000KssVx/regular-expression-in-cisco-show-commands?dtid=osscdc000283

Hope to help

Giuseppe

[benahmeddaho_MOURAD]

Hi,

i'm using regex to filter show commands this time !. it works almost fine, just for some cases ::

* the digits specification \d does not work
* how to escape characters  \.
* how to use ?=non-greedy as it is considered as help on cisco iOS
* is it possible to provide an underscore "_" exemples !

best regards!

[Giuseppe Larosa]

Hello,

in order to make the regex to search for a special character "literally" the character has to have a \ before

show ip int br  | inc   gigabitethernet0/0/0\.*

should show all subinterfaces of gigabitethernet0/0/0.

This trick should work also for '_' underscore to match it literally try to use \_

Hope to help

Giuseppe

[Leo Laohoo]

Please be very, very careful when dealing with IOS-XE and REGEX, particularly the "pipe".  This is due to CSCvo06817.

[benahmeddaho_MOURAD]

Hi,

using grep after the terminal shell command, does is offer more advantages or it's the same as |Pipe include ...

best regards!

[Leo Laohoo]

"grep" option only works for Nexus OS.  The bug I've pointed out is for IOS-XE.