Re: Using undefined back-references?

It is one of reasons why non-capturing groups (?:...) are invented. In those cases when you do not need capturing, or get something optional in your string, just use them.

In a line where you wrote:

(\s+[^>]*)?\s+       # Optional assorted crud
[download]

write another way:

(?:\s+[^>]*)?\s+       # Optional assorted crud
[download]

Courage, the Cowardly Dog

addition: I suggest you to use a trick that fruiture later advices to you. Personally, I use that trick quite often.

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Re: Re: Using undefined back-references? by tommyw (Hermit) on Aug 19, 2002 at 16:22 UTC
Won't do it, I'm afraid, 'cos I actually need to keep that crud, if it exists. Especially if somebody throws me the attributes in a different order: <e st="obs" num="1" st="ali"> needs to group in the same way. By using ?: the entire intermediate string disappears, and I end up with <e st="obs,ali"> Which wasn't precisely what I was after. Although it does shut the warning up :-) -- Tommy Too stupid to live. Too stubborn to die.	[reply]
Re: Re: Re: Using undefined back-references? by fruiture (Curate) on Aug 19, 2002 at 16:31 UTC
How about `((?:\s+[^>])?)\s+ # Optional assorted crud` [download] ? The capturing () is not marked with ? (or ) so it won't be undef, but the non-capturing (?:) is marked with ?, so it can fail to match: in that case the () saves an empty string, not undef. -- http://fruiture.de	[reply] [d/l]