display Commands

Regular Expressions

A regular expression is a mode matching tool. It consists of common characters (such as letters from a to z) and special characters (called meta-characters). The regular expression is a template according to which you can search for the required string.

A regular expression provides the following functions:

• Searches for and obtains a sub-string that matches a rule in the string.
• Substitutes a string based on a certain matching rule.

The regular expression consists of common characters and special characters.

• Common characters

  Common characters are used to match themselves in a string, including all upper-case and lower-case letters, digits, punctuations, and special symbols. For example, a matches the letter "a" in "abc", 10 matches the digit "10" in "10.113.25.155", and @ matches the symbol "@" in "xxx@xxx.com".

• Special characters

  Special characters are used together with common characters to match the complex or special string combination. Table 19-2 describes special characters and their syntax.

  Table 19-2 Description of special characters

  Special Characters	Function	Example
  \	Defines an escape character, which is used to mark the next character (common or special) as the common character.	\* matches "*".
  ^	Matches the starting position of the string.	^10 matches "10.10.10.1" instead of "172.20.10.1".
  $	Matches the ending position of the string.	1$ matches "10.10.10.1" instead of "10.10.10.2".
  *	Matches the preceding element zero or more times.	10* matches "1", "10", "100", "1000", and so on. (10)* matches "null", "10", "1010", "101010", and so on.
  +	Matches the preceding element one or more times.	10+ matches "10", "100", "1000", and so on. (10)+ matches "10", "1010", "101010", and so on.
  ?	Matches the preceding element zero or one time. NOTE: Huawei datacom devices do not support regular expressions with ?. When regular expressions with ? are entered on Huawei datacom devices, helpful information is provided.	10? matches "1" or "10". (10)? matches "null" or "10".
  .	Matches any single character.	0.0 matches "0x0", "020", and so on. .oo. matches "book", "look", "tool", and so on.
  ()	Defines a subexpression, which can be null. Both the expression and the subexpression should be matched.	100(200)+ matches "100200", "100200200", and so on.
  x|y	Matches x or y.	100|200 matches "100" or "200". 1(2|3)4 matches "124" or "134", instead of "1234", "14", "1224", and "1334".
  [xyz]	Matches any single character in the regular expression.	[123] matches the character 2 in "255".
  [^xyz]	Matches any character that is not in the regular expression.	[^123] matches any character except for "1", "2", and "3".
  [a-z]	Matches any character within the specified range.	[0-9] matches any character ranging from 0 to 9.
  [^a-z]	Matches any character beyond the specified range.	[^0-9] matches all non-numeric characters.
  _	Matches a comma ",", left brace "{", right brace "}", left parenthesis "(", and right parenthesis ")". Matches the starting position of the input string. Matches the ending position of the input string. Matches a space.	_2008_ matches "space 2008 space", ",2008,", "{2008}", "(2008)", "{2008)", and "(2008}". _2008 matches "space 2008", ",2008", "{2008","(2008". _2008 matches "2008 space", "2008,", "2008{","2008)".

  Unless otherwise specified, all the characters in the preceding table must be printable characters.

• Degeneration of special characters

  Certain special characters, when placed at certain positions in a regular expression, degenerate to common characters.

  • The special characters following "\" match special characters themselves.
  • The special characters "*", "+", and "?" are placed at the starting position of the regular expression. For example, +45 matches "+45" and abc(*def) matches "abc*def".
  • The special character "^" is placed at any position except for the start of the regular expression. For example, abc^ matches "abc^".
  • The special character "$" is placed at any position except for the end of the regular expression. For example, 12$2 matches "12$2".
  • A right parenthesis ")" or right bracket "]" is not paired with a corresponding left parenthesis "(" or bracket "[". For example, abc) matches "abc)" and 0-9] matches "0-9]".

Unless otherwise specified, degeneration rules also apply when the preceding regular expressions are subexpressions within parentheses.

• Combination of common and special characters

  In actual usage, regular expressions combine multiple common and special characters to match certain strings.

Specifying a Filtering Mode in a Command

• The device uses a regular expression to implement the pipe character filtering function. A display command supports the pipe character only when there is excessive output information.
• When filtering conditions are set to query output information, the first line of the command output starts with the entire regular expression but not the string to be filtered.

Some commands can carry the keyword | count to display the number of matching entries. The keyword | count can be used together with other keyword.

Three filtering modes are provided for commands that support regular expressions.

• | begin regular-expression: displays all the lines beginning with the line that matches the regular expression.

  Filter the character strings to be entered until the specified case-sensitive character string is displayed. All the character strings following this specified character string are displayed on the screen.

• | exclude regular-expression: displays all the lines that do not match the regular expression.

  If the character strings to be entered do not contain the specified case-sensitive character string, they are displayed on the screen. Otherwise, they are filtered.

• | include regular-expression: displays all the lines that match the regular expression.

  If the character strings to be entered contain the specified case-sensitive character string, they are displayed on the screen. Otherwise, they are filtered.

The value of regular-expression is a string of 1 to 255 characters. If regular-expression contains special characters, to interpret them literally, add a backslash "\" before the characters.

The following examples describe how to specify a filter mode in a command.

Example 1: Run the display interface brief command to display all the lines that do not match the regular expression GigabitEthernet|Wlan-Dbss|Tunnel. GigabitEthernet|Wlan-Dbss|Tunnel matches GigabitEthernet, Wlan-Dbss or Tunnel.

<AC> display interface brief | exclude GigabitEthernet|Wlan-Dbss|Tunnel
PHY: Physical                                                                    
*down: administratively down                                                     
(l): loopback                                                                    
(s): spoofing                                                                    
(b): BFD down                                                                    
(e): ETHOAM down                                                                 
(d): Dampening Suppressed                                                        
InUti/OutUti: input utility/output utility                                       
Interface                   PHY   Protocol InUti OutUti   inErrors  outErrors    
Eth-Trunk1                  down  down        0%     0%          0          0    
LoopBack0                   up    up(s)       0%     0%          0          0    
MEth0/0/1                   up    up          0%     0%          0          0    
NULL0                       up    up(s)       0%     0%          0          0    
Vlanif1                     up    down        --     --          0          0    
Vlanif2                     down  down        --     --          0          0    
Vlanif3                     down  down        --     --          0          0    
Vlanif4                     down  down        --     --          0          0    
Vlanif10                    up    up          --     --          0          0    
Vlanif100                   down  down        --     --          0          0    
Vlanif101                   down  down        --     --          0          0    
Vlanif102                   down  down        --     --          0          0    
Vlanif400                   up    up          --     --          0          0    
Wlan-Ess0                   down  down        0%     0%          0          0    
Wlan-Ess1                   down  down        0%     0%          0          0    
Wlan-Ess10                  up    up          0%     0%          0          0    
Wlan-Ess100                 down  down        0%     0%          0          0   

Example 2: Run the display current-configuration command to display all the lines that match the regular expression vlan.

<AC> display current-configuration | include vlan
vlan batch 10 400
 port trunk allow-pass vlan 10
 port trunk pvid vlan 10

The preceding information is used for reference only.