Debian 7 come with php 5.4.x. and it is now not secure now plus it is very good idea to get updated. right now php 5.6 or 7 can be upgraded. But php 7 is in beta now and lots of other thing related in not clear to me right now. so i am going with php 5.6.
now how can we upgrade my server to php 5.4 to php 5.6 with out any problem. i found out that official packages is not yet added to php 5.6. so i was looking for third party solution. and i found one https://www.dotdeb.org/instructions/ it is very good as it explain how to do it.
now lets start by editing the source.list file in debian.
sudo nano /etc/apt/sources.list
and add this line to your file.
for debian jessie
deb https://packages.dotdeb.org jessie all
deb-src https://packages.dotdeb.org jessie all
for debian wheezy
deb https://packages.dotdeb.org wheezy all
deb-src https://packages.dotdeb.org wheezy all
for debian squeeze
deb https://packages.dotdeb.org squeeze all
deb-src https://packages.dotdeb.org squeeze all
now to install php 5.6 from there repo add this line on the same file too
for debian wheezy (without Zend thread safety)
deb https://packages.dotdeb.org wheezy-php56 all
deb-src https://packages.dotdeb.org wheezy-php56 all
for debian "Wheezy" (with Zend thread safety)
deb https://packages.dotdeb.org wheezy-php56-zts all
deb-src https://packages.dotdeb.org wheezy-php56-zts all
now save the file and do the next command below
sudo apt-key add dotdeb.gpg
Now do this command in terminal
sudo apt-get updare
sudo apt-get install php5
after that check your php version by typing "php -v" in terminal of you can use phpinfo(); in php file.