php using date and time for various purposes

We always need to deal with date and time in our programming specially when we are using php .
time() and date() these two functions are very important regarding our concern .

see following line of php code :-
$a = time();
time() function returns total number of seconds passed till date from 1st jan 1970 .
date() function is used to get date formatted according to our wish .
function date() can have two parametes:-
1) format of time stamp that we want to show
2) optional:- timestamp which we need to use to get date

first parameter is string that shows that exact output format  . some characters are usefull like
Y -- to show current year
m -- to show current month number
d -- to show today's dat
H -- current hour   24 hour format
i -- to show current minute
s -- to get current seconds
t -- shows number of days in current month  or last date of current month


following are some uses date() function :-

echo  date(""); // this will print nothing
echo date("Y-m-d H:i:s"); // this will show complete time stamp i.e.  2013-10-16 12:00:00 as your system time

echo date("Y-9-d 12:00:s"); // this will show  2013-9-16 12:00:45

these were examples of formatting of time stamp that we want to show ;

second parameter is time stamp itself .
for example :-

 echo date("Y-m-d H:i:s" , time());  // this will show  current time
  echo date("Y-m-d H:i:s" , time() + 500);  // this will show  time after 500 seconds

  echo date("Y-m-d H:i:s" , time() + 86400 );  // this will show tomorrow's time because 86400 is number of seconds in one day .

if we want to see time 5 days ahead  then we need to do is
  echo date("Y-m-d H:i:s" , time()  + 5*86400);

similarly if we want to see time 5 days back then we need to do is
  echo date("Y-m-d H:i:s" , time()  - 5*86400);


if we need to find how many days are in this month or any month then we use "t" in format string (first parameter) .
like

$number_of days_this month = date("t"); // it will give only last date of the month

Thanks and please ask in comment if you need any clearification .

PHP file to return image or return 1x1 pixel image

Using php file we can return image .  there are many benefits of this thing . we can keep count that how many times our image is fetched or from which us/ip that image is fetched.also we can change image from php code without changing in the real html file .

see following code

<img src="http://localhost/test.php"/>

if we want that test.php should return any image
following is the code snippet to return that image

test.php :-

$file = file_get_contents("full path to ur image fle");
$contenttype = "gif" ; // it is type or extension of image like jpeg for jpeg images and gif for .gif images
header("Content-type: image/$contenttype");
echo $file;

we need to  take care of some thing in this .
we should not print or echo any other variable or string from the same php file .then it will be showing some error and image will not be returned .

IF we want to return 1x1 image pixel then following is the code snippet .

header('Content-Type: image/gif');
header('Content-Length: 43');
echo base64_decode('R0lGODlhAQABAIAAAP///wAAACH5BAAAAAAALAAAAAABAAEAAAICRAEAOw==');


this code will provide us 1x1 image 

python check if variable is empty

This is very easy to know in python that if any variable is empty or not

try to use :

if not ur_var:
     print "variable is empty 

get attention towards   not   keyword . This does all things .

This is equivalent to empty($ur_var)  in php

not keyword in python also checks for lists (array) , objects , strings , integrers , floats etc ..

example :

a= 0  or a = "" or a ={} or a= []
if not a :
    print "empty"

in all cases it will print empty .

linux set ulimit

for setting ulimit u need to run following command

ulimit -n  10000  for setting limit to 10000

for soft files  
ulimit -Sn  10000

and for hard files
ulimit -Hn 10000


do it individually for all users

and this setting will be vanished after system restart