[ ] –> Brackets. They enclose a list of characters that represent a single character in the expression.
Inside the brackets, one can specify:
-–> For Ranges
^–> For negation
.–> Period. Matches a single character
()–> Parenthesis. Used to enclose an expression
|–> Or
Positions:
^ Marks the beggining of the line
$ Marks the end of the line
/< Marks the beggining of a word
/> Marks the end of a word
Repetition Operators:
| Operator | Description |
|---|---|
| ? | Optional and matched at most once |
| * | Zero or more times |
| + | One or more times |
| {n} | n times. |
| {n,} | n or more times. |
| {n,m} | At least n times, but not more than m times |
Examples:
t[a-z]x | matches | tux |
| doesn’t match | tUx | |
[^w]in | matches | lin |
| doesn’t match | win | |
t.x | matches | tux |
| doesn’t match | tuux | |
(t.x|m.x) | matches | tux, mux |
^t.x | matches | tux rules |
| doesn’t match | rules tux | |
tu{2}x | matches | tuux |
| doesn’t match | tux | |
^.{2,15}$ | Between 2 and 15 characters | |
^[0-9] | Starts with a number | |
[^[:alnum:]] | Contains special characters |