PHP
By Web Monkey
Page 3 — Not-So-Simple Validation
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Let's talk a bit about using regular expressions with the
ereg() and eregi() functions. As I said earlier, these can
be either quite complex or very simple, depending on what
you need.
Using regular expressions, you can examine a string and intelligently
search for patterns and variations to see whether they match
the criteria you set. The most common of these involves checking
whether an email address is valid (although, of course, there's
no fail-safe way of doing this).
Rather than delve into the mysteries of regular expressions,
I'll provide some examples. You can use the same form we created
on the previous page - just paste in the lines below to see
how they work.
First, let's make sure that text only has been entered into
a form element. This regular expression tests true if the
user has entered one or more lowercase characters, from a
to z. No numbers are allowed:
if (!ereg("[a-Z]",
$first) || !ereg("[a-Z]", $last)) {
Now, let's extend this expression to check whether the string
is four to six characters in length. Using [[:alpha:]] is
an easy way to check for valid alphabetic characters. The
numbers in the braces check for the number of occurrences.
And note that the ^ and $ indicate the beginning and end of
the string.
if
(!ereg("^[[:alpha:]]{4,6}$", $first) || !ereg("^[[:alpha:]]{4,6}$",
$last)) {
Finally, let's build a regular expression that will check
an email address' validity. There's been plenty of discussion
about the effectiveness of checking for email addresses in
this way. Nothing's completely foolproof, but what I have
below works pretty well.
I took this gem from the PHP mailing list. It's a great resource
- use it. And yes, this is as scary as it looks.
if (!ereg('^[-!#$%&\'*+\\./0-9=?A-Z^_`a-z{|}~]+'.
'@'.
'[-!#$%&\'*+\\/0-9=?A-Z^_`a-z{|}~]+\.'.
'[-!#$%&\'*+\\./0-9=?A-Z^_`a-z{|}~]+$',
$last)) {
Don't spend too much time looking at this. Just move on to
the next page.
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