Regular expressions are widely used in programming and intensions of regular expressions are to manipulate complex strings in terms of replacing parts or all of them, finding particular pattern, etc... .

PHP uses the POSIX extended regular expressions as defined by POSIX 1003.2 or a regular expression library is compatible with PERL called PCRE which consists a set of functions having the same syntax as PERL 5

You can learn more about REGEX (regular expressions) on these two links:


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