How does PHP work?

For 2023 (and 2024 ...) - we are now fully retired from IT training.
We have made many, many friends over 25 years of teaching about Python, Tcl, Perl, PHP, Lua, Java, C and C++ - and MySQL, Linux and Solaris/SunOS too. Our training notes are now very much out of date, but due to upward compatability most of our examples remain operational and even relevant ad you are welcome to make us if them "as seen" and at your own risk.

Lisa and I (Graham) now live in what was our training centre in Melksham - happy to meet with former delegates here - but do check ahead before coming round. We are far from inactive - rather, enjoying the times that we are retired but still healthy enough in mind and body to be active!

I am also active in many other area and still look after a lot of web sites - you can find an index ((here))

How does PHP work?

From Learning to Program in PHP and PHP Programming - presented this week, and repeating at regular intervals - see schedule.

Let's say that I want a web page - with a single URL (Uniform Resource Locator / name) - to show up differently in my browser depending on how I run it ...
• I write the text that's to appear on the page into a text file
• I add HTML (Hypertext Markup Language) tags - extra bits of information enclosed in < through to > characters - which indicate what's to be headlines, what's to be italics, etc.
• I add further tags which include program elements that are to run before the data is displayed, enclosed in <?php through to ?> character sets and within those tags I write in the PHP programming language.
Then ..
• I store the text file on my web server computer, in an appropriate place for the web server software (most commonly the Apache httpd server) to locate it when the appopriate URL is used by a client (that's your browser, or an automated program such as the Google indexing robot) to find it.
• I configure my server to run the program elements enclosed in the <?php through to ?> character sets (this is often a once-only job telling the server that anything ending in .php is to be handled that way.

Then when someone calls up my file via its URL ...
• The SERVER relpaces the <?php through to ?> sets with the result of running that code and passes it on (across the internet) to
• the CLIENT which follows the instructions in the remaining < through to > character blocks as regards formatting and
• displays the untagged (unblocked) text.

Each of these stages can be seen / viewed if you wish to do so. In this screen capture, the original file as stored on the web server is seen at the bottom of the diagram. Above it (and to the right) is the text stream that's outputbythe web server and passed to the browser - we can see this by using the "view source" button on our browser (most browsers and do this). And in the top left of the screen capture is what the user sees through his / her browser.

That's a straightforeard example of the mechanism of PHP ... all I've done is to insert the day of the week into this particular page. But just think how much more I can do as I read forms from the user to control what gets sent out, access databases on the server, and even call up other web sites from within my PHP ...
(written 2012-11-07, updated 2012-11-10)

Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles

W603 - Web and Intranet - Server Side Technologies
  [642] How similar are two words - (2006-03-11)
  [653] Easy feed! - (2006-03-21)
  [732] Where is a web site visitor browsing from - (2006-05-24)
  [1020] Parallel processing in PHP - (2007-01-03)
  [1031] robots.txt - a clue to hidden pages? - (2007-01-13)
  [1355] .php or .html extension? Morally Static Pages - (2007-09-17)
  [1365] Korn Shell scripts on the web - (2007-09-25)
  [1554] Online hotel reservations - Melksham, Wiltshire (near Bath) - (2008-02-24)
  [1615] PHP training courses every month - (2008-04-18)
  [1749] Using server side and client side programming together - (2008-08-11)
  [2055] Effect on server when memory runs out and swapping starts - (2009-02-26)
  [2282] Checking robots.txt from Python - (2009-07-12)
  [3705] Django Training Courses - UK - (2012-04-23)
  [4277] Sending a message to the server and changing text on a page when a button is pressed - (2014-05-23)

H102 - A First PHP Web Page
  [624] It's REALLY easy to add a little PHP - (2006-02-26)
  [1448] Question on division (Java) - Also Perl, PHP, Python ... - (2007-11-28)
  [2432] Using print_r in PHP to explore mysql database requests - (2009-10-01)
  [4074] A comment on comments in PHP - (2013-04-28)

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While, for, foreach or something else to loop.

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PHP variables - dynamically typed. What does that mean?

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This is a page archived from The Horse's Mouth at http://www.wellho.net/horse/ - the diary and writings of Graham Ellis. Every attempt was made to provide current information at the time the page was written, but things do move forward in our business - new software releases, price changes, new techniques. Please check back via our main site for current courses, prices, versions, etc - any mention of a price in "The Horse's Mouth" cannot be taken as an offer to supply at that price.

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