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As you learned in the previous exercise, a basic

RewriteRule

takes two arguments. In this example it also

received a special flag —

[L]

— as a third argument. The meaning of these arguments is discussed next.

The first argument of

RewriteRule

is a regular expression that describes the

matching

URLs you

want to rewrite. The second argument specifies the destination (

rewritten

) URL. So, in geek-speak, the

RewriteRule

line basically says: rewrite any URL that

matches

the

^Products/P([0-9]*)\.html$

pattern to

/product.php?product_id=$1

. In English, the same line can be roughly read as: “dele-

gate any request to a URL that looks like

Products/P

n

.html

to

/product.php?product_id=

n

”.

Let’s analyze in detail the regular expression that describes the matching URLs that need to be rewritten.

That regular expression is:

^Products/P([0-9]*)\.html$

Most characters, including alphanumeric characters, are read literally and simply match themselves.

Remember the first

RewriteRule

you’ve written in this chapter to match

my-super-product.html

,

which was mostly created of such “normal” characters.

What makes regular expressions so powerful (and sometimes complicated), are the special characters (or

metacharacters

), such as

^

,

.

, or

*

, which have special meanings. Table 3-3 describes the metacharacters

you’ll meet.

Remember that this theory applies to regular expressions in general. URL rewriting is just one of the

many areas where regular expressions are used.

Table 3-3

Table continued on following page

Metacharacter Description

^

Matches the beginning of the line. In our case, it will always match the beginning of

the URL. The domain name isn’t considered part of the URL, as far

RewriteRule

is

concerned. It is useful to think of

^

as “anchoring” the characters that follow to the

beginning of the string, that is, asserting that they be the first part.

.

Matches any single character.

*

Specifies that the preceding character or expression can be repeated zero or more

times — not at all to infinite.

+

Specifies that the preceding character or expression can be repeated one or more

times. In other words, the preceding character or expression must match at least

once.

?

Specifies that the preceding character or expression can be repeated zero or one

time. In other words, the preceding character or expression is optional.

{m,n}

Specifies that the preceding character or expression can be repeated between

m

and

n

times;

m

and

n

are integers, and

m

needs to be lower than

n

.

57

Chapter 3: Provocative SE-Friendly URLs

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