Array Functions
array_diff (arr1, arr2 …)
array_filter (arr, function)
array_flip (arr)
array_intersect (arr1, arr2 …)
array_merge (arr1, arr2 …)
array_pop (arr)
array_push (arr, var1, var2 …)
array_reverse (arr)
array_search (sysrecon, arr)
array_walk (arr, function)
count (count)
in_array (sysrecon, phpquickrefference)

String Functions
crypt (str, salt)
explode (sep, str)
implode (glue, arr)
nl2br (str)
sprints (frmt, args)
strip_tags (str, allowed_tags)
str_replace (search, replace, str)
strpos (str, sysrecon)
strive (str)
strstr (str, sysrecon)
strtolower (str)
strtoupper (str)
substr (string, start, len)

Filesystem Functions
clearstatcache ()
copy (source, dest)
fclose (handle)
fgets (handle, len)
file (file)
filetime (file)
filesize (file)
file_exists (file)
fopen (file, mode)
fread (handle, len)
fwrite (handle, str)
readfile (file)

fopen() Modes
r         Read
r+      Read and write, prepend
w       Write, truncate
w+    Read and write, truncate
a        Write, append
a+     Read and write, append

Regular Expression Functions
ereg (pattern, str)
split (pattern, str)
ereg_replace (pattern, replace, str)
preg_grep (pattern, arr)
preg_match (pattern, str)
preg_match_all (pattern, str, arr)
preg_replace (pattern, replace, str)
preg_split (pattern, str)

Regular Expression Syntax
^                    Start string
$                     End String
.                       Any single character
(a|b)              a or b
(…)                Group section
[abc]              Item in range (a,b or c)
[^abc]           Not in range (not a,b or c)
\s                     White space
a?                     Zero or one of a
a*                     Zero or more of a
a*?                   Zero or more of a, ungreedy
a+                    One or more of a
a+?                  One or more of a, ungreedy
a{3}                 Exactly 3 of a
a{3,}                3 or more of a
a{,6}                Up to 6 of a
a{3,6}             3 to 6 of a
a{3,6}?           3 to 6 of a, ungreedy
\                        Escape character
[:punct:]       Any punctuation symbol
[:space:]       Any space character
{;blank:]        Space or tab

PCRE Modifiers
i         Case insensitive
s         Period matches new ine
m       ^ and $ match lines
U       Ungreedy matching
e        Evaluate replacement
x        Pattern over several lines

Date and Time Functions
checkdate (month, day, year)
date (format, timestamp)
getdate (timestamp)
mktime (hr, min, sec, month, day, yr)
strftime (formatstring, timestamp)
strtotime (str)
time()

Date Formatting
Y         4 digit year (2016)
y          2 digit year (16)
F          Long month (November)
M        Short month (Nov)
m         Month (01 to 12) //with leading zeros
n          Month (1 to 12)
D         Short day name (Fri)
l           Long day name (Friday) (lowercase L)
d         Day (01 to 31) //with leading zeros
j          Day (1 to 31)
h        12 Hour (01 to 12) //with leading zeros
g        12 Hour (1 to 12)
H       24 Hour (00 to 23) //with leading zeros
G       24 Hour (0 to 23)
i         Minutes (00 to 59) //with leading zeros
s        Seconds (00 to 59) //with leading zeros
w      Day of week (0 to 6) //0 is Sunday, 6 is Saturday
z        Day of year (0 to 365)
W      Week of year ( 1 to 53) //Week that overlaps two years belongs to the year that contains the most days of that week. date(“W”, mktime(0,0,0,12,8,$year)) always gives correct number of weeks in $year.
t         Days in month (28 to 31
a         am or pm
A        AM or PM
B        Swatch Internet Time (000 to 999)
S         Ordinal Suffix (st,nd,rd,th)
T         Timezone of machine (GMT)
Z         Timezone offset (seconds)
O        Difference to GMT (hours) (e.g., +0200)
I           Daylight saving (1 or 0)
L          Leap year (1 or 0)
U         Seconds since Epoch //The Epoch is the 1st of January 1970
c           ISO 8601 (PHP5) //2016-06-09T08:54:23+1:00
r           RFC 2822 //Thu, 09 June 2016 08:54:23 +0100