date +%F

Fmt Description
DAY ===========================================================
d    Day of the month, 2 digits with leading zeros
D    A textual representation of a day, three letters
j    Day of the month without leading zeros
l    A full textual representation of the day of the week
S    English ordinal suffix for the day of the month, 2 characters
w    Numeric representation of the day of the week
z    The day of the year (starting from 0)

WEEK ==========================================================
W    ISO-8601 week number of year, weeks starting on Monday (added in 
PHP 4.1.0)

MONTH =========================================================
F    A full textual representation of a month, such as January or March
m    Numeric representation of a month, with leading zeros
M    A short textual representation of a month, three letters
n    Numeric representation of a month, without leading zeros
t    Number of days in the given month

YEAR ==========================================================
L    Whether it's a leap year
Y    A full numeric representation of a year, 4 digits
y    A two digit representation of a year

TIME ==========================================================
a    Lowercase Ante meridiem and Post meridiem
A    Uppercase Ante meridiem and Post meridiem
B    Swatch Internet time
g    12-hour format of an hour without leading zeros
G    24-hour format of an hour without leading zeros
h    12-hour format of an hour with leading zeros
H    24-hour format of an hour with leading zeros
i    Minutes with leading zeros
s    Seconds, with leading zeros

TIMEZONE ======================================================
I    Whether or not the date is in daylights savings time
O    Difference to Greenwich time (GMT) in hours
T    Timezone setting of this machine
Z    Timezone offset in seconds. Zones west of UTC are negative, east 
are positive.

FULL DATETIME =================================================
c    ISO 8601 date (added in PHP 5)
r    RFC 2822 formatted date
U    Seconds since the Unix Epoch (January 1 1970 00:00:00 GMT)