Regular Expressions|

• [abc] will match a, b, and c (every occurrence of each letter)
• [abc]zz (or) [a-c]zz will match azz, bzz, and czz.
• [a-cx-z]zz will match azz, bzz, czz, xzz, yzz, and zzz.
• [a-zA-Z] will match any single letter (lowercase or uppercase).

Exclude character:

• [^k]ing will match ring, sing, $ing, but not king.
• [^a-c]at fat and hat, but not bat or cat.
• [a-cx-z]zz will match azz, bzz, czz, xzz, yzz, and zzz.
• [a-zA-Z] will match any single letter (lowercase or uppercase).

Wildcards:

• a.c will match aac, abc, a0c, a!c, and so on. (use \ to escape)
• a.*c will match everything between first occurrence of a and last occurrence of c

Optional characters:

• abc? will match ab and abc, since c is optional.

Metacharacters:

• \d matches a digit 0-9
• \D matches a non-digit, like A or @ etc.
• \w matches an alphanumeric character, like a or 4 etc. (NOTE: _ is included in \w not in \W)
• \W matches a non-alphanumeric character, like ! or # (A.K.A Special Characters)
• \s matches any whitespace characters. (spaces, tabs, and line breaks)
• \S matches everything else except whitespace characters. (alphanumeric characters and symbols)

Repetitions:

• z{2} will match exactly zz.
• {12} exactly 12 times.
• {1,5} 1 to 5 times.
• {2,} 2 or more times.
• * 0 or more times.
• + 1 or more times.

• ^ Starts with
  ex: ^abc search for a line that starts with abc.


• $ Ends with
  ex: abc$ search for a line that ends with abc.

NOTE: The ^ caret symbol is used to exclude a charset when enclosed in [square brackets], but when it's used without square brackets it specifies the beginning of a word or a line.

Anything enclosed between () are called groups. They capture the text matched by the regex inside them into a numbered group that can be reused with a numbered backreference.

ex: during the (day|night) will match both of these sentences: 'during the day' and 'during the night'.

ex: (no){5} will match the sentence 'nonononono'.