Example 1: strtime format
# exemple
print(date.strftime("%Y/%m/%d")) #2020/12/31
# all format codes
# %a | Weekday as locale’s abbreviated name. | Sun, Mon, …, Sat (en_US)
# ---|--------------------------------------------------------------------
# %A | Weekday as locale’s full name. | Sunday, Monday, …, Saturday
# ------------------------------------------------------------------------
# %w | Weekday as a decimal number, | 0, 1, ...,6
# | where 0 is Sunday and 6 is Saturday. |
# ------------------------------------------------------------------------
# %d | Day of the month as a zero-padded | 01, 02, …, 31
# | decimal number. |
# ------------------------------------------------------------------------
# %b | Month as locale’s abbreviated name. | Jan, Feb, …, Dec
# ------------------------------------------------------------------------
# %B | Month as locale’s full name. | January, February, …, December
# ------------------------------------------------------------------------
# %m | Month as a zero-padded decimal number.| 01, 02, …, 12
# ------------------------------------------------------------------------
# %y | Year without century as a zero-padded | 00, 01, …, 99
# | decimal number. |
# ------------------------------------------------------------------------
# %Y | Year with century as a decimal number.| 0001, 0002, …, 9999
# ------------------------------------------------------------------------
# %H | Hour (24-hour clock) as a zero-padded | 00, 01, …, 23
# | decimal number. |
# ------------------------------------------------------------------------
# %I | Hour (12-hour clock) as a zero-padded | 01, 02, …, 12
# | decimal number. |
# ------------------------------------------------------------------------
# %p | Locale’s equivalent of either AM / PM | AM, PM (en_US);
# ------------------------------------------------------------------------
# %M | Minute as a zero-padded decimal number| 00, 01, …, 59
# ------------------------------------------------------------------------
# %S |Second as a zero-padded decimal number.| 00, 01, …, 59
# ------------------------------------------------------------------------
# %f | Microsecond as a decimal number, | 000000, 000001, …, 999999
# | zero-padded on the left. |
# ------------------------------------------------------------------------
# %z | UTC offset in the form | (empty), +0000, -0400, +1030,
# | ±HHMM[SS[.ffffff]] | +063415, -030712.345216
# | (empty string if the object is naive) |
# ------------------------------------------------------------------------
# %Z | Time zone name | (empty), UTC, GMT
# | (empty string if the object is naive) |
# ------------------------------------------------------------------------
# %j | Day of the year as a zero-padded | 001, 002, …, 366
# | decimal number. |
# ------------------------------------------------------------------------
# %U | Week number of the year | 00, 01, …, 53
# | (Sunday as the first day of the week) |
# | as a zero padded decimal number. |
# | All days in a new year preceding the |
# | first Sunday are considered to be |
# | in week 0. |
# ------------------------------------------------------------------------
# %W | Week number of the year | 00, 01, …, 53
# | (Monday as the first day of the week) |
# | as a decimal number. All days in a |
# | new year preceding the first Monday |
# | are considered to be in week 0. |
# ------------------------------------------------------------------------
# %c | Locale’s appropriate date and | Tue Aug 16 21:30:00 1988 (en_US)
# | time representation. | Di 16 Aug 21:30:00 1988 (de_DE)
# ------------------------------------------------------------------------
# %x | Locale’s appropriate date | 08/16/88 (None)
# | representation. | 08/16/1988 (en_US)
# | | 16.08.1988 (de_DE)
# ------------------------------------------------------------------------
# %X | Locale’s appropriate time | 21:30:00 (en_US);
# | representation. | 21:30:00 (de_DE)
# ------------------------------------------------------------------------
# %% | A literal '%' character. | %
Example 2: strtotime format
$date = '25/05/2010';
$date = str_replace('/', '-', $date);
echo date('Y-m-d', strtotime($date));