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Regex#

\d - matches a digit or a character from 0 to 9
\s - match a whitespace symbol such a space, a tab (\t), a newline (\n), etc.
\w - w stands for word character. It matches the ASCII character [A-Za-z0-9_] including Latin alphabets, digits, and the underscore ( _ )
- Inverse Classes#
  - \D - matches any character except digits e.g., a letter.
  - \S - matches any character except whitespace e.g., a letter
  - \W - matches any character except word character e.g., non-Latin letter or space.
dot( . ) - is a special character class that matches any character except a newline.

Anchors have special meaning in regular expressions. They do not match any character. Instead, they match a position before or after characters:

^ - The caret anchor matches the beginning of the text.
$ - The dollar anchor matches the end of the text.
\b - The word boundary anchor matches the position
- The following three positions that qualify as word boundaries:
  - Before the first character in a string if the first character is a word character.
  - After the last character in a string if the last character is a word character.
  - Between two characters in a string if one is a word character and the other is not.

Quantifiers match a number of instances of a character, group, or character class in a string.

Exact count {n} - A number in curly braces {n} is the simplest quantifier. When you append it to a character or character class, it specifies how many characters or character classes you want to match.
The range {n,m} - The range matches a character or character class from n to m times.
+ - The quantifier + means one or more, which is equivalent to {1, }
? - The quantifier ? means zero or one, which is equivalent to {0,1}
* - The quantifier * means zero or more, which is equivalent to {0, }

[...] - The square brackets searches for any character in a set.
For example, [aeiou] matches any of the five characters: 'a', 'e', 'i', 'o' and 'u'. The [...] is called a set.
[a-zA-z],[0-9] - The square brackets can contain character ranges.
For example, [a-z] is a character range from a to z. And [0-9] is a digit from 0 to 9.
[ ^abc] - To negate a range, you use the excluding range like: [ ^...].
For example, [ ^0-9] matches any character except a digit. It is the same as \D

g - global flag, when you add 'g' the regular expression will search all occurences, not just the first
m - flag to enable the multiline mode.

In practice, you often combine the character classes to form a powerful match.