Patterns

[pinchepunk]

I am working on patterns right now and have a couple of simple questions. I got the following piece of code from the book I am using to check on a URL and would appreciate a better explanation of the different pieces of it. Ignore the underlining.

$pattern = "([url]http://[/url])?([^{[:space:]]+)([[:alnum:].,-_?/&=])";}

I understand that we are telling it that data we will be gathering can start with the [url]http://[/url] but that this is optional, that it can not be followed by a space, and that it may be followed by any number, letter, slash, quetion mark, ampersand, and equals sign. My questions are as follows:

First of all, what exactly do the question (+) marks mean. There was no formal explanation in my book and it would help me to remember to use them if I knew what they meant.

Second, wouldn't it be better to have something like the following to make sure someone uses a valid URL:

$pattern = "([url]http://[/url])?([^{[:space:]]+)([[:alnum:].,-_?/&=]).([:alnum:]+)";}

I'm sure there much better ways to check for a URL and if any one can give me their version along with a brief explanation I would greatly appreciate it.

Thanks!

[dalecosp]

Well, 'round here these are called 'regular expressions.' It looks like you're studying the POSIX type RE's.

Also, a question mark looks like this (?) and that other thing is a 'plus' sign.... 🙂

The + sign is one of three regular expression 'metacharacters'

a* = 'zero or more a's'
a+ = 'one or more a's'
a? = 'one or less a's' (ie 'could be an a, or not')

HTH,