Question:What is regular expression?

 

Regular expressions provide the foundation for describing or matching data according to defined syntax rules. A regular expression is nothing more than a pattern of characters itself, matched against a certain parcel of text.

Question:What is the difference between ereg_replace() and eregi_replace()?

 

ereg_replace: The ereg_replace() function operates to finding and replacing a pattern with a replacement string.

eregi_replace : The eregi_replace() function operates exactly like ereg_replace(), except that the search for pattern in
string is not case sensitive. 

Question:What is the difference between ereg_replace() and eregi_replace()?

 

ereg_replace(): ereg_replace() function is case sensitive.
eregi_replace(): eregi_replace() function is not case sensitive. 

Question:What are the two regular expression syntaxes? 

There are two regular expression syntaxes in php. These are 1. POSIX syntax and 2. Perl syntax.