A regular expression is a mode matching tool. You can create a matching mode based on specified rules and then match target objects based on the matching mode. A regular expression consists of 1 to 256 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, underline, 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 a set of symbols with special meanings which are provided to flexibly create matching modes. The following special characters are supported by PICOS:

.* Matches any single character.
* Matches 0 or more occurrences of pattern.
+ Matches 1 or more occurrences of pattern.
? Match 0 or 1 occurrences of pattern.
^ Matches the beginning of the line.
$ Matches the end of the line.
_ The _ character has special meanings in BGP regular expressions. It matches to space and comma , and AS set
delimiter { and } and AS confederation delimiter ( and ). And it also matches to the beginning of the line and
the end of the line. So _ can be used for AS value boundaries match. This character technically evaluates to
(^|[,{}()]|$).

NOTE:

Note that space is not supported, even if in a double quotation marks "".

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