Replaces a long regular expression list by matching a comma (,), left brace (), the beginning of the input string, the end of the input string, or a space. A(B|C)D matches ABD and ACD, but not AD, ABCD, ABBD, or ACCD.
![caret symbol in nx caret symbol in nx](https://i.stack.imgur.com/hAdhF.png)
Matches one of the characters or character patterns on either side of the vertical bar.
#Caret symbol in nx plus
Matches one or more sequences of the character preceding the plus sign.
![caret symbol in nx caret symbol in nx](https://res.cloudinary.com/engineering-com/image/upload/v1435761587/tips/Ordinate_Interestion_Point_ptinfm.png)
Also acts as a wildcard for matching any number of characters. Matches zero or more sequences of the character preceding the asterisk. Matches the character or null string at the end of an input string. (Precede the question mark with Ctrl-V sequence to prevent it from being interpreted as a help command.) Matches zero or one occurrence of the pattern. Matches the character or null string at the beginning of an input string. matches 0, 4, and w, but not 1, 9, or K.Matches the characters or a range of characters separated by a hyphen, within left and right square brackets. allows a period to be matched as a period Also matches (escapes) special characters. Matches the character following the backslash. t.t matches strings such as test, text, and tart.X.25 route substitute destination featureīelow the basic Cisco IOS regular expression characters and their functions.The following is a list of some of these implementations: If a regular expression can match two different parts of an input string, it will match the earliest part first.Ĭisco configurations uses regular expression pattern matching in several implementations. Pattern matching either succeeds or fails. Matching the string to the specified pattern is called pattern matching. Ken Thompson built Kleene’s notation into the editor QED as a means to match patterns in text files.Ī 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).
The SNOBOL language was an early implementation of pattern matching, but not identical to regular expressions. In the 1950s, mathematician Stephen Cole Kleene described these models using his mathematical notation called regular sets. These fields study models of computation (automata) and ways to describe and classify formal languages. The origins of regular expressions lie in automata theory and formal language theory, both of which are part of theoretical computer science.