more regular expression confusion. help plz!

Paul_help_

Hi folks.

I am having trouble understanding a couple of little snippets from the code beneath:

// Displays “71%, 83%”
echo preg_replace( “/\d+\%(,| )*/”, “”, “14%, 59%, 71%, 83%”, 2 );

The thing i can't understand is why this is needed:

(,| )*

I don't understand what needs to be multiplied,, becoz it looks like its multiplying nothing.

And i don't understand what (,| ) does. To me it looks like its saying:

a comma 'or' a space

but it can't mean that, surely??

bradgrafelman

Paul help!;11033879 wrote:
I don't understand what needs to be multiplied,, becoz it looks like its multiplying nothing.

The asterisk in a regular expression pattern only loosely relates to the mathematical operator; it means "the previous item appears zero or more times" (where the "item" in this pattern is the parenthetical group).

Paul help!;11033879 wrote:
And i don't understand what (,| ) does. To me it looks like its saying:

a comma 'or' a space

but it can't mean that, surely??

Why can't it mean that? (Trick question, since that's exactly what it means.)

I would highly recommend you read through a website like Regular-Expressions.info and learn the basics of regular expression syntax.

Paul_help_

I just realized what the star (*) sign means. i completely forgot.

I have learned a lot of the basics. i just keep forgetting some of the fiddly little bits.

Ok. Just to make sure.. The star means the whole regular expression can appear zero or more times?? (can you confirm this for me, just so i know im correct?)

..... and the i need to ask about this:

QUOTE [/QUOTE]

... is this considered a sub pattern???

... and why not (, & ) instead?? since both the comma and white space appear in the string????

Weedpacket

Paul help! wrote:
The star means the whole regular expression can appear zero or more times?

No, just the subpattern immediately to the left.

Paul help! wrote:
... is this considered a sub pattern???

Yes.

... and why not (, & ) instead??

Because [font=monospace]|[/font] was the symbol chosen to represent the alternation operator, not [font=monospace]&[/font].