| Regular expression: | ||
| Test string: | ||
| ^ | start of line | |
| $ | end of line | |
| . | any symbol | alphabet, Σ |
| | | either | Union, ∪ |
| * | zero or more copies | Kleene's star (...)* |
| + | at least one copy | (...)+ |
| abba | accepts any string with abba in it |
| ^abba$ | accepts only one string, abba |
| ^(10)+1$ | accepts strings of form 10101...01 |
| ^(1|0)*1$ | accepts odd binary numbers |