Using regular expressions with the ‘Show’ command
Do you remember the “Cisco regular expressions” tutorial? A regular expression is entered as part of a command and is a pattern made up of symbols, letters, and numbers that represent an input string for matching (or sometimes not matching). Matching the string to the specified pattern is called pattern matching. Pattern matching either succeeds or fails. If a regular expression can match two different parts of an input string, it will match the earliest part first.
In this tutorial, I will explain how to use the ‘show’ command with the regular expression.
Below some examples:
To check exactly an IP address use the backslash (\) before the dot (.) to remove the special meaning of the dot (.) character and the underscore (_) to check the space before/after the IP address. For example, to find the ip address 10.0.0.1 in the running configuration, use the command
show run | i _10\.0\.0\.1_
and not the command (it can match 10.0.0.1, 220.127.116.11, 10.1.1.11, …)
show run | i 10.0.0.1
To see all the VRF route:
sh ip route vrf *
and to eliminate the lines:
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2 E1 - OSPF external type 1, E2 - OSPF external type 2 i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2 ia - IS-IS inter area, * - candidate default, U - per-user static route o - ODR, P - periodic downloaded static route Gateway of last resort is not set
try this regular expression (it is true when the line contains one number, one dot (.) or the word ‘Routing’:
sh ip route vrf * | i (([0-9]\.)|Routing)
To see all ‘administratively down’ fastethernet interfaces in the module #1 (it is true when the line starts with the character ‘F’ followed by ‘t1/’ and contains the word ‘administr’:
sh ip inter brie | i ^F.*t1/.*administr
To see all CDP entry:
sh cdp entry *
and to view only the device name and the IP address (it is true when the line starts with the string ‘Device’ or contains the string ‘IP address’:
sh cdp entry * | i (^Device|IP address)
To search a mac address that starts with ‘c800’:
sh mac-address-table | i ^c800\.
… and to find a mac ddress that end with ‘0000’:
sh mac-address-table | i (.*)\.(.*)\.0000
Below a good example of the RegEx with the ‘show’ command. The commands used are:
- show run | i _10\.0\.0\.1_
- sh ip inter brie | i ^F.*t1/.*administr
- sh mac-address-table | i ^c800\.
- sh mac-address-table | i (.*)\.(.*)\.0000
To better understand the example in the video, check the partial running-configuration:
hostname Ciscozine ! ! interface Loopback0 ip address 10.0.0.1 255.255.255.0 ! interface Loopback1 ip address 10.0.10.1 255.255.255.0 ! interface Loopback2 ip address 10.10.0.1 255.255.255.0 ! interface Loopback3 ip address 10.10.10.1 255.255.255.0 ! interface Loopback4 ip address 18.104.22.168 255.255.255.0 ! interface Loopback5 ip address 22.214.171.124 255.255.255.0 ! interface FastEthernet0/0 no ip address shutdown duplex auto speed auto ! interface FastEthernet0/1 no ip address shutdown duplex auto speed auto ! interface FastEthernet1/0 shutdown ! interface FastEthernet1/1 shutdown ! interface FastEthernet1/2 shutdown ! interface FastEthernet1/3 shutdown ! interface FastEthernet1/4 shutdown ! interface FastEthernet1/5 shutdown ! interface FastEthernet1/6 shutdown ! interface FastEthernet1/7 shutdown ! interface FastEthernet1/8 ! interface FastEthernet1/9 ! interface FastEthernet1/10 ! interface FastEthernet1/11 ! interface FastEthernet1/12 ! interface FastEthernet1/13 ! interface FastEthernet1/14 ! interface FastEthernet1/15 !
and the show ip inter brief | exclude Vlan:
Ciscozine#sh ip interface brie | exclude Vla Interface IP-Address OK? Method Status Protocol FastEthernet0/0 unassigned YES NVRAM administratively down down FastEthernet0/1 unassigned YES NVRAM administratively down down FastEthernet1/0 unassigned YES unset administratively down down FastEthernet1/1 unassigned YES unset administratively down down FastEthernet1/2 unassigned YES unset administratively down down FastEthernet1/3 unassigned YES unset administratively down down FastEthernet1/4 unassigned YES unset administratively down down FastEthernet1/5 unassigned YES unset administratively down down FastEthernet1/6 unassigned YES unset administratively down down FastEthernet1/7 unassigned YES unset administratively down down FastEthernet1/8 unassigned YES unset up down FastEthernet1/9 unassigned YES unset up down FastEthernet1/10 unassigned YES unset up down FastEthernet1/11 unassigned YES unset up down FastEthernet1/12 unassigned YES unset up down FastEthernet1/13 unassigned YES unset up down FastEthernet1/14 unassigned YES unset up down FastEthernet1/15 unassigned YES unset up down Loopback0 10.0.0.1 YES manual up up Loopback1 10.0.10.1 YES manual up up Loopback2 10.10.0.1 YES manual up up Loopback3 10.10.10.1 YES manual up up Loopback4 126.96.36.199 YES manual up up Loopback5 188.8.131.52 YES manual up up
Remember: To negate an expression use ‘exclude’ instead of the ‘include’!
Remember: The RegEx ‘show’ can be saved with the alias feature! For instance, if you would create a shortcut to the command
sh ip route vrf * | i (([0-9]\.)|Routing)
define it in global configuration:
alias exec allvrfroute sh ip route vrf * | i (([0-9]\.)|Routing)
and use it (allvrfroute) in priviledge mode or (do allvrfroute) in global configuration!
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