Upgrading code from PHP4 to 5.4+

Hi there, I have a customer who have a few customer developed sections on their website that was many years ago now and worked fine running on PHP4.  Their hosting provider now let them know that PHP4 will be unsupported soon so they'd have to upgrade to at least 5.4.  We did a quick test and it does break most if on PHP 5.4.

I did a couple PHP projects about 10 years ago now so I can help myself but I thought I'd here for some hints of the most important things to change so it will work for 5.4 or later. I found this - http://php.net/manual/en/migration5.incompatible.php - but their site doesn't do anything fancy, advice for obvious things to check would be very handy thanks!
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ebooyensAsked:
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Slick812Connect With a Mentor Commented:
I looked at the PHP manual page "Backward Incompatible Changes" that you gave, it gives very many of things to consider for a Change to the newer PHP version. Not sure what else you may be looking for as advice to change, seems like it covers it.
Unfortunately for me, I had the task of updating an old php coded site. I found that I would spend less time, if I used (copy and paste, include) code I have done for other projects that gave same or similar PHP results for the database and Page display required, , ,  NOT referring to the old code except to get file names, sever locations, etc, instead of going line by line in the old code and trying to FIX it. That old code was so outdated and slack, that even if corrected to working, it was not a good thing.
Also updating the site to newer HTML standards for size (1600x900, mobile) and "Look" (dynamic-HTML, Div, span, overlap, javascript) was not in the old site code. So might you start from scratch, and use more modern methods of php and DHTML, and have less time used, if you have some of your own coding that does what the pages need to do? ? ?
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Dave BaldwinConnect With a Mentor Fixer of ProblemsCommented:
There are some serious changes at each step in PHP 5.1, 5.2, 5.3, and 5.4, not just from PHP 4 to 5.  Each step gets less and less tolerant of programming errors.  In particular, undeclared variables and array indexes are not ignored anymore.

A site I am working on right now failed when moving from PHP 4 to PHP 5.2 because it was using the old PHP GET ($HTTP_GET_VARS) and POST ($HTTP_POST_VARS) variables and the developer had substituted 'preg_match' for 'ereg' without modifying the regex strings.
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ebooyensAuthor Commented:
Thanks both, very helpful, I've started looking at the code now so trying to figure out how bad it's going to be!
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