Here are some regex exercises for practice. :D

1. Match a string that only consists of digits.

2. Match a string that is at least 5 characters long, and only consists of alphanumeric characters.

3. Match a string that is in the format of a phone number like so: ###-###-#### where each # symbol is a number.

4. Match a string that contains at least 3 vowels.

5. Match a string that contains 4 consecutive lowercase consonants.

6. Match a string that contains two words and the first letter in each word is capitalized.

7. Match a valid postal code, for example M5R 1E4 (with one space in between).

8. Match a valid postal code with all digits the same, for example M5R 5E5.

9. Match a string containing two words that are the same. Use \b to indicate
the boundaries of a word.

10. Match a string that represents time in hh:mm:ss format, where hh is hours between 01 and 12, and mm and ss represent minutes and seconds between 00 and 59. Valid examples include 01:26:18 and 11:00:39. Invalid examples include 13:01:01, 00:00:00, and 01:00:60.