5.Регулярни изрази

Регулярни изрази

Регулярен израз – последователност от символи, които формират някаква шаблон, по който се търси

[character_group] – matches any single character in character_group
[^] - negation
[first-last] – character range: matches any single character in the range from first to last (according to the ASCII table)
\w – matches any word character (a-z, A-Z, 0-9, _)
\W - matches any non-word character – the opposite to \w
\s – matches any whitespace character (\r\n, \t, ‘ ‘)
\S – matches any non-whitespace character
\d – matches any digit character
\D – matches any non-digit character

* - matches the previous element zero or more times (as many times as possible)
+ - matches the previous element one or more times (as many times as possible)
? - matches the previous element zero or one time
+? – matches between one and unlimited times (as few times as possible) – lazy
*? – matches between zero and unlimited times (as few times as possible) – lazy

{n} - matches the previous element exactly n times
{n,} - matches the previous element at least n times
{n,m}- matches the previous element at least n times, but no more than m times

^ - the match must start at the beginning of the string or line
$ - the match must occur at the end of the string or before \n

\b – the match must occur on a boundary between a \w(alphanumeric) and a \W(non-alphanumeric) character
\B – the match must not occur on a boundary between a \w(alphanumeric) and a \W(non-alphanumeric) character


(subexpression) – captures the matched subexpression and assigns it a number
(?<name>subexpression) – captures the matched subexpression into a named group
(?:subexpression) – defines a non-capturing group
. – matches any character except new line

var regex = new Regex(string pattern);
regex.Match(string text) – returns the first match that corresponds to the pattern
regex.Matches(string text) – returns a collection of matching strings that correspond to the pattern
regex.Replace(string text, string replacement) – replaces all strings that match the pattern with the provided replacement

!!  look-behinds are more limited than look-aheads, because they do not support quantifiers of varying size such as “*”, “?”, “+”

(не работи в C#) The escape sequence \K is similar to a look-behind assertion because it causes any previously-matched characters to be omitted from the final matched string. For example, foo\Kbar matches "foobar" but reports that it has matched "bar".