. single character

* the preceding character matches 0 or more times

+ the preceding character matches 1 or more times

? the preceding character matches 0 or 1 times only

{n} the preceding character matches n number of times

{n, m} the preceding character matches at least n times, and up to m number of times

^ matches the beginning of the line

$ matches the end of the line

() concatenate several regex

| OR operator

[abc] the character is one of the characters included in the square brakets

[a-d] the character is within the range of a to d, thus matching a, b, c, d.

[^abc] the character is not one of the characters included in the square brakets

[a-zA-Z] it matches any letter equivalent: \w
[0-9] it matches any digit equivalent: \d

' ' space equivalent: \s

' ' tab equivalent: \t