Php get first day of month

- Php get first day of month from date
- Php get first day of current month
- Php get first day of last month
- Php get first day of next month
- Php get first day of previous month
- Php carbon get first day of month
- Php get timestamp of first day of month
- Php datetime get first day of current month
- Php carbon first day of month
- Php modify first day of month