Advanced String Processing - How Regular Are Your Expressions - Page 2

by: PHP Builder Staff

May 19, 2009

So What Else Can Regular Expressions do?

The best way for me to describe that is to show you a few examples:

Let's say we have the string:

"Long live PHP Builder in 2009"

We can find and extract the 2009 using:

^.*(\d\d\d\d)$

If we use this in PHP with the preg_match function:

$found = preg_match("/^.*(\d\d\d\d)$/", "Long live PHP Builder in 2009",$matches);

$found will be true if the text provided had 4 digits at the end of the string, the / at either end of the pattern are how the regular expression engine knows the start and finish of the search (more on that in just a moment), if a match is found then the array matches will contain the following:

$matches[0] = "Long live PHP Builder in 2009" $matches[1] = "2009"

Here's how the reg-ex pattern reads:

^ = at the start of the line . = Read any character * = for as many as you can, until \d\d\d\d = you encounter 4 digits in a row $ = at the end of the string

() = keeps the part of the pattern you found in any rule between these separate, in this case the 4 digits.

or in English. Look for 4 consecutive digits that occur at the end of the string, and retrieve them.

Here's another one:

$text = "Peter Shaw" $reg-ex = "/(Peter)\s(Sh(aw|ore))/"

I'll not repeat the preg line this time.

The rule here says Return the first word before the space, and after the space match it if it's "Shaw" or a common misspelling "Shore", the pattern reads:

\s = look for the first space you encounter with Peter = on the left side of it and Sh = on the right side, followed by either (aw|ore) = 'aw' OR 'ore' In all cases keep the 2 found words.

The result in $matches will be

$matches[0] = "Peter Shaw" (or "Peter Shore") $matches[1] = "Peter" $matches[2] = "Shaw" (or "Shore") $matches[3] = "aw" (or "ore")

Pay attention above to the (aw|ore) bit. This has to be in () to group the 2 parts either side of the OR decision, so even if you don't intend to look for that part, it still uses up a slot in the results.

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