PHP and MySQL Web Development 4th Ed-tqw-_darksiderg

Finding Substrings with Regular Expressions
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The subexpression ^[a-zA-Z0-9_\-.]+ means “start the string with at least one letter,
number, underscore, hyphen, or dot, or some combination of those.” Note that when a
dot is used at the beginning or end of a character class, it loses its special wildcard meaning
and becomes just a literal dot.
The @ symbol matches a literal @.
The subexpression [a-zA-Z0-9\-]+ matches the first part of the hostname including
alphanumeric characters and hyphens. Note that you slash out the hyphen because it’s a
special character inside square brackets.
The \. combination matches a literal dot (.).We are using a dot outside character
classes, so we need to escape it to match only a literal dot.
The subexpression [a-zA-Z0-9\-\.]+$ matches the rest of a domain name, including
letters, numbers, hyphens, and more dots if required, up until the end of the string.
A bit of analysis shows that you can produce invalid email addresses that will still
match this regular expression. It is almost impossible to catch them all, but this will
improve the situation a little.You can refine this expression in many ways.You can, for
example, list valid top-level domains (TLDs). Be careful when making things more
restrictive, though, because a validation function that rejects 1% of valid data is far more
annoying than one that allows through 10% of invalid data.
Now that you have read about regular expressions, you’re ready to look at the PHP
functions that use them.
Finding Substrings with Regular Expressions
Finding substrings is the main application of the regular expressions you just developed.
The two functions available in PHP for matching POSIX-style regular expressions are
ereg() and eregi().The ereg() function has the following prototype:
int ereg(string pattern, string search, array [matches]);
This function searches the search string, looking for matches to the regular expression
in pattern. If matches are found for subexpressions of pattern, they will be stored in
the array matches, one subexpression per array element.
The eregi() function is identical except that it is not case sensitive.
You can adapt the Smart Form example to use regular expressions as follows:
if (!eregi(‘^[a-zA-Z0-9_\-\.]+@[a-zA-Z0-9\-]+\.[a-zA-Z0-9\-\.]+$’, $email)) {
echo "That is not a valid email address.".
Please return to the previous page and try again.";
exit;
}
$toaddress = “feedback@example.com”; // the default value
if (eregi(“shop|customer service|retail”, $feedback))