Page 577 - Beginning PHP 5.3

18

String Matching with

Regular Expressions

In Chapter 5 you explored many of PHP ’ s powerful string manipulation functions, such as
strstr() for finding text within a string and str_replace() for searching and replacing text
within a string.

In this chapter you learn about PHP ’ s even more powerful regular expression functions. These
give you a lot more flexibility than the regular string - matching functions because they let you
compare a string against a pattern of characters rather than against a fixed string. For example,
you can search a string for a pattern of characters comprising exactly three digits, followed by
either a comma or a dot, followed by from one to four letters.

Within a regular expression you use special symbols such as ? and ^ to specify a pattern. Because
patterns can get quite complex, it can be hard to decipher regular expressions when you first start
out. However, with a bit of practice, as well as some of the hints in this chapter, you ’ ll find that you
can read regular expressions much more quickly and easily.

Although regular expressions aren ’ t essential to PHP programming — you can usually do a similar
job with the string matching functions and a loop or two — they ’ re your best bet when you need to
match patterns. For one thing, a single regular expression is usually much more compact and
intuitive than a whole series of string matches and loops. The expression will often run much
quicker, too.

By the time you ’ ve read this chapter you ’ ll know about:

❑ Matching strings against regular expressions: You explore PHP ’ s preg_match() and

preg_match_all() functions that let you apply regular expressions to strings to
find matches
❑ The ins and outs of regular expression syntax: You learn all about the special characters

used in regular expressions, as well as how to match character types, several characters at
once, alternative groups of characters, and much more

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