![]() ![]() ![]() It is important to note, that it is actually possible to account for all special cases. If suddenly something changes, the HTML has an extra unexpected space or new line somewhere, your code might stop working. If you are crawling web pages, then you also need to account for pages with invalid character sets, since some pages do not match the character set that the server says is used. There is just to many different, valid, ways to write HTML - and then you probably also need to support some degree of invalid HTML. The problem with using RegExes for HTML is that HTML is irregular. What you can not expect, is to create a "parser" that will work on all thinkable HTML with RegExes. You will often be told not to use regular expressions to work on HTML code, and instead use DOM tools - but let me be absolutely clear - there is nothing wrong with using regular expressions to alter HTML code! ![]() The question mark in the pattern makes the expression non-greedy, meaning it will only match up until the closing Using regular expressions for HTML However, when working with HTML, this might prevent nested elements - more on this in the section on nested elements!įinally, preg_replace also works with arrays in the same way that str_replace does. For instance, instead of listing all the characters that you allow, it is often much easier to simply list those that you do not allow using the caret inside square brackets. It is often a good idea to use reverse-logic in your expressions. So, whenever you work with expressions and nested parentheses, keep this in mind. This can be shown by a visual representation: For nested parentheses, the matches are stored in the order that they are matched, from the inside-out – like the layers of an onion. Back references can be accessed by the numeric variables: $1, $2 ,$3. The parentheses are used to remember the match as a "back reference", which allows us to insert it into the replacement string. The Square brackets ( ) are used to match a series of unordered characters in this case we used the caret/circumflex/hat sign to state which characters should not be matched. In this case I used u the u modifier will cause the pattern and subject strings to be treated as UTF-8. The part at the end, u are the modifiers. We already explained the plus sign earlier. The part located inside the parentheses matches the content, basically it matches all characters except for the less than ( <) sign. The regex used to match the pattern in the $str variable above is relatively simple: $str = ' My first Website My first Website. It is possible to use bare strings, variables and arrays. The str_replace function can be used by feeding it with a target string, a replacement string, and a source string. When multiple calls to str_replace is needed, that is probably a good time to use regular expressions instead, since that is when preg_replace may actually be the faster option. Now, this does not mean that I recommend one over the other-if it is possible to use the string version, then I think you should aim to do so, since it is such an easy thing to do. Last time I tested this, I was able to do more than 1 million replacements in about a second on an i3 laptop it will only matter for high-performance applications. While the string functions are said to be faster than using regular expressions in preg_* functions, this rarely seem to matter in practice. The native str_replace function of PHP is used to replace all the occurrences of a given string with a replacement string but using a regular expression will allow for more complex pattern-based replacements, which is useful for working with HTML, CSS and JavaScript content. To replace a substring within a string we can either use the string replacement functions, or we can create a regular expression for more complex replacements.Ī simple way to replace a string is by using the str_replace (for a case sensitive replacement) or stri_replace (for a case insensitive replacement) but we can also use preg_replace to perform regular expression replacements. ![]()
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