help with preg_match for detecting < - and > characters

[mjs87]

Hi I'm trying to use preg_match to stop the <, - and > characters from being input in a text field. I have read that the < and > characters have to be escaped e.g. /< and /> however \< and \> are anchors in regex? If anyone can help i'd really appreciate it, thanks in advance!

[joe92]

Why do you need these characters to be prevented from being put into your textfield? If it is because you don't want them ending up in your database, there is a built in function called htmlspecialchars and another called htmlentities which will make those characters and more safe for you.

 

If its for another reason, please provide the code you have already tried, i.e. the full pattern, so we can help you

[mjs87]

if(preg_match('[\>]', $this->Results->Text))
return “Error – Results contains invalid characters”;

 

Unfortunately it’s for another reason, so my only option is to use preg_match. I have tried the above which seems to detect the > character. However I don’t understand why /> needs to be enclosed in the square brackets because the square brackets mean a range? Also I’m not too sure how to go on and detect the – and < characters? Thanks

 

[joe92]

The [] means character class. It can be a range of characters, i.e. [0-9] which will match a digit from 0-9, or it can be individual sets of characters, [abc] which will match a or b or c. As the dash means range, you have to escape it with \-. However, the < sign and the > sign do not need to be escaped if placed within a charater class. Heres some more info on that. That guide is gold, do read it if you get some time, but especially read that section to understand which metacharaters need to be escaped within character classes.

 

if(preg_match('/[<>\-]/s', $this->Results->Text))

 

I don't know in what enviroment you are using it in and I haven't tested it so let me know if it doesn't work.

 

Hope this helps,

Joe

[mjs87]

That works thank you. Just for my understanding what does the / before the [ do and the /s after the ]? I’ve read the link but can’t work out what these two things are doing? Thank for your help

[joe92]

The forward slashes are delimiters. The are used to contain the bounds of the pattern. There are several types of delimiters including ~ and %. They each have different pro's and con's and I don't claim to understand the differences between them all.

 

The s after the closing delimiter is a pattern modifier. Heres a list of all the modifiers available and their meanings.

 

p.s. Mark the topic as solved

[mjs87]

Great thanks for your help... I'm starting to get a better understanding of regex